Symposium PP: Solid-State Chemistry of Inorganic Materials VII

f08_logo



Solid-State Chemistry of Inorganic Materials VII
December 1 - 5, 2008





Chairs  

Patrick M. Woodward
Dept. of Chemistry
Ohio State University
100 W. 18th Ave.
Columbus, OH 43210-1185
614-688-8274

   

John F. Mitchell
Materials Science Division #223
Argonne National Laboratory
9700 S. Cass Ave.
Argonne, IL 60439
630-252-5852

Stephanie L. Brock
Dept. of Chemistry
Wayne State University
5101 Cass Ave.
Detroit, MI 48202
313-577-3102

 

John S. Evans
Dept. of Chemistry University
Science Laboratories
Durham University
South Rd.
Durham, DH1 3LE United Kingdom
44-191-334-2093

Symposium Support
Los Alamos National Laboratory
National Science Foundation, Division of Materials Research

Proceedings to be published online
(see Proceedings Library at www.mrs.org/publications_library)
as volume 1148E
of the Materials Research Society
Symposium Proceedings Series.
 


* Invited paper
 

SESSION PP1: Novel Synthetic Methods
Chairs: Kyoung-Shin Choi and Patrick Woodward
Monday Morning, December 1, 2008
Back Bay C (Sheraton)


8:30 AM *PP1.1
New Aspects of Borate Chemistry under High-Pressure. Hubert Huppertz, Institut fuer Allgemeine, Anorganische und Theoretische Chemie, Leopold-Franzens-Universitaet Innsbruck, Innsbruck, Austria.

At the moment, over 1100 borate crystal structures are listed in the Inorganic Crystal Structure Database ICSD. High-pressure investigations are rare and have been mainly performed from a geological point of view. Starting in 1999, systematic high-pressure experiments up to maximum pressures of 16 GPa have been carried out in our group. In the context of these investigations into the high-pressure / high-temperature syntheses of new rare-earth and transition metal oxoborates, several new high-pressure polymorphs of known compositions, e.g. β-MB4O7 (M = Ca, Zn, Hg), χ-REBO3 (RE = Dy, Er), ν-DyBO3, γ-RE(BO2)3 (RE = La-Nd), δ-RE(BO2)3 (RE = La, Ce), and δ-BiB3O6 [1] were discovered. These investigations led to fundamental insights into the structural behaviour of oxoborates under high-pressure conditions. Especially the coordination of the boron and rare-earth atoms were of special interest in our investigations. Next to the synthesis of new modifications, new compositions were realized in our group. For example, all attempts to produce rare-earth metal(III) oxoborates with the ratio RE2O3:B2O3 = 2:3, 1:2, and 3:5 failed under normal-pressure conditions. In contrast, the corresponding high-pressure experiments led in most cases to phase pure rare-earth metal(III) oxoborates RE4B6O15 (RE = Dy, Ho)[2] and α-RE2B4O9 (RE = Sm-Ho), exhibiting the new and rare structural unit of edge-sharing tetrahedra. Our latest experiments yielded in a third compound, exhibiting edge-sharing tetrahedra. The special feature of the compound HP-NiB2O4 [3] is that in contrast to the first two compounds all tetrahedra are linked to each other via one common edge and two common corners. With the synthesis of β-HfB2O5 and β-SnB4O7 [4], we were able to synthesize the first crystalline compounds in the ternary systems Hf-B-O and Sn-B-O, respectively. Normally, these systems form glasses at ambient pressure conditions. No crystalline compounds were known in these systems. Now, the parameter pressure induces crystallization, which leads to defined crystalline compounds in both systems. The talk will introduce into several examples, which impressively underline the importance of the parameter pressure for the synthesis of new materials in solid state and materials chemistry. [1]J. S. Knyrim, P. Becker, D. Johrendt, H. Huppertz, Angew. Chem., Int. Ed. Engl. 2006, 45, 8239. [2]H. Huppertz, B. von der Eltz, J. Am. Chem. Soc. 2002, 124, 9376. [3]J. S. Knyrim, F. Roessner, S. Jakob, D. Johrendt, I. Kinski, R. Glaum, H. Huppertz, Angew. Chem., Int. Ed. Engl. 2007, 46, 9097. [4]J. S. Knyrim, F. M. Schappacher, R. Pöttgen, J. Schmedt auf der Günne, D. Johrendt, H. Huppertz, Chem. Mater. 2007, 19, 254.


9:00 AM PP1.2
Exploiting Reaction Pathways for the Targeted Synthesis of Diverse Oxide Materials. Mario Bieringer1, Shahid P Shafi1, Elizabeth Castillo-Martinez2 and Miguel A Alario Franco2; 1Department of Chemistry, University of Manitoba, Winnipeg, Manitoba, Canada; 2Departamento de Quimica Inorganica I, Universidad Complutense, Madrid, Spain.

Solid state materials can be prepared by a large number of different preparative methods. Variable temperature and pressure, solvent-free or solvent assisted methods such as sol-gel, hydrothermal and high temperature flux methods etc. provide a rich product variety. Solvent free solid state reactions are attractive due to their simplicity, the minimization of impurities and the elimination of costly product workups. In an attempt to manipulate properties of materials we explore the reaction pathways of ceramic preparation methods. Using variable pressure and variable temperature in conjunction with controlled reaction atmospheres a large variety of products can be manipulated at different stages during the synthesis. Cycling through pressure and temperature treatments adds additional degrees of freedom to structure modifications. Our in-situ methods have lead to the synthesis of a considerable number of novel intermediates at ambient pressure. Those intermediates and metastable products often lend themselves to high pressure conversions resulting in controlled cation and/or anion ordering processes. The highly strained products often exhibit unique physical properties. Recent experiments indicate that high pressure phases can in turn act as particularly intriguing intermediates for structural manipulations. Reaction pathways, preparative strategies, structural transitions and physical properties of some of these materials will be discussed.


9:15 AM PP1.3
Topochemical Modification of Layered Perovskites. Elisha Josepha, Jong Lak Choi, Xiao Zhang, Thathan Sivakumar and John B. Wiley; Department of Chemistry and Advanced Materials Research Institute, University of New Orleans, New Orleans, Louisiana.

Some members of the Dion-Jacobson (DJ) and Ruddlesden-Popper (RP) type layered perovskites can undergo structural modifications via topochemical manipulations. DJ perovskites, and select RP phases, are receptive to ion exchange and/or intercalation reactions. In some instances, one can use these methodologies to build new metal-halide and metal-oxide layers within receptive hosts, while in others, one can readily manipulate and control valence. Here we will present our recent results in the modification of layered perovskites. Efforts with both DJ and RP phases will be highlighted and new compounds, as well as effective single- and multi-step topochemical strategies, will be presented.


9:30 AM *PP1.4
Noncentrosymmetry in Mixed Metal Oxide-Fluorides, Can We Control it? Kenneth R. Poeppelmeier, Chemistry, Northwestern University, Evanston, Illinois.

The preparation of noncentrosymmetric materials, in particular how to differentiate polar, polar-chiral, and chiral structures, is one of the most challenging and interesting problems in modern solid state chemistry. Polar distortions in metal centered octahedra are postulated to be the origin of the nonlinear optical and ferroelectric response in metal oxides. Octahedrally coordinated transition metal cations such as Ti4+, Nb5+, and Mo6+ are unstable with respect to intraoctahedral distortions. Out-of-center distortions, which can be understood through the second order Jahn-Teller theorem, are commonly observed in both molecular species such as [NbOF5]2- and in LiNbO3 for example. The early transition metal oxide fluoride anions [VOF5]2-, [NbOF5]2-, [TaOF5]2- and [MoO2F4]2-, [WO2F4]2- from Groups 5 and 6, respectively, are well known inorganic species with large average nonlinear optical (NLO) bond susceptibilities. In the solid state these anions almost always crystallize with disorder which makes the detection of the distortions problematic and limits their interesting physical properties. To realize noncentrosymmetric structures, two goals must be met. First, the octahedra must crystallize without disorder. Second, the octahedra should order in a non-centrosymmetric arrangement with respect to each other, in other words, with no center of symmetry between the octahedra. Owing to disorder in the O/F metal bonds, however, these ions are seldom observed in noncentrosymmetric structures despite their acentric local structure. Various strategies to eliminate the O/F disorder and to synthesize noncentrosymmetric structures will be discussed.


10:30 AM *PP1.5
Liquid Metals as Solvents for Materials Discovery in Intermetallics. Mercouri G Kanatzidis, Department of Chemistry, Northwestern University, Evanston, Illinois; Division of Materials Science, Argonne National Laboratory, Argonne, Illinois.

The metallic flux is a powerful synthetic medium for the exploration of complex intermetallics. Just as the solubility of molecules in other molecules (i.e. solvents) enhances reactivity and reaction kinetics to produce new compounds, the solubility of metals in liquid metals (i.e. fluxes) results in analogous benefits. Well formed crystals of materials with complex and difficult to predict compositions often form in metallic fluxes. In this talk I will report on our recent results on the use of group 13 fluxes such as Al, Ga and In to discover several interesting intermetallics of ytterbium. The reactivity of rare earth elements including Yb and transition metals differs significantly in liquid Al, Ga and In. The structures and physical properties of the compounds YbFe4Al9Si6, RECoGa3Ge, Yb4MGe8 (M=Mn, Fe, Co, Ni), YbAuIn, and Yb3AuGe2In3 will be presented. In these phases, mixed-valency in the Yb atoms and magnetism in the transition metal atoms interact in complex ways to give rise to unusual phenomena ranging from unique valence instabilities to extended charge density waves.


11:00 AM PP1.6
Driving Electrons to Anti-Bonding States: On the Synthesis of New Niobium Cluster Chlorides by Electrochemical Lithium Intercalation. Flaviano Garcia-Alvarado1, Alois Kuhn1, Elena Gonzalo1 and H.-Jürgen Meyer2; 1Chemistry, Universidad San Pablo CEU, Boadilla del Monte, Madrid, Spain; 2Institut für Anorganische Chemie, Universität Tübingen, Tübingen, Germany.

LiNb6Cl15 is a crystalline solid whose structure (S.G. Ia -3 d) is built up from octahedral niobium clusters. The twelve edges of octahedra are occupied by chlorine. Three additional chlorines are located in apical position acting as Cl-bridges between Nb6 clusters. Lithium is occupying 1/3 of the 48f position [1]. The number of electrons available for bonding indicates that 16 electrons are located in M-M bonding state. However, the number of electrons can be modified by electrochemical lithium intercalation. Note that because the occupancy of lithium crystallographic position is only 33%, both insertion and extraction of lithium ions may be possible. In such a case it has to be accompanied by the injection or extraction of electrons respectively. We have already reported the synthesis of new clusters by this method but only to fill the bonding states up. This was the case of Ta6Cl15 , a 15 e- cluster that could be reduced to LiTa6Cl15, a new 16 e- cluster [2] in which all the bonding states are fully occupied. Attempts to prepare “Li1+xTa6Cl15” failed. The reaction of lithium with LiTa6Cl15 produces the irreversible reduction of Ta6Cl5. In this case the occupation of anti-bonding states, eg*, with the additional electrons may be at the origin of the observed decomposition. However, we report now a different behaviour found for the 16 e- niobium cluster LiNb6Cl15. It can be inserted with two more lithium ions. Hence, it seems that 2 electrons can be driven, likely, to eg*, by electrochemical reaction. Besides, the formation of Li3Nb6Cl15 is reversible showing that lithium electrochemical intercalation can be used to tune the number of electrons of the cluster. In this connection, we have found that lithium can be also reversibly extracted from LiNb6Cl15 to form Nb6Cl15, a 15 e- cluster similar to Ta6Cl15. Therefore, a complete and reversible path from the 15 to the 18 e- cluster seems to exist. The characteristics of the complete reaction: Nb6Cl15 + x Li ↔LixNb6Cl15 (0≤x≤3) have been analysed by using electrochemical techniques. Results indicate that, besides LixNb6Cl15 with x=0, 1 and 3, other intermediate phase, at x=1.5, seems to exist. The existence of all these phases may be explained as due to different ordering of Li in the 48f positions. References [1] B. Bajan, G. Balzer, H. J. Meyer, Zeitschrift Fur Anorganische Und Allgemeine Chemie 1997, 623, 1723. [2] A. Kuhn, S. Dill, H.-J. Meyer, Zeitschrift Fur Anorganische Und Allgemeine Chemie 2005, 631, 1565.


11:15 AM PP1.7
Octahedral Metal Clusters as Molecular Building Blocks of Heterotrimetallic Super Expanded Prussian Blue Type Frameworks. Abdou Lachgar, Jian-Jun Zhang, Sergio A Gamboa and Barry J Davis; chemistry, wake forest university, Winston Salem, North Carolina.

The rational design and development of synthetic methodologies toward the assembly of complex crystalline solids with topologies that can to a certain extent be predicted from the structure of the molecular building blocks has achieved tremendous success in different fields of materials chemistry.[1] The approach has been widely applied to the assembly of cyano-bridged materials with diverse structural and physical properties.[2] Among these compounds, the most widely investigated are Prussian blue and its analogues, which constitute a family of complex-based magnetic materials with properties that can be affected through the judicious choice of their molecular building blocks components. Octahedral metal clusters are being investigated as building blocks for a variety of frameworks owing to their large size (~1 nm), their atom-like behavior and their physical properties arisen from the presence of metal-metal bonds. Here we report the preparation and structure of six 3D heterotrimetallic frameworks built of three pre-built molecular building blocks: octahedral cyanochloride clusters ([Nb6Cl12(CN)6]4- or [Ta6Cl12(CN)6]3-, (Mn(salen))+ and mononuclear cyanometallate complexes ([Fe(CN)6]4-, [Cr(CN)6]3-, [Fe(CN)5(NO)]2-, [Ni(CN)4]2-). 3D coordination frameworks are self-assembled at room temperature from solutions containing the building blocks leading to formation of crystals suitable for single crystal X-ray diffraction. The materials crystallize in a distorted face centered cubic framework that can be considered as super-expanded Prussian blue analogue built of two different cyanometallate nodes connected by insertion of (Mn(salen))+ complex. [3] The materials represent the first successful attempt to incorporate mononuclear cyanometallate complexes and cyano-functionalized octahedral metal clusters into the same framework. Details on the synthesis, crystal structures, magnetic properties and thermal behavior of these materials are presented. [1] (a) Robson, R.; Abrahams, B. F.; Batten, S. R.; Gable, R. W.; Hoskins, B. F.; Liu, J. Supramolecular Architecture; ACS: Washington, DC, 1992; Chapter 19. (b) Holliday, B. J.; Mirkin, C. A. Angew. Chem., Int. Ed. 2001, 40, 2022. (c) Yaghi, O. M.; Li, H. L.; Davis, C.; Richardson, D.; Groy, T. L. Acc. Chem. Res. 1998, 31, 474. [2](a) Sieklucka, B.; Podgajny, R.; Przychodzen, P.; Korzeniak. T. Coord. Chem. Rev. 2005, 249, 2203. (b) Beltran, L. M. C.; Long, J. R. Acc. Chem. Res. 2005, 38, 325. (c) Miller, J. S.; Manson, J. L. Acc. Chem. Res. 2001, 34, 563. (d) Dunbar, K. R.; Heintz, R. A. Prog. Inorg. Chem. 1997, 45, 283 [3]Zhang, J-J.; Lachgar, A. “Supra-expanded Prussian-Blue Analogue with [Fe(CN)6]4-, [Nb6Cl12(CN)6]4-, and [Mn(salen)]+ as Building Units.” J. Am. Chem. Soc. 2007, 129(2), 250-251.


11:30 AM PP1.8
New Low Temperature Routes to Iron Sulfides. Nathalie M Pedoussaut and Cora Lind; Chemistry, The University of Toledo, Toledo, Ohio.

Low temperature synthetic pathways can result in crystallization of metastable materials. These methods have been widely explored for the preparation of metal oxides. Adaptation of non-hydrolytic sol-gel chemistry to non-oxide systems offers an elegant route to transition metal sulfides. This method has been exploited for the facile and reproducible synthesis of iron sulfide crystallizing in the troilite structure. This phase is only found in meteorites and planets, and has previously been obtained by high-temperature or high-energy ball milling methods. “Non-hydrolytic” sol-gel processing results in direct crystallization of troilite with no need for further calcination. The samples are slightly iron deficient compared to generally accepted troilite compositions. Heat treatment results in conversion to a pyrrhotite structure of similar stroichiometry.


11:45 AM PP1.9
Synthesis and Characterization of a Novel Maghemite-type Material: γ-Fe2-xCrxO3(0.75 ≤ x ≤ 1.25). Marco Garcia-Guaderrama1, Angel M Arevalo-Lopez1, O. Blanco2, Emilio Moran1 and Miguel Alario-Franco1; 1Facultad de Quimica, Universidad Complutense, Madrid, Spain; 2Centro de Investigacion en Materiales, Universidad de Guadalajara, Guadalajara, Mexico.

Iron sesquioxide shows two well known phases, designated as α-Fe2O3 (the mineral hematite: a classic dark-red pigment with the corundum type structure showing antiferromagnetic properties) and γ-Fe2O3 (the mineral maghemite: a well known ferrimagnetic recording material with a spinel deficient structure). On the other hand, Cr(III) does not seem to form but the α-Cr2O3 form (the mineral eskolaite: a green pigment and useful catalyst which is also another interesting antiferromagnet). Attempts to prepare the γ-form inevitably give the highly stable corundum-type phase1,2 . Interestingly, and on line with other corundum type oxides, the α-forms are fully miscible so that by a solid state reaction, one can obtain the full range of the solid solution α-Fe2-xCrxO3(0.0 ≤ x ≤ 2.0)3, where the magnetic properties change due to changes in the atomic coupling below the Neel temperature4. By means of the Solution Combustion Synthesis (SCS) procedure, we have been able to prepare the title solid solution for the indicated composition range around the1:1 mixed oxide: namely γ-Fe2-xCrxO3 (0.75 ≤ x ≤ 1.25). Beyond this range, hematite and eskolaite, respectively, impurify the reaction product, which is only pure within the indicated range. X-ray diffraction clearly shows the dimensional evolution of the unit cell as a function of the chromium content, while neutron diffraction, as a function of the temperature, illustrates marked variations in the intensity of the diffraction peaks due to the appearance of a magnetic structure at low temperatures. No ordering of the metallic cations appears to be there,since as the presence of chromium increases, the (ferrimagnetic) moment of γ-Fe2-xCrxO3 decreases. In the present communication, we will describe in detail the results for the above solid solution and, in particular, the crystal and magnetic structures. 1.- S. Musić, M. Lenglet, S. Popović, B. Hannoyer, I. Czakó-Nagy, M. Ristić, D. Balzar and F Gashi. 1996. J. Mater. Sci.31:4067-4076. 2.- S. Musić, S. Popović and M. Ristić. 1993. J. Mater. Sci.28:632-638. 3.- T. Grygar, P. Bezdička, and E. G. Caspary. 1999. J. Electrochem. Soc. 146:3234-3237. 4.-T. Grygar, P. Bezdička, J. Dfdeček, E. Petrovsky, and O. Schneeweis. 2003. Ceramics - Silikáty 47:32.


 

SESSION PP2: Fe-As Superconductors and Beyond
Chairs: John Mitchell and Janice Musfeldt
Monday Afternoon, December 1, 2008
Back Bay C (Sheraton)


1:30 PM *PP2.1
Electronic Structure, Magnetism and Spin-Fluctuations in Fe-As Based Superconductors. David J Singh1, Igor Mazin2, Michelle Johannes2, Mao-Hua Du1 and Alaska Subedi1; 1Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee; 2Code 6693, Naval Research Laboratory, Washington, District of Columbia.

The discovery of high temperature superconductivity in a rich family of Fe-As based compounds, prototypes LaFeAs(O,F) and (Ba,K)Fe2As2 has led to considerable activity aimed at sorting out the physical properties of these systems as well as in exploring the chemical dependence of the properties. This talk presents results of density functional calculations of the electronic, vibrational and magnetic properties. The electronic structures show a combination of high density of states and low carrier concentrations, with relatively small Fermi surfaces including heavy hole surfaces around the zone center and somewhat lighter electron surfaces around the zone corner. Furthermore, we find that these compounds are either magnetic or very close to magnetism depending on doping level and structure in accord with experimental results. The electron phonon coupling is far too weak to account for superconductivity in the Fe-based materials. We discuss the spin fluctuations and magnetic ground state in relation to superconductivity. This work was supported by the Department of Energy, Division of Materials Sciences and Engineering (ORNL) and the Office of Naval Research (NRL)


2:00 PM *PP2.2
Superconductivity and Spin-density-wave Instability in FeAs-based Systems. Nan Lin Wang, Institute of Physics, Chinese Academy of Sciences, Beijing, China.

Nan Lin Wang Institute of Physics, Chinese Academy of Sciences, P. O. Box 603, Beijing 100190, China. The recent discovery of superconductivity with Tc ranging from 26 to 55 K in layered FeAs-based RFeAsO (R=La, rare earth) and AFe2As2 (A=Ba, Sr, Ca) has generated tremendous interest in the scientific community. Except for relatively high transition temperatures, the Fe-pnictides display many interesting properties. Among others, the presence of competing ordered ground states is one of the most intriguing phenomena. The undoped parent compounds are not superconducting but exhibit resistivity anomalies at certain temperatures. We provide combined evidence from experimental measurements and first-principle calculations showing that the parent compound has a spin-density-wave instability driven by the nesting between electron and hole Fermi surfaces. From optical measurement on BaFe2As2 single crystals, we show that 75-80% conducting carrier density was removed due to the formation of partial energy gaps below SDW transition. Meanwhile, the carrier scattering rate is reduced by more than 90%. This explains why the conductivity is enhanced in the SDW state. For the superconducting samples, s-wave-like pairing gaps are clearly observed from different spectroscopic probes. Work done in collaboration with: J. L. Luo, G. F. Chen, Z. Fang, X. Dai, J. Dong, Z. Li, G. Li, W. Z. Hu, D. Wu, H. J. Zhang, G. Xu. J. Lynn, P. Dai, H. Q. Yuang, J. Singleton, H. Ding.


2:30 PM *PP2.3
Superconducting Gap of Fe Superconductors. TingYong Chen1, Zlatko Tesanovic1, R. Liu2, Xianhui Chen2 and C. L. Chien1; 1Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland; 2Physics, USTC, Hefei, Anhui, China.

A family of new Fe superconductors of LAFeAsO1-xFx, (Ba-K)Fe2As2, and others has been discovered in 2008 that contain the puckered FeAs planes instead of the hallmark CuO2 planes in the cuprate superconductors. Central to any superconductor is the nature of its superconducting gap, its value, its structure if any, its temperature dependence. We used Andreev reflection spectroscopy to investigate the gap of these new Fe superconductors and its temperature dependence, and compared with those measured by other techniques.


3:30 PM *PP2.4
Recent Experimental Results from Oak Ridge National Laboratory on the New Fe-based Superconductors. David Mandrus, Athena S Sefat, Michael A McGuire, Rongying Jin, Brian C Sales, Andrew D Christianson and Mark D Lumsden; Oak Ridge National Laboratory, Oak Ridge, Tennessee.

In this talk a summary of recent experimental work from ORNL on the new layered Fe-based superconductors will be presented, including some of the first neutron scattering results from the Spallation Neutron Source.


4:00 PM *PP2.5
Neutron Studies of the Iron-based Family of High Tc Magnetic Superconductors. Jeff Lynn, NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland.

We discuss our recent neutron scattering investigations of the crystal structures, magnetic structures, spin dynamics, and lattice dynamics, of the iron-based ROFe(As,P) (R=La, Ce, Pr, Nd) [1] and (Ba,Sr,Ca)Fe,2As2 [2] superconductors. All the undoped materials exhibit universal behavior, where a tetragonal-to-orthorhombic structural transition occurs between ~100-200 K, below which the systems order antiferromagnetically. The magnetic structure within the a-b plane consists of chains of parallel Fe spins that are coupled antiferromagnetically in the orthogonal direction, with an ordered moment typically less than one Bohr magneton. Hence these are itinerant electron magnets, with a spin structure that is consistent with Fermi-surface nesting, along with possible strong electron correlations. The rare-earth moments order antiferromagnetically at low T, like ‘conventional’ magnetic-superconductors. With doping, the structural and magnetic transitions are suppressed in favor of superconductivity, with transition temperatures up to 55 K. The application of pressure in CaFe2As2 transforms the system from a magnetically ordered orthorhombic material to a ‘collapsed’ non-magnetic tetragonal system which is superconducting at a relatively lower T. We will discuss our results of the spin and lattice dynamics for a number of these materials. Further information can be found at http://www.ncnr.nist.gov/staff/jeff [1] C. de la Cruz, et al., Nature 453 , 899 (2008); T. M. McQueen, et al., Phys. Rev. B78 , 024521 (2008); Y. Qiu, et al., Phys. Rev. B78 (in press); Y. Chen, et al., Phys. Rev.B78 (in press); Y. Qiu, et al., arXiv.org/abs/0806.2195; J. Zhao, et al., arXiv.org/abs/0806.2528; Q. Huang, et al., Phys. Rev. B78 (in press); J. Zhao, et al., arXiv.org/abs/0807.4872; S. Chi, et al., arXiv.org/abs/0807.4986. [2] Q. Huang, et al., arXiv.org/abs/080; J. Zhao, et al., arXiv.org/abs/0807.1077; A. Kreyssig, et al., arXiv.org/abs/0807.3032.


4:30 PM *PP2.6
C12A7 Electrides: First S-band Superconductor and Low Work Function Metal with Chemical Stability. Hideo Hosono, Tokyo Institute of Technology, Yokohama, Japan.

C12A7 Electrides: first s-band superconductor and low work function metal with chemical stability Hideo HOSONO Electride is a crystal in which electrons serve as anions. First electride was reported by Prof. James Dye in 1983 using organic complexants. Although this finding stimulated interest of many researchers, application as materials as well as fundamental property research encountered experimental difficulties, materials were only stable at low temperatures in O2/moisuture-free atmosphere. We reported a RT-stable electride using a refractory crystal C12A7. C12A7 electride has the chemical formula of [Ca24Al28O64]4+(4e-) and obtained by substituting all O2- ions in the sub-nanometer--sized cages of 12CaO.7Al2O3 (C12A7) in the crystal structure by electrons. The resulting C12A7 electride exhibits metallic conduction with a conductivity of 1,500 Scm-1 at RT and undergoes superconducting transition at 0.2-0.4K. Since the electron is populated in the cage, this may be regarded as an s-band superconductor. It is a well known that typical s-band metals such as alkaline metals do no exhibit superconducting transition at an ambient pressure. It is thus that C12A7 electride is a first s-band superconductor under an ambient pressure. Another unique property of C12A7 electride is very low work function (2.4 eV). Materials with low work functions (ΦWF) are generally reactive and unstable, and thereby their applications in practical devices are limited. Thus, exploration of low ΦWF materials satisfying these requirements leads to a drastic improvement of electron emission devices and current-injection optoelectronic devices such as OLEDs. Here we report that a new type of inorganic electride, which is chemically and thermally stable, has a small intrinsic ΦWF of ~ 2.4 eV, which is comparable to those of alkali metals. The primary origin of the low ΦWF comes from the occupation of “cage conduction bands (CCB)” with “anionic electrons”, which lifts the Fermi level (EF) ~ 5.5 eV higher from the valence band maximum (VBM). A bias(Vbias)-induced ΦWF shift to even negative is observed on freshly prepared surfaces by ultraviolet photoelectron spectroscopy. Its origin is attributed to a Vbias-induced band bending in an electron-deficient layer inevitably formed at the surface of the nanoporous crystal structure of C12A7. This material is applicable to various types of displays utilizing the exceptional features of small work function and chemical inertness.: cold electron emitter in FED, secondary electron emitter in PDP, cathode material in OLED. Demonstration of each display device is to be presented.


 

SESSION PP3: Poster Session: Oxides and Superconductors
Monday Evening, December 1, 2008
8:00 PM
Exhibition Hall D (Hynes)


PP3.1
Abstract Withdrawn


PP3.2
Phase Transition and Electron Density Distribution in High-Tc Superconductor LaFeAsO1-xFx. Takatoshi Nomura1, SungWng Kim1, Yoichi Kamihara2, Masahiro Hirano2, Peter V Sushko3, Kenichi Kato4, Masaki Takata4, Alexander L Shluger3 and Hideo Hosono1,2; 1Materials and Structure Laboratory, Tokyo Institute of Technology, Yokohama, Japan; 2ERATO-SORST, JST, in Frontier Research Center, Tokyo Institute of Technology, Yokohama, Japan; 3London Center for Nanotechnology & Department of Physics and Astronomy, University of College London, London, United Kingdom; 4RIKEN SPring-8 Center, Hyogo, Japan.

The discovery of high-Tc superconductor cuprates had triggered exploration of new high-Tc superconductors containing 3d transition metal elements, resulting in the enhancement of Tc up to ~140 K and findings of new superconductors containing transition metals other than copper. However, the high-Tc superconductivity is limited to the CuO2 unit and the higher Tc superconductors have not been discovered more than 10 years. February this year, our group found a new iron-based superconductor, LaFeAsO [1], which is constructed by alternatively stacked LaO and FeAs layers and belong to tetragonal (P4/nmm) symmetry at room temperature. Although undoped LaFeAsO does not show any superconductivity, partial substitution of O site with F, which introduces electron careers to the FeAs layer, makes the material a superconductor with Tc ~26 K. The Tc is further increased up to ~55 K by the external pressure and the replacement of La with other rare earth elements such as Sm and Nd [2,3]. It is noteworthy that undoped LaFeAsO shows resistivity anomalies at around 160 K (Tanom), which disappears by the F-doping. No such features have been observed in low-Tc superconductors including LaFePO (Tc ~5 K) and LaNiAsO (Tc ~2 K), indicating the anomaly is closely related to the appearance of the high-Tc superconductivity. In this study, we perform low-temperature crystal structure analysis of undoped and F14%-doped LaFeAsO using the synchrotron powder X-ray diffraction, demonstrating the undoped LaFeAsO shows tetragonal (P4/nmm) to orthorhombic (Cmma) crystallographic phase transition at the Tanom, while the F-doped sample keeps the tetragonal symmetry down to 25K. The electron density distributions in these crystals were also estimated by Maximum Entropy Method (MEM)/Rietveld anlaysis. We will discuss differences of the crystal structures and the electron density distributions between undoped and F-doped LaFeAsO, and also refer the origin of the transition with an aid of the ab-initio calculation results. [1] Y. Kamihara et al., J. Am.Chem. Soc. 130, 3296 (2008). [2] H. Takahashi et al., Nature 453, 376 (2008). [3] Z. A. Ren et al., Chin. Phys. Lett. 25, 2215 (2008).


PP3.3
Abstract Withdrawn


PP3.4
Ion Exchange and Hydration in the Superconducting β-Pyrochlores MOs2O6.nH2O (M= K, Na, Li). Rosa Galati and Mark T Weller; School of Chemistry, University of Southampton, Southampton, Hampshire, United Kingdom.

KOs2O6 belongs to the β-pyrochlore family and has been intensively studied since the discovery of its superconductive nature, Tc~10 K [1]. The KOs2O6 β-pyrochlore structure consists of a three-dimensional network of OsO6 octahedra which, sharing vertices, results in large cavities wherein K+ ions are accommodated. The ability to exchange the M-type in pyrochlores is well known and lead to application for example in nuclear clean-up. Thus the ion exchange of K+ by smaller cations such as Li or Na has been investigated with the aim of synthesizing compounds which cannot be obtained by direct synthesis. The effect of replacing the "rattling" potassium ions on the structures and superconducting properties of these β-pyrochlores has also been studied. New materials, K1-xNaxOs2O6 and K1-xLixOs2O6 with the β-pyrochlore-type structure have been synthesized together with hydrated derivatives K1-xMxOs2O6.nH2O.Parent materials were obtained by ion exchange in non-aqueous solvents under strictly dry conditions. Crystallographic studies using a combination of X-ray and neutron powder diffraction data have been carried out on both dry and hydrated phases to determine the distribution of cations within the pyrochlore channels and the effect of inserted water on this distribution. These structural descriptions are correlated with the measured superconducting properties and theoretical descriptions of variations in the Tc in these systems as a function of cation size and rattling. [1] Yonezawa, S.; Muraoka, Y.; Matsushita Y.; Hiroi, Z. J. Phys. Soc. Jpn., 2004, 73(4), 819.


PP3.5
Preparation and Characterization of Epitaxial Perovskite Manganese Oxide Film Grown by ELAMOD. Tetsuo Tsuchiya, Tomohiko Nakajima and Toshiya Kumagai; National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan.

Perovskite manganese oxide has been a great interest in these materials on both fundamental and practical aspects. The CMR make these materials good candidates for magnetic random access memory and read-head applications. In addition, these materials present a high temperature coefficient of resistance (TCR) at the Curie temperature (Tc) and then can be used as infra-red detectors However, in the case of using PLD or other methods, an epitaxial LSMO film was prepared by the heat treatment at more than 750°C. Therefore, to prepare the LSMO film on Si substrate, it is necessary to lower the processing temperature. To overcome these problems, we have investigated the excimer laser assisted metal organic deposition (ELAMOD) process for the preparation of the metal oxide film at low temperature, and successfully obtained polycrystalline TiO2, In2O3, PbTiO3 and epitaxial PZT film without heating the substrate [1, 2,]. In a previous study, the epitaxial LSMO film on SrTiO3 (STO) substrate was prepared by ELAMOD at a fluence of 80mJ/cm2 with heating 500°C and the TCR of the films showed 4.0% [3]. However, a maximum temperature(Tm) of the TCR was about 275K. Therefore, in this paper, to improve the Tm and TCR of the film, we investigated the effects of the oxygen content and the metal composition on the Tm and TCR from the viewpoint of solid state chemistry. After the oxygen annealing of the as-prepared film for 24h, the TCR of the film decreased from 4.0% to 3.4% at 275K. In the case of the re-irradiated by using the same conditions, the TCR of the film increased 4.0% at 275K. These results mean that oxygen reduction of the film would be effective for the improvement of the TCR of the film. To improve the Tm of the film, we tried to prepare the epitaxial La1-xSrXMnO3(X=0.3) film on STO substrate by ELAMOD. Tm of the film shifted to 293K. However, the TCR of the LSMO(X=0.3) film showed 2.0%. On the other hand, when the La content decreased, the La0.7Sr0.2MnO3 film on STO substrate by ELAMOD showed the maximum TCR of 4.3% at 298K. Detailed procedures of film preparation and the other results such as MR properties will be presented in the paper. [1] T. Tsuchiya, A. Watanabe, Y. Imai, H. Niino, I. Yamaguchi, T. Manabe, T. Kumagai and S. Mizuta: Jpn. J. Appl. Phys. 38 (1999) L1112. [2] T. Tsuchiya, A. Watanabe, H. Niino, I. Yamaguchi, T. Manabe, T. Kumagai and S. Mizuta, Appl. Surf. Sci. , 186 (2002) 173. [3] T. Tsuchiya, T. Yoshitake, Y. Shimakawa, I. Yamaguchi, T. Manabe, T. Kumagai, Y. Kubo and S. Mizuta, Mat. Res. Soc. Symp. Proc. 811, (2004) 419-424.


PP3.6
Abstract Withdrawn


PP3.7
Synthesis and Structure of Perovskite and Perovskite-related Oxyfluorides under High Pressure and Temperature. Tetsuhiro Katsumata1, Mamoru Nakashima1, Hiroshi Umemoto1, Shunpei Suzuki1, Masashi Yoshida1, Yoshiyuki Inaguma1 and Takao Tsurui2; 1Department of Chemistry, Gakushuin University, Tokyo, Japan; 2Institute for Materials Research, Tohoku University, Sendai, Japan.

A stability of the crystal structure of perovskite-type oxides is usually discussed using a tolerance factor. In the case of perovskite-type oxyfluorides, however, the torelance factor does not seem to be always useful. In previous studies, the syntheses of PbFeO2F, BaFeO2F and KTiO2F under high pressure and temperature have been reported.[1] Assuming that the average ionic radius of anions is 1.38Å, the tolerance factors of PbFeO2F, BaFeO2F and KTiO2F are estimated to be 1.00, 1.04 and 1.07, respectively. While the structure is usually cubic for 0.9<t<1.0 for the oxides, these are tetragonal, cubic and cubic for PbFeO2F, BaFeO2F and KTiO2F, respectively.[1,2]. In this study, we tried to synthesize perovskite-type oxyfluorides, PbM3+O2F (M3+=Al, Ga, In, Sc, Ti, V, Cr, Mn and Fe) under the high pressure (≤7 GPa) and temperature, and discussed the stability of the perovskite-type structure of these oxyfluorides. The perovskite phase was obtained for PbMO2F (M=Sc, Cr, Mn and Fe). No perovskite phase was obtained for other compounds. The tolerance factors of PbMO2F (M=Sc, Cr, Mn and Fe) are in the range from 0.93 to 1.02, which seems to be reasonable. On the other hand, PbGaO2F was not be synthesized under this synthesis condition in spite of the tolerance factor of 1.01. Furthermore, the unique super structure were observed for PbMO2F (M=Mn and Fe). According to their tolerance factor (t=1.00 for PbMnO2F and PbFeO2F), the cubic structure would be stable for both compounds. In addition, such super structure is not observed for BaFeO2F. Therefore, it is expected that the 3d electrons and Pb ion, especially the lone pair of Pb ion, play an important role for the stabilities of the crystal structure of these oxyfluorides. Furthermore, we successfully synthesized novel Ruddlesden-Popper compounds, Pb3M3+2O5F2 (M=Cr and Mn) and compare the crystal structures with analogous oxides. 1. B. L. Chamberland, Mat. Res. Bull., 6 , 311, (1971), I. O. Troyanchuk et al, Inorg. Mater., 30 , 920 (1994), I. O. Troyanchuk et al.,Mater Res. Bull., 30 , 421 (1995). 2. T. Katsumata et al., Mater. Res. Soc. Symp. Proc., 988 , 0988-QQ06-03 (2007).


PP3.8
RGB Luminescence in Rare Earth Doped CaZrO3 with Perovskite Structure. Kazushige Ueda, Sho Sakagami and Yuhei Shimizu; Department of Materials Science, Kyushu Institute of Technology, Kitakyushu, Japan.

Pr doped CaTiO3 or Pr-Al codoped SrTiO3 are known as red luminescent perovskite-type oxides. However, luminescent colors and luminescent materials in perovskite-type oxides have been very limited so far. Recently, alkaline earth stannates with perovskite-related structure were found to show several intense luminescent colors by transition metal or rare earth doping. Because luminescence properties have not been extensively investigated in perovskite-type oxides, the observation of intense luminescence from the stannates, as well as the titanates, may bring about a new function in perovskite-type oxides in addition to other well-known functions such as ferroelectricity, piezoelectricity, and superconductivity. In the study of the photoluminescence properties of the perovskite-type stannates, it was suggested that the crystal structural distortion of host lattices is one of key factors that determine PL intensity. The increase of the crystal structural distortion, in other words, the decrease of local symmetry around rare earth ions seems to enhance the PL intensity in rare earth doped perovskite oxides. CaZrO3 forms perovskite-type sturucture as well as CaSnO3 and its structure is more distorted than that of CaSnO3. Therefore, it was anticipated that CaZrO3 has the potential for a favorable host lattice of phosphors. Intense RGB photoluminescence under ultraviolet excitation was observed by Eu-Mg codoping or Tb-Mg codoping into CaZrO3. The RGB tricolor was obtained from a single host lattice of perovskite-type CaZrO3 by just varying a doped rare earth ion and its concentration. Red luminescence was observed in Eu-Mg codoped CaZrO3, and Green and Blue luminescence was observed in Tb-Mg codoped CaZrO3. The color of the luminescence in Tb-Mg codoped CaZrO3 changed with Tb concentration due to the cross relaxation in Tb ions; green color was seen at high Tb concentration and blue color at low concentration. In comparison with other perovskite host lattices, these codoped zirconates showed more intense luminescence than stannates. In addition, Mg codoping with the rare earth ions markedly increased the luminescence intensity. It is considered that the intense luminescence in the zirconates is attributed to large crystal structural distortion of CaZrO3 and local lattice distortion enhanced by Mg substitution at Ca sites.


PP3.9
Two-Step Intercalation Route to New Double and Triple-Layered Perovskites. Jong-Lak Choi and John B Wiley; Department of Chemistry and Advanced Materials Research Institute, University of New Orleans, New Orleans, Louisiana.

Dion-Jacobson (D-J) double and triple-layered perovskites, A[An-1'BnO3n+1] (A = alkali metal, A' = alkaline or rare earth, B = transition metals), have attracted much attention due to their versatile soft-chemistry (e.g., ion-exchange or intercalation). The compound RbLaNb2O7 , for example, can readily undergo ion exchange with other alkali metal cations, H+, NH4+ and Ag+, as well as reductive intercalation with alkali metals to form the corresponding Ruddlesden-Popper (R-P) A2LaNb2O7 compounds. In this study, we have examined the use of a two-step intercalation process with double and triple layered perovskites, A[An-1'BnO3n+1] (A = alkali metal series, A' = Ca or La, B = Nb or Ta), involving reductive alkali-metal intercalation followed by oxidative intercalation with chlorine gas. This approach leads to a series of new oxyhalides that contain alkali-metal halide layers sandwiched between perovskite blocks. Details on the synthesis and the characterization of these compounds, including structural features, will be presented and their thermal stabilities discussed.


PP3.10
Topochemical Manipulation of a Series of Ruddlesden-Popper Layered Perovskites. Elisha Josepha and John B Wiley; Chemsitry and Advanced Materials Research Institute, University of New Orleans, New Orleans, Louisiana.

Topotactic methods allow for the formation of new compounds while maintaining salient structural features. Greaves et al. have shown that it is possible to topochemically intercalate fluorine in the cationic layers between perovskite blocks, as in the formation of the compound Sr3Ru2O7F2 from Sr3Ru2O7. Following their approach, we have investigated the oxidative intercalation of chlorine into a series of Ruddlesden-Popper (RP) compounds with formula An+1MnO3n+1 (A = rare earth, alkaline earth; M = transition metal; n = 1, 2) using several sources of chlorine. Details on the synthesis and characterization of the final compounds An+1MnO3n+1Clx will be presented and the ability to manipulate these products topochemically will be discussed.


PP3.11
Thermal Stability of Metastable Dion-Jacobson Double-Layered Perovskites. Andrew T. Hermann1 and John B Wiley1,2; 1Chemistry, Univ. of New Orleans, New Orleans, Louisiana; 2Advanced Materials Research Institute, University of New Orleans, New Orleans, Louisiana.

The thermal stability of the Dion-Jacobson-related double-layered perovskites, ALaM2O7 (A = H, Li, Na, Ag) (M = Nb, Ta) and (M’Cl)LaM2O7 (M’ = Cu, Fe) (M = Nb, Ta), were investigated. These compounds are made by ion exchange reactions that start with RbLaM2O7 (M = Nb, Ta). While it is known that each of these compounds in both series is metastable above 600° C, details on all these decompositions have not been reported. Here we use variable temperature X-ray powder diffraction and differential scanning calorimetry to examine the decomposition reaction pathways of these materials. Thermal data will be presented and possible reaction pathways discussed.


PP3.12
New Molten-salt Synthesis of Half-metallic Double Perovskite Oxides. Lindsay C. Fuoco and Paul Maggard*; Chemistry, North Carolina State University, Raleigh, North Carolina.

The half-metallic, double perovskites, Sr2FeMO6 (M = Re, Mo), have been synthesized via a new molten-salt synthetic approach. Each metal-oxide can be prepared in a molten KCl/NaCl flux at 750° C in evacuated fused-silica ampoules in reaction times as short as 3 hours. The synthetic conditions were varied in order to investigate the effects of the flux: product molar ratio (1:1, 3:1, 5:1, 10:1, and 20:1) and reaction times (1 h, 3 h, 6 h, 12 h and 24 h) upon the product purity, particle sizes, and their intergrain tunneling magnetoresistance. Use of molten-salt fluxes allows for the control of Sr2FeMO6 particle sizes and morphologies, and the magnitude of the intergrain tunneling has also been shown to be particle dependent.


PP3.13
Abstract Withdrawn


PP3.14
A2MnRuO6 Perovskites: Robust Orbital and Spin Order in Chemically Disordered Double Perovskites. Rebecca A Ricciardo1, Patrick M Woodward1, Adam Hauser2, Fengyuan Yang2, Qingdi Zhou3 and Brendan Kennedy3; 1Chemistry, The Ohio State University, Columbus, Ohio; 2Physics, The Ohio State University, Columbus, Ohio; 3Chemistry, The University of Sydney, Sydney, New South Wales, Australia.

The double perovskites containing Mn and Ru are attractive materials for studying magnetic and electronic properties in transition metal oxides. Sr2MnRuO6 exhibits antiferromagnetic behavior, TN ≈ 200 K, which is stabilized by orbital ordering and is a relatively good electronic conductor, σ298K ≈ 102 Ω-1cm-1. Substitution of La3+ for Sr2+, in part, causes loss of orbital ordering and a structural change from tetragonal to orthorhombic. Additionally, this substituted perovskite exhibits ferromagnetic behavior with TC ≈ 220 K. To further investigate the origin of this ferromagnetic behavior, structural or electronic, a substitution of isovalent Ca2+ in place of Sr2+ in Sr2MnRuO6 is explored. The smaller Ca2+ cation reduces the tolerance factor and induces a change in the octahedral tilt system from a°a°c- (I4/mcm) to a-b+a- (Pnma), as was seen with La3+ substitution. The additional tilting of the octahedra in Ca(2-x)Sr(x)MnRuO6 forces a loss of orbital ordering for x ≤ 1.6, accompanied by a crossover to a ferromagnetic ground state with Curie temperatures between 200 K and 300 K. Structural characterization, magnetic and electrical properties of LaSrMnRuO6 and Ca(2-x)Sr(x)MnRuO6 are discussed in detail. An intriguing facet of these systems is the observation of long range magnetic order in the absence of Mn/Ru chemical order.


PP3.15
Temperature-dependent Studies on the Crystal Structure and Physical Properties of PrCo1-xNixO3 Mixed-valence Oxides. Rosa Robert1,2, Myriam H Aguirre1, Maria Teresa Fernandez-Diaz2, Juan Rodriguez-Carvajal2 and Anke Weidenkaff1; 1Empa-Materials Science & Technology, Duebendorf, Switzerland; 2Institut Laue Langevin, Grenoble, France.

LnMO3 oxides with perovskite structure, where Ln3+ is a trivalent rare-earth ion and M3+ is a trivalent 3d transition-metal ion, represent a fascinating family of compounds due to their potential applications in the fields of e.g. thermoelectricity, catalysis, oxide fuel cell electrodes and magneto-resistance devices. The LnCoO3 system is particularly interesting because it exhibits remarkable transport and magnetic properties as a result of thermally induced spin state transitions in the trivalent cobalt ions. Also the rare-earth nickel oxides which show a complex electronic and magnetic phase diagram [1]. LnNi1-xCoxO3 mixed-valence oxides exhibit ferromagnetic interactions and some of them giant magnetoresistive effects [2]. Recently, cobalt oxides have attracted increasing attention for thermoelectric applications since they show semiconducting or metallic electric conductivity and large thermopower S [3-5]. In this paper, we report on the effect of Ni substitution on the Seebeck coefficient (S) and heat and electric transport properties of polycrystalline PrCo1-xNixO3 (0.3 < x < 0.7) phases prepared by soft chemistry. The advantages of soft chemistry approach compared to the conventional solid state reaction method are a high purity, a lower reaction temperature (T = 873 K), a shorter heating time, and an enhanced ability to control particle size. We have evaluated the crystal structure, morphology and physical properties in the PrCo1-xNixO3 phases upon Ni substitution. Cp measurements performed by DSC evidence a reversible endothermic event occurring at high temperature for all the studied compositions which is associated to an anomaly in resistivity and S values. The increase of Ni content decreases the transition temperature. TGA reveal that this event is not related with weight losses. In-situ high-temperature-dependent (300 K ≤ T ≤ 1173 K) neutron diffraction (HTND) studies reveal that a phase transition occurs from orthorhombic system to a lower symmetry crystal structure. HTND studies are intended to establish a correlation between crystal structure and thermoelectric properties observed in the PrCo1-xNixO3 phases. [1.] Pérez-Cacho J., Blasco J., García J., and Stankiewicz J., Phys. Rev. B, 59 (1999) 14424-14431. [2.] Pérez J., García J., Blasco J., and Stankiewicz J., Phys. Rev. Lett., 80 (1998) 2401. [3.] Terasaki I., Sasago Y., and Uchinokura K., Phys. Rev. B, 56 (1997) R12 685-R12 687. [4.] Maignan A., Hébert S., Pelloquin D., Michel C., and Hejtmanek J., J. Appl. Phys., 92 (2002) 1964-1967. [5.] Yamaguchi S., Okimoto Y., Taniguchi H., and Tokura Y., Phys. Rev. B, 53 (1996) R2926-R2929.


PP3.16
Anomalous Valence of Trinuclear [Mo3] Clusters Embedded in a Solid-state Framework of Mn2Mo3O8. Hideki Abe, Akira Satoh, Naohito Tsujii and Masahiko Shimoda; NIMS, Tsukuba, Japan.

Inorganic compounds containing transition-metal clusters are of growing importance as catalysts for industrial synthesis of organic materials. Oxo- or sulfo-complexes incorporating trinuclear Mo clusters, [Mo3]12+Mn+X2-4 (X = O or S; M = Cu+ or Ni2+), indeed, are one of the most prevailing Lewis-acid catalysts. The catalytic activity of [Mo3]12+Mn+X2-4 is mainly attributed to the metal ions, Mn+. The [Mo3]12+ clusters simply play a role of the building block that do not contribute to catalysis. A [Mo3]12+ cluster possesses a couple of molecular orbitals with either A1 or E1 symmetry, which consist of the 4d-orbitals of the three Mo4+ ions. The six 4d-electrons of a [Mo3]12+ cluster are accommodated by the bonding A1- and E1- molecular orbitals to form a highly stable electronic structure. The [Mo3]12+ clusters are hardly capable to interact with external chemical species to catalyze any reactions, since they are a sort of "closed-shell molecules". A series of mixed-metal oxides, T2Mo3O8 (T = Mg, Zn, Mn, Fe, Co, Ni or Cd), are of interest in terms of the [Mo3] clusters embedded in a solid-state framework. On the basis of X-ray diffractometry (XRD) on single crystals, magnetization measurements, electron spin resonance (ESR) and X-ray photoemission spectroscopy (XPS), we demonstrate that the [Mo3] clusters in Mn2Mo3O8 have an anomalous valence of +10 instead of their normal value of +12. In Mn2Mo3O8, the [Mo3]10+ clusters are energetically preferred than [Mo3]12+ as the result of a strong Jahn-Teller effect around the Mn3+ ions. The [Mo3] clusters in T2Mo3O8 (T = Mg, Zn or Co), in contrast, take the normal valence of +12. A [Mo3]10+ cluster in Mn2Mo3O8 has two excessive electrons relative to the normal [Mo3]12+ clusters. The excessive electrons are adopted by a non-bonding A1-molecular orbital of the [Mo3]10+ cluster to form an unshared electron pair. Unlike any known [Mo3]-containing compounds, Mn2Mo3O8 has a potential as a Lewis-base catalyst, due to the existence of unshared electron pairs that are localized on the [Mo3] clusters.


PP3.17
Synthesis of Materials in the AA’M3O12 Family using a Non-Hydrolytic Sol-Gel Process. Tamam Issa Baiz and Cora Lind; Chemistry, The University of Toledo, Toledo, Ohio.

Negative thermal expansion (NTE) materials, which shrink upon heating, have been a topic of great interest in recent years. Incorporating NTE compounds into composites will allow the synthesis of materials with more desirable expansion coefficients. Through this approach, a mismatch of thermal expansion between bonded materials, which could result in cracks, stresses or separation, can be avoided. One family of materials that has been known to show NTE is the A2M3O12 family, where A can be a variety of trivalent cations and M is Mo or W. However, little research has been carried out on systems containing two differently charged cations instead of just trivalent cations. In the research presented here, the target is the development of systems where the A site contains two differently charged ions, leading to the synthesis of materials of the type AA’M3O12 (A= Mg, Zn; A’= Zr, Hf). Previously, tungstate systems of this type have been explored via a ball-milling technique, followed by high temperature treatments. Reported herein are the results of a study aimed at synthesizing these materials using a much lower temperature route, known as the non-hydrolytic sol-gel method (NHSG). This allows access not only to the tungstates, but also to the corresponding molybdates. Samples were characterized using variable temperature powder X-ray diffraction and scanning electron microscopy.


PP3.18
Preparation of the (SnPb0.4In0.6)Ba4(Er2.5,Yb2.5)Cu7O20±y, Compound by Solid-state Reaction. Elizabeth Chavira1, Araceli Ordonez1, Leticia Banos1, Omar Novelo1, Esteban Fregoso-Israel1 and Valentin Garcia-Vazquez2; 1Universidad Nacional Autonoma de Mexico, Mexico, Mexico; 2IF Benemerita Universidad Autonoma de Puebla, Puebla, Mexico.

Our interest to work on (SnPb0.4In0.6)Ba4(Er2.5,Yb2.5)Cu7O20±y, compound generate with the announcement of the report of the first observation of superconductivity over 180 K superconductor. We prepared by solid-state reaction. After heating the mixture of the policrystalline material was analyzed by thermogravimetric analysis, observing the changes of weight (0.25%) in 268 °C, we attribute to the superficial water and (92%) at 798 - 950 °C to the formation of different compounds. The formation of diverse compounds and structure, were confirm by X - ray diffraction powder (XRD). We reacting the sample in the interval from ambient temperature until 950 °C. We detected that the sample at ambient conditions dehydrated very quickly. Then we have to take care with the humidity. The XRD analysis (880 - 950 °C) resolute the formation: Ba2Cu3In4O12 (PDF 44-0266), Ba2Cu3ErO7 (PDF 39-1404), BaCuYb2O5 (PDF 41-0613), Ba5Cu2YbO8.5 (PDF 45-0673) and Cu2Yb2O5 (PDF 33-0507). By Scanning Electron Microscopy (SEM) we determined the phases observed by XRD, also at 950 °C we observe a semifusion. Then we considerate that is better to decrease the reaction temperature to obtain at ones two phases. We decided to prepare a new compositions: Ba2(Er0.5Yb0.5)Cu3.5O6 and (SnPb0.4In0.6)Ba4(Er4Yb6)Cu7O20 establish by the analysis of EDX. We did not observe the desired 1245/1212 phases reported. This work was partially supported by UNAM-PAPIIT-IN109308.


PP3.19
Hydrated β-pyrochlore Oxide Phases- A2+(TaWO6)2.H2O (Ca, Sr and Ba), A+TaWO6.nH2O ( A = Cs, Rb and K) and Fluoride Analogues. Charles Simon and Mark T Weller; Chemistry, University of Southampton, Southampton, United Kingdom.

The pyrochlore system, with the general formula AnB2X7-x is a key structure type that exhibits a wide range of useful properties including ion exchange, magnetic frustration and superconductivity. β-Pyrochlores, AB2X6, are excellent candidates for applications as ion exchange materials, with a high rates of ion exchange and a considerable degree of control over the pore sizes and thus cations that can be accommodated. Pyrochlore phases, particularly zirconates and titanates, have been used in the disposal of actinides produced by fission as the framework they provide is particularly stable to irradiation thus providing a medium for long term storage1. Here we present recent structural characterisation work on two series of oxide materials, that have excellent ion exchange properties, studying how cation size, charge and levels of hydration influence the distribution of species in the channels and hence control the ion exchange properties. Materials with both mono and divalent A site cations have been synthesised and studied, i.e. A+TaWO6.nH2O (A = Cs, Rb and K) and A2+(TaWO6)2.H2O (A = Ca, Sr and Ba). Materials have been fully structurally characterised using high resolution powder neutron diffraction (PND), which has allowed very accurate structural information to be determined including distribution and orientation of the water molecules within the channels. Such structural detail is essential in understanding ion exchange behaviour and isotherms for the exchangeable ions in aqueous solutions. These phases are of particular interest as barium, strontium and cesium isotopes are all major products of fission with half lives ranging from months to years and are therefore important in the disposal of nuclear waste. Studies of two new phases are also presented, A2+(TaWO6)2.H2O where A = Cd and Pb, increasing the range of materials formed with this structure type through ion exchange reactions; these systems have possible applications in heavy metal waste disposal. A range of metal fluorides adopting the pyrochlore structure have also been studied for comparative purposes, with effects of the position of the cations studied in both hydrated and non-hydrated phases investigated. The use of fluorides and thus lower charged/smaller B site ions allows a broader range of cavity sizes to be observed and allow incorporation of lighter, cheaper metals in the ion exchange materials. (1) Ringwood, A. E.; Kesson, S. E.; Ware, N. G.; Hibberson, W.; Major, A. Nature 1979, 278, 219-223.


PP3.20
Structural and Magnetic Properties of Oxychalcogenide Materials. John Simon Owen Evans and David G Free; Chemistry, Durham University, Durham, United Kingdom.

Oxychalcogenides are materials that contain oxide ions and another group 16 element in the 2- oxidation state. Due to the different bonding requirements of the hard oxide ion and soft(er) sulfide or selenide, such materials often display layered structures and a variety of different structural types are known. In this poster we will present details of members of the [Ln2O2Q2][M2O] family where Ln is a lanthanoid, Q is S or Se and M a first row transition metal. These have structures related to that of [La2O2S2][Fe2O] first reported by Mayer et al (J.M. Mayer, et al, Angewandte Chemie, 1992, 104, 1677) and can be described in terms of face sharing MO2Se4 octahedra separated by Ln2O2 fluorite-like layers. We will report new members of this family and describe their structural and magnetic phase transitions.


PP3.21
When Solid-State Oxide Reactions Involve Liquids. Jessica L. Riesterer1,4, N. Ravishankar2, Jeffery K Farrer3 and C. Barry Carter1; 1Chemical, Materials and Biomolecular Engineering, University of Connecticut, Storrs, Connecticut; 2Materials Research Centre, Indian Institute of Science, Bangalore, India; 3Physics and Astronomy, Brigham Young University, Provo, Utah; 4Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota.

The chemistry of solid ceramics at ambient conditions is generally a result of processing at high temperatures. However, at the processing temperature the presence of impurities and second phases often leads to the formation of a liquid phase that solidifies, and may even crystallize, on cooling. Examples of such a process are the formation of amorphous films at grain boundaries and droplets on surfaces. Exudation of liquids from boundaries during thermal treatment creates interesting solid-state microstructures at the surface on cooling. Since ceramics processed at high temperatures cannot be easily monitored in situ, data must be collected post-processing, when the entire material is in the solid state. In the present study, several oxides have been studied using atomic-force microscopy (AFM) and electron backscatter diffraction (EBSD) to infer the high-temperature behavior from room-temperature observations. By depositing thin films on single-crystal substrates, the same region of sample can be examined using AFM after repeated heat treatments. AFM can similarly be used to examine how liquids move in and out of internal interfaces and how this process affects the resulting microstructure and chemistry. Orientation effects are studied using EBSD.


PP3.22
Sol-Gel Synthesis and Characterization of YAG:Ce Phosphors by Various Pre-firing Temperatures. Kyu-Seog Hwang1, Seung Hwangbo2, Ju-Hyun Jeong3,1, Su-Chang Ahn4 and Youngsik Park4; 1Biomedical Engineering, Nambu University, Gwangju, South Korea; 2Photonic Engineering, Honam Univeristy, Gwangju, South Korea; 3Ophthalmic Optics, Konyang Univeristy, Daejeon, South Korea; 4Micro-Optics Team, Korea Photonics Technology Institute, Gwangju, South Korea.

Ceria doped-yttrium aluminum garnet (Y3Al5O12:Ce, YAG:Ce), which is known as an efficient phosphor, have been widely used in optical display and lighting applications. Improved wet chemical method, sol-gel, has been studied, since conventional solid-state reaction requires a high-temperature and prolonged heating to obtain the pure phase. However, there has been little information, such as on pre-firing temperature, concerning high-quality powder formed by the wet chemical process. In this work, YAG:Ce was synthesized with a salted sol-gel process in which a water solution of inorganic salt with citric acid as additive. Transparent starting sol was pre-fired at 150 ~ 350°C for 2 hrs in air and final annealing to obtain phase-pure YAG:Ce particles was performed at 1100°C for 4 hrs in argon. The effects of pre-firing temperatures on the crystal structure, morphology and luminescence were investigated. Effects of residual organics in the pre-fired gel on the properties of finally annealed phosphors will be fully discussed on the basis of the results of thermal analysis and chemical structure.


PP3.23
Molecular Precursor Routes to Yttrium and Lanthanide Vanadates and Niobates Based on Well-defined EDTA Coordination Compounds. Nicolas Deligne and Michel Devillers; Unité de Chimie des Matériaux Inorganiques et Organiques, Université Catholique de Louvain, Louvain-la-Neuve, Belgium.

Ln-based mixed oxides generate a lot of interest because of their numerous applications in materials science, such as ion conductors, luminescent materials and heterogeneous catalysts. In that context, a great effort is needed to develop new preparation routes able to produce these materials with a high purity under various forms: bulk phases with appropriate morphologies and textural properties, supported phases for catalytic applications and thin films for optical or conductivity applications. This work aims at developing a soft chemistry approach to prepare Ln-based mixed oxides in bulk and thin films forms, and focuses on the consequences of the preparation method on the properties. The method consists in using, for the different elements to be incorporated, molecular precursors which are coordination compounds. The multimetallic oxide materials are obtained by an appropriate thermal treatment in air of a solid homogeneous mixture of the different complexes. For that purpose, EDTA, oxo-EDTA and peroxo-bis-N-oxido-EDTA complexes of general formula (NH4)[LnIII(EDTA)]●xH2O (Ln = Y, Pr, Sm, Eu, Gd, Dy, Er), (NH4)3[VV(O)2(EDTA)]●H2O and (gu)3[NbV(O2)2(EDTAO2)]●2.5H2O (gu = guanidinium) are synthesized, characterized and used as precursors of the multimetallic oxides. Thermal behaviour of the mixed precursors is studied by thermogravimetric analysis and the final oxides are characterized by XRD analysis, Raman spectroscopy, XPS and scanning electronic microscopy. Zircon-type MVO4 hosts are synthesized at a moderate temperature of 800°C, as evidenced by XRD and Raman analyses. Solid solutions such as Y1-xPrxVO4 and Y1-xGdxVO4 are also obtained. Linear correlations between chemical compositions and lattice parameters or Raman shifts are observed. SEM is used to characterize the particle size and morphology. A slightly disordered intergranular porosity is observed. Ln-doped YVO4 are also prepared and their emission spectra are recorded. In the Ln-Nb-O system, a distorted tetragonal form of LnNbO4 is stabilized at room temperature for several Ln3+ ions under optimized conditions. This LnNbO4 polymorph is not accessible by conventional preparation routes as the tetragonal form turns to a monoclinic phase when temperature is raised to room temperature. In 3Ln-Nb-O systems, Raman and XRD analyses indicate the stabilization of pyrochlore type phases Ln3NbO7 and a linear correlation between lattice parameter a and Ln3+ ionic radius is observed. Scanning electron microscopy indicates the formation of mesoporous materials with pore sizes of about 20 nm.


PP3.24
Using XRD and Atomistic Simulation to Determine the Mechanisms of Non-stoichiometry in Yttrium Aluminum Garnet. Ankoor Pankaj Patel1, Chris R Stanek2, Romaine Gaume3, Stephen R Podowitz3, Mark Levy1, Robert S Feigelson3, Ken McClellan2 and Robin W Grimes1; 1Materials, Imperial College London, London, United Kingdom; 2MST-8, Los Alamos National Laboratory, Los Alamos, New Mexico; 3Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California.

Yttrium Aluminium Garnet, (YAG), is a material particularly well suited for application in laser devices (Nd:YAG) and as a scintillator (Ce:YAG and Pr:YAG). The optical properties of this material are generally degraded by the defects present and therefore many studies have been conducted to establish the structure and properties of both the intrinsic and extrinsic defects. In this study, we used a combination of experiment and atomistic simulation to determine the mechanisms of Y2O3 and Al2O3 excess non-stoichiometry. To make this determination, we compared experimentally measured lattice parameters for YAG samples of known deviations from stoichiometry, and compared those results to lattice parameters predicted by atomistic simulation for all possible nonstoichiometric mechanisms. The comparison revealed that the mechanism with best agreement to experimental data corresponded to the mechanism with the lowest predicted reaction energy, namely cation antisites for Y2O3 excess and Al2O3 excess.


PP3.25
Structure-property Relationships in Oxygen Deficient Sillenites. Andrew G. Donovan, Emma E McCabe and Derek C Sinclair; Engineering Materials, The University Of Sheffield, Sheffield, United Kingdom.

LTCC (Low Temperature Co-fired Ceramic) dielectrics are those that can be effectively sintered below 960°C, the melting point of silver. This allows electrodes and associated circuitry to be applied before final densification, resulting in a more compact and rugged final component. One candidate system for this application is the Sillenites (ideal formula Bi12M4+O20). These materials have a cubic structure (space group I23), and are effectively a stabilised form of the metastable γ polymorph of Bi2O3, which is itself only stable between 540 and 600°C. Sillenites have a high permittivity for a compound that forms below 800°C (εr~50), which may make them suitable for use as a LTCC dielectric material for microwave applications. In some cases, they can also exhibit oxide-ion conductivity. In this presentation we discuss the links between the structure and electrical properties of a family of oxygen-deficient Sillenites. Oxygen deficient Sillenite ceramics of the type Bi12(M3+xBi3+1-x)O19.5 where M3+ = B, Al, Ga & In have been synthesised by a mixed oxide route. Isovalent doping of the M site by cations of varying radii and the structural changes associated with this leads to variations in the thermal stability of the Sillenite phase. It has been found that whilst the gallium composition is stable throughout its temperature range and exhibits useful electrical properties, the aluminium and indium samples show structural phase changes upon heating. The indium composition exhibits a reversible change between the Sillenite and δ-Bi2O3 structure, whilst aluminium compositions show more complex irreversible changes.


PP3.26
New High Dielectric Constant, Rare Earth Titanate-Bronzes for Microwave Applications. Yuqi Li and Peter K Davies; Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania.

Ba6-xRE8+2x/3Ti18O54 (RE = rare earth) titanate bronzes have been widely investigated for application as high dielectric constant (εr), temperature stabilized (τf) microwave materials with low dielectric loss ( = high quality factor, “Q”). The highest reported Q values occur in the Nd and Sm systems for x=0.67, where εr ~ 80, Q ~ 2000-3000 @ 2-3 GHz and τf = ± 5ppm/C. In this paper we report on new modifications of these solid solutions where the goal was to increase the Q.f value to 10,000-15,000 for applications at 0.4-1 GHz and simultaneously reduce the overall rare-earth content. The structure of Ba6-xRE8+2x/3Ti18O54 is comprised of a “Ti18O54” framework that hosts two types of sites for the barium and RE cations. Four larger sites have pentagonal bipyramidal coordination; ten smaller sites have a so-called rhombic coordination and the structural formula can be described as {(Pentag)4(Rhomb)10}Ti18O54. While the structure is usually referred to as a titanate-bronze, it is more rigorously described in terms of an ordered intergrowth of tetragonal tungsten bronze lamellae (2[A2A’B5O15]) and perovskite slabs (8[A’BO3]). In the compositions reported to show the highest Q’s (Ba4RE9.33Ti18O54) each structural site is occupied by a single type of cation: the pentagonal positions by Ba and the rhombic sites by the smaller RE cation. However, the chemical composition requires partially occupancy of the rhombic positions by 0.67 vacancies. The first part of this talk will focus on elimination of the cation vacancies in Ba4RE9.33Ti18O54 via the coupled replacement of Nd and vacancies by Ca (2Nd3+ + vacancy = 3Ca2+). Single-phase bronzes with Ba4{Nd9.33-2xVac0.67-xCa3x}Ti18O54 could be prepared for 0≤x≤2/3 and the dielectric properties of the new x = 2/3 end-member (Ba4{Nd8Ca2}Ti18O54) will be reported. We will also report on additional reductions in the rare-earth content through the partial substitution of Ti4+ by Nb5+. Niobium substitutions have never been examined in these systems and there are no reports of how they affect the dielectric constant or the loss. Single phase samples could be formed in the vacancy-free Ba4{RE8-xCa2+x}(Ti18-xNbx)O54 and vacancy-containing Ba4{RE9.33-xCax}(Ti18-xNbx)O54 systems for Nb contents up to at least x = 3. Preliminary measurements of the dielectric properties revealed the incorporation of Nb increases the permittivity to εr ~ 100. Results for the microwave properties will be also presented and discussed.


PP3.27
Microstructure and Phase Behavior in Ni-Ti-O System. Sanjit Bhowmick, Jessica L Riesterer, Jonathan Winterstein and C. B Carter; Chemical, Materials and Biomolecular Engineering, University of Connecticut, Storrs, Connecticut.

Samples containing NiTiO3 (ilmenite) and NiO are being studied as a model porous system for investigating phase evolution and precipitate formation at different annealing temperatures by combining AFM, EBSD and TEM. Interesting geometrical patterns of precipitates are observed after heating the samples above 1000 °C. XRD and EDS indicate the appearance of nickel oxide precipitates in the surrounding matrix of NiTiO3 and Ni2TiO4 (spinel structure). AFM and EBSD reveal that the precipitates may have plate- or needle-like shape, and they are aligned parallel to specific planes of the crystals of matrix forming a Widmänstatten-like structure. The crystallographic orientation and structure of the precipitates are studied by TEM, which also allows elemental mapping and selective analysis to determine, in detail, the chemical composition of the precipitates and adjacent areas. In situ heating experiments in the TEM are being carried out to examine possible mechanisms and kinetics of nucleation and growth of the precipitates. A statistical analysis on the number, size, shape and, in particular, the width of the precipitates as a function of annealing temperature and time will also be considered.


PP3.28
NaOH and KOH Flux Growth of ZnO and Mn-Substituted ZnO. Chun-Min Feng, Daniel Margul and Glen R. Kowach; Chemistry, The City College of New York, New York, New York.

Single crystal growth of pure zinc oxide (ZnO) and manganese-substituted zinc oxide (Mn-substituted ZnO) is demonstrated in various fluxes including boron oxide (B2O3), potassium hydroxide (KOH), and sodium hydroxide (NaOH). Compared to crystal growth from the B2O3 flux, which leads to plate-like morphology, the NaOH flux yields hexagonal prismatic morphology of ZnO and Mn-substituted ZnO crystals. For NaOH flux grown crystals, a non-uniform distribution of Mn substitution was found in the ZnO single crystals in the range of approximately 0 at.% to 0.25 at.% for an initial concentration of 35 at.% of Mn in the flux. In addition, polycrystalline Mn-substituted ZnO powder was prepared by solid state synthesis using manganese oxide (Mn2O3) in order to investigate the distortion of the lattice and the effect on magnetic properties. The unit cell volume of polycrystalline ZnO increases with increasing manganese content from 47.75(3) Å3 (ZnO starting material) to 48.093(3) Å3 (Zn0.945Mn0.055O) for Mn concentrations from 0 at.% to 5 at.%. At a Mn concentration of 5.46 at.%, the formation of ZnMn2O4 was minutely observed, and for greater initial quantities of Mn2O3 the amount of ZnMn2O4 increased. From SQUID magnetometer studies, Mn-substituted polycrystalline ZnO is paramagnetic down to 5 K; no room temperature ferromagnetism is observed.


PP3.29
Fabrication of Textured Bulk Hematite by Slip Casting in a Strong Magnetic Field. Naoki Nakamura1, Tetsuo Uchikoshi2 and Yoshio Sakka2; 1Advanced Material Engineering Division, Toyota Motor Corporation, Susono, Shizuoka, Japan; 2Nano Ceramics Center, National Institute for Materials Science, Tsukuba, Ibaraki, Japan.

As a common fundamental technology, it is important to establish a manufacturing process to obtain nano-structure controlled thin films or bulk materials retaining starting material's nano-structures (size and alignment) and their properties. It is a dream for material engineers to make high-functional and intelligent materials only using the "ubiquitous element" such as iron, oxygen, aluminum and silicon, which have high Clarke number and high availability. Texture control in bulk materials is one of promising approaches to fabricate advanced materials with high anisotropic functionalities considering the cost, productivity and technical viability. In this study, we focused on controlling the nano-structure of iron-based material and clarifying the relationship between the controlled textile structures and their magnetic properties. Aligned bulk hematite was successfully prepared by using magnetic alignment and topotactic transformation. In order to avoid agglomeration due to magnetic interaction between ferromagnetic hematite nanoparticles, we used diamagnetic goethite nanoparticles as the starting material. The stable colloidal suspension of goethite was consolidated to a bulk by slip casting under a magnetic field of 2 - 12 Tesla. SEM & XRD results show that the short axis (a-, b-axis) was aligned along the magnetic field due to the anisotropic susceptibility of goethite. The obtained goethite green body was then sintered at 900 - 1200 degrees centigrade external to the magnetic field, resulting in a topotactic transformation of goethite into hematite. SEM & XRD results show that the transformed bulk hematite was aligned with c-axis along the direction of the magnetic field, which was applied during the slip casting. Compared with these results, it was found that the a-, b- axis of goethite was transformed into c-axis of hematite. The degree of orientation of bulk hematite improved with the increase of sintering temperature and entirely aligned bulk hematite was obtained at 1200 degrees centigrade. Magnetic hysteric measurements by VSM show that the magnetic hysteresis matches with its anisotropy structure. The remanent magnetization and coercivity are 0.229 emu/g and 620 Oe in easy axis of magnetization and 0.018 emu/g and 913 Oe in hard axis of magnetization. Magnetic anisotropy increased with the increase of structural anisotropy of bulk hematite.


PP3.30
Synthesis and Properties of Magnetite Powders. Amy C Marschilok3,2, Shali Zhu1, Kenneth J. Takeuchi1 and Esther S Takeuchi3,2,1; 1Chemistry, University at Buffalo, Buffalo, New York; 2Chemical and Biological Engineering, University at Buffalo, Buffalo, New York; 3Electrical Engineering, University at Buffalo, Buffalo, New York.

The preparation of magnetite powders by a co-precipitation method will be described. Results from x-ray powder diffraction measurements will be presented, including crysallite size estimates using the Scherrer equation. Also particle size distribution data will be presented. As part of the presentation, an interesting relationship among reactant concentrations, crystallite sizes, and particle sizes will be discussed.


PP3.31
Study of [Cr-O6] Based Rutile Derivatives by Means of EELS. Angel M Arevalo-Lopez, Elizabeth Castillo-Martinez, Carlos Rodriguez-Hernandez and Miguel Alario-Franco; Facultad de Quimica, Universidad Complutense, Madrid, Spain.

The rutile structure, with an MO2 stoichiometry is a rather common one among transition metal oxides, with a relatively small ionic size, 0.4Å < r < 0.8Å. Although the basic structure is tetragonal, S.G. P42/mnm, different distortions appear for a variety of reasons, indicating it to be a rather versatile structure-type . We present in here the study by means of EELS of several rutile based oxydes, having in common the presence of octahedral chromium in three different oxidation states: Cr4+ in CrO2, a regular rutile1 ; Cr3+ in CrOOH2 , a H bonded orthorrombic distorted rutile and CrTaO4, a metal disorder rutile3 and finally Cr2+ in CrTa2O6 an order trirutile structure4. An interesting relation is observed between the formal oxidation state of chromium in the different oxides and the separation between the Cr-L3 and O-K energy loss peaks. 1.- Porta P., Marezio M., Remeika J.P., Dernier, P.D. Materials Research Bulletin 7, 1972, 157-162. 2.-Alario-Franco M.A., Sing, K.W. J. Thermal Analysis 4,1972, 47-52. 3.-Massard P., Bernier J.C., Michel A. Journal Solid State Chemistry 4, 1972, 269-274. 4.-Saes, M., Raju, N.P., Greedan, J.E. Journal Solid State Chemistry 140, 1998, 7-13.


PP3.32
Using Aberration-Corrected HAADF Imaging to Develop Structural Models for Multicomponent Mo-V-M-O (M=Nb or Ta, Te) Complex Oxide Catalysts. William D Pyrz1, Douglas A Blom2, Vadim V Guliants4, Thomas Vogt3 and Douglas J Buttrey1; 1Center for Catalytic Science and Technology, Department of Chemical Engineering, University of Delaware, Newark, Delaware; 2NanoCenter and Electron Microscopy Center, University of South Carolina, Columbia, South Carolina; 3NanoCenter and Department of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina; 4Department of Chemical and Materials Engineering, University of Cincinnati, Cincinnati, Ohio.

In our work, we use high-angle annular dark-field (HAADF) STEM imaging to develop preliminary structural models for several Mo-V-M-O (M=Nb or Ta, Te) complex oxide catalysts used for the selective oxidation of light alkanes. Current processes used to produce high-demand C3 derivatives, namely acrylic acid and acrylonitrile, require the use of multicomponent bismuth molybdates with propene as the feed [1-2]. Significant cost savings can be achieved by replacing propene with propane. Top candidates for this replacement are based on the multiphase Mo-V-O based materials and the best current formulation is the MoVTeNbO complex oxide system [1-2]. The optimal MoVTeNbO catalysts with respect to selectivity and activity are two-phase mixtures comprised of an orthorhombic network bronze (M1) and a hexagonal tungsten bronze (HTB)-type phase (M2) [1-2]. By using HAADF imaging and applying the Z-squared contrast approximation [3-4], we are able to evaluate several catalyst formulations and estimate the chemical composition of individual atomic columns, the atomic coordinates of the metal framework, and the occupancy of the intercalation species enclosed within polyhedral rings [5]. Using the structural models for several different Mo-V catalyst formulations, we can begin to develop structure-property relationships that connect catalytic performance to trends in crystal structure, active site composition, or the inclusion/exclusion of various substitutional elements. Furthermore, these HAADF-derived models can be developed in short periods of time (~1-2 weeks) and can serve as starting models for rigorous refinements that otherwise may require several months or even years to complete due to difficulties in estimating the large number of parameters necessary for full structure refinement. Rapid evaluation of complex catalyst formulations can assist with efficient assessment of relationships between crystal chemistry, structure, and catalyst performance. References: [1] R. K. Grasselli, Top. Catal. 21 (2002) 79. [2] P. DeSanto et al., Z. Kristogr. 219 (2004) 152. [3] A. Howie, J. of Microscopy-Oxford 117 (1979) 11. [4] E. Abe et al., Nature, 421 (2003) 347. [5] W. D. Pyrz et al., Angew. Chem., Int. Ed. 47 (2008) 2788.


PP3.33
Lowering of Soot Combustion Temperature by Silver-Delafossites. Yuya Toyoda1, Satoru Matsuishi2, Hideo Hosono1,2,3 and Yasushi Hayashi4; 1Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama, Kanagawa, Japan; 2Frontier Research Center, Tokyo Institute of Technology, Yokohama, Kanagawa, Japan; 3ERATO-SORST, Japan Science and Technology Agency, Kawaguchi, Saitama, Japan; 4Corporate R&D Department, DENSO CORPORATION, Kariya, Aichi, Japan.

Recently, diesel engine cars have become more popular than gasoline engine ones owing to the better fuel efficiency, low operating cost and high durability; however they often generate pollutant exhaust gases containing NOx, SOx and soot. Pt/CeO2 catalysts have been widely investigated to combust soot with oxidative power of NOx, but there have been many issues. e.g. Pt/CeO2 catalysts need NOx for combustion and are expensive. A silver ion and its compounds are also known as combustion catalysts, e.g. Ag/Al2O3 catalysts burn soot with ethanol at ≧336 oC(1); however there have many issues too. Silver and its compounds are deteriorated by reacting with SOx to form silver sulfide by repetition use and need ethanol or NOx. In this work, we explored silver-delafossites as combustion catalysts for soot without NOx. Delafossite-type crystals have a chemical compositions of ABO2 (A = Ag, Cu, B = Al, Ga, In) and its crystal structure is composed of alternate stacking of A layers and edge-sharing BO6- octahedral layers. Here Ag+ ions are constituents of crystal structure and tend to displace to interstitial postions of AO-layers. We expect that such features are favorable for suppression stabilization of silver sulfide formation and enhance the catalytic activity. AgAlO2 was synthesized by the hydrothermal method, where a mixure of Ag2O and NaAlO2 powders was put into water in an autoclave, followed by heating at 200 oC for 48h. Products precipitated were washed by a NH3 aqueous solution to remove residual Ag2O. Phase purity was characterized by XRD. Their catalytic activities with soot were examined by TG-DTA-Mass in an ambient atmosphere without NOx. Catalyst poisoning was tested by the TG-DTA-Mass analyses and the XRD after putting it into a 1N sulfuric acid aqueous solution and ultrasonic agitation for 3 minutes at room temperature. For comparison, AgGaO2 and AgInO2 were synthesized from Ag2O, Ga2O3, and In2O3 by the hydrothermal method with a 1N NaOH aqueous solution at 200 oC for 48h. It was found that the starting combustion temperature was lowered from 450 oC to 280 oC by AgAlO2 catalyst without ethanol nor NOx. The usage of AgGaO2 and AgInO2 further reduced to 240 oC. The low starting combustion temperature remained unchanged even after catalyst poisoning test. We speculate that Ag0 atoms were temporally formed in the interstitial position when heated, and the resulting Ag0 atom is responsible for the strong catalytic activity. The replacement of Al3+ ions with larger Ga3+ and In3+ ions would enhance the formation of interstitial Ag0 atoms at lower temperatures, resulting in the lowering of the combustion temperature. (1)Hongyi Dong, Shijin Shuai, Rulong Li, Jianxin Wang, Xiaoyan Shi, Hong He, Study of NOx selective catalytic reduction by ethanol over Ag/Al2O3 catalyst on a HD diesel engine, Chemical Engineering Journal, 135 (2008) 195-201.


PP3.34
Synthesis of Hydrogen Titanium Oxide Hydrate using a Low Temperature Solution Process for the Application of Photo-Catalysis. Yu Hua Cheng and Zhong Chen; School of Materials Science and Engineering, Nanyang Technological University, Singapore, Singapore.

In this study, a low temperature solution route has been employed to produce hydrogen titanium oxide hydrate. The solution underwent hydrothermal treatment at a series of temperatures. Transmission Electron Microscopy (TEM) and X-ray Diffraction (XRD) were employed to study the crystal structure and morphology of the nano-powders. Density Functional Theory (DFT) calculation was also performed to provide a theoretical model of the material's crystal structure. Large surface area was determined by the Brunauer Emmet and Teller (BET) technique. Photo-catalytic tests were performed by degrading Methylene Blue dye under light irradiation. The material displayed exceptional performance in dye degradation in comparison to an industrial titanium oxide photo-catalyst powder, Degussa P25. The photo-catalytic performance of the titanium hydrate material varies with synthesis conditions, and this brings about an interest in the factors that governs and tailors the unique properties of such a material. The understanding of synthesis factors can greatly help in improving the efficiency of materials for the growing applications of photo-catalysis.


PP3.35
Interlayer Surface Modification of Layered Niobate with Phenylphosphonic Acid. Yumi Kato1, Akira Shimada1, Seiichi Tahara1, P. Hubert Mutin2 and Yoshiyuki Sugahara1; 1School of Advanced Science and Engineering, Waseda University, Tokyo, Japan; 2UMR CNRS 5637, Université Montpellier 2, Montpellier, France.

Interlayer surface modification of layered niobate with phenylphosphonic acid was achieved by reaction between the intercalation compound (C12H25NH3)xK4-xNb6O17, derived from layered niobate K4Nb6O17 and phenylphosphonic acid. X-ray powder diffraction (XRD) analysis showed that the interlayer distance decreased from 3.43 to 2.02 nm. The solid-state 13C CP/MAS NMR spectrum of the product showed that signals due to phenyl group were present and that the intensities of the signals due to n-dodecylammonium ions drastically decreased. The solid-state 31P MAS NMR spectrum revealed the signal due to phenylphosphonic acid shifted upfield upon reaction. Scanning electron microscopic observation demonstrated that plate-like morphology was maintained through the reactions. These results suggest the occurrence of the interlayer surface modification with phenylphosphonic acid.


PP3.36
Swelling of Layered Potassium Ruthenate into Nanosheet Crystallites. Wataru Sugimoto1,2, Hisato Kato1, Katsutoshi Fukuda2 and Yoshio Takasu1; 1Textile Science and Technology, Shinshu University, Ueda, Nagano, Japan; 2Nano-FIC, Shinshu University, Ueda, Nagano, Japan.

Layered potassium ruthenate is a unique material with mixed conductivity and finds use as electrode material for electrochemical capacitors and fuel cells. In this study, the swelling behavior of layered potassium ruthenate was studied. The layered potassium ruthenate is extremely hydroscopic and immediately absorbs water from the atmosphere. The as-prepared protonated form has a composition of H0.2RuO2.1-0.9H2O with an interlayer spacing of ~0.78 nm. The monohydrate undergoes dehydration into H0.2RuO2.1-0.5H2O when left standing for prolonged time under atmospheric conditions. Despite the lower hydration state, the lowest angle diffraction peak shifts to lower angle. Heat treatment at 453 K leads to complete dehydration to a phase with an interlayer spacing of 0.45 nm. Reaction of the monohydrate phase with aqueous tetrabutylammonium hydroxide (TBAOH) results in the formation of TBA-ruthenate intercalation compound. The dried materials do not directly react with TBAOH, and one must use intermediates in order to introduce TBA into the interlayer. The swelling behavior is strongly dependent on the ratio of the TBA cation and the ion-exchangeable proton. At an optimized ratio, total exfoliation is achieved. The resultant nanosheets were characterized by synchrotron in-plane XRD and AFM.


PP3.37
Ion-exchange Reactions of Layered Aluminophosphate. Masato Mesaki, Fumiaki Tando, Seiichi Tahara and Yoshiyuki Sugahara; School of Advanced Science and Engineering, Waseda University, Tokyo, Japan.

Ion-exchange reactions of layered aluminophosphate [AlPO4(OH)](C6H5C2H4NH3) was performed between C6H5C2H4NH3+ and organoammonium ions (n-propylammonium, n-butylammonium, and n-hexylammonium ions). The products were characterized by XRD, SEM and 13C CP / MAS NMR. Upon reactions with n-propylammonium, n-butylammonium, and n-hexylammonium ions, XRD patterns showed that the interlayer distance changed from 1.97 nm to 1.66 nm, 1.86 nm, and 2.26 nm, respectively; the interlayer distance increased as the length of n-alkyl chains increased. Upon the reactions, 13C CP / MAS NMR showed signals assignable to C6H5 group disappeared and signals assignable to n-alkyl chains appeared. Furthermore, SEM images showed platy morphology, which is similar to that of starting [AlPO4(OH)](C6H5C2H4NH3). These results demonstrate that [AlPO4(OH)](C6H5C2H4NH3) exhibited ion-exchange properties.


PP3.38
The Effect of Cr2O3/ZnO on Hydrogen Desorption Properties of MgH2. Aep Patah1, Akito Takasaki1 and Janusz S Szmyd2; 1Regional Environment System, Shibaura Institute of Technology, Tokyo, Japan; 2AGH-University of Science and Technology, Krakow, Poland.

Some metal oxides, in no doubt, give catalytic effects to improve the kinetics of hydrogen absorption and desorption of magnesium hydride (MgH2) after mechanical milling (MM). The addition of oxides has mainly been performed by single oxide such as Nb2O5 or Cr2O3. The effect of addition of more than one oxide at the same time, however, has not yet been reported. We investigated the effects of addition of 1 mol% zinc oxide (ZnO) and/or 1 mol% Cr2O3 on the hydrogen desorption properties of magnesium hydride. The desorption temperature of hydride were examined by Differential Scanning Calorimeter (DSC) after MM process. A total milling time of MM, performed in an argon gas atmosphere, was 20 hours, and milling speed was 400 rpm. Addition of single oxide separately gave the hydrogen desorption temperature of MgH2 to ~362 °C and to ~360 °C for MgH2/1.0mol% Cr2O3 and MgH2/1.0mol% ZnO, respectively. The hydrogen desorption temperature of MgH2 decreases to ~347 °C after combined addition of two kinds of oxides. Most of MgH2-oxides powders showed double hydrogen desorption peaks in DSC curves. Furthermore, after a certain threshold MgH2-oxides composition, the desorption temperature of the peak doublet changed gradually to single peak with increasing the amount of ZnO. It was also observed by X-ray diffraction measurement (XRD) that the double hydrogen peak corresponded to the presence of two polymorphic forms of magnesium hydride, β- and γ-MgH2 after MM. Addition of single ZnO has caused a single desorption peak, indicating that ZnO reduces the amount of γ-MgH2 phase, which is known as a metastable high-pressure phase, produced during MM process. XRD also showed that the presence of ZnO after dehydrogenation was significantly reduced. Apparently, addition of 1mol% ZnO together with 1mol% Cr2O3 helps to reduce hydrogen desorption temperature of MgH2 by about 30 °C compared to that of MgH2 without any oxide. A synergetic effect is believed to be occurred after addition of two kinds of oxides. Some mechanisms, one of which is thought to be a solid solution reaction of Zn into Mg during heating, could probably decrease the hydrogen desorption temperature of MgH2. ZnO, however, is also thought to act as a catalyst which makes their surfaces available for hydrogen chemisorbed process. The role of both the kind of oxides (Cr2O3/ZnO) and the duality of hydride phases (β- and γ-MgH2) in hydrogen desorption process to help the improvement of absorption/desorption kinetics of MgH2 is also discussed.


PP3.39
Fabrication of Electrically Active Si-based Thin Films by Pulsed Laser Deposition of SiO/C Dual Targets. Yusaburo Ono1, Yasuyuki Akita1, Yushi Kato1, Makoto Hosaka1, Makoto Yamaguchi2 and Mamoru Yoshimoto1; 1Department of Innovative and Engineered Materials, Tokyo Institute of Technology, Kanagawa, Japan; 2R and D Department New Process Development Group, Sumitomo Titanium Co., Ltd., Hyogo, Japan.

Development of semiconductor electronic device field is attributed to great progress of science and technology using Si-based materials. For example, Si materials have already been applied for solar cell and integrated circuit. Furthermore, SiO2 materials have been used as insulation (amorphous SiO2) and piezoelectric materials (quartz SiO2), etc. On the other hand, few research on the electrical activation of oxygen-deficient SiOx has been made in the past. As SiO is a insulating, amorphous and sublimation material, SiO materials have often been used as antireflection and barrier films, etc. Possibility of SiO as electronic function materials is not necessarily studied enough. So far, we have examined fabrication of the Si nanocrystals embedded in the SiOx thin films by pulsed KrF excimer laser (wavelength of 248nm, duration time of 20ns) annealing of the SiOx thin films, which were prepared by pulsed laser deposition (PLD) method using SiO ceramics target. The obtained thin films were found to exhibit strong photoluminescence at room temperature. In this work, we attempted to fabricate thin films with novel electronic functions by applying laser ablation process using the dual targets of SiO and C. The role of C is considered to accelerate a chemical reaction which produces nano crystalline SiC or Si during annealing SiO/C multi layered thin films. The thin films were fabricated on quartz glass at room temperature by PLD method. The fabricated thin films were characterized X-ray diffraction (XRD), laser microscope, transmissivity and I-V measurement. The obtained thin films were amorphous. The optical band gap of SiO thin films was calculated from transmissivity measurement to be approximately 3.2eV. SiO/C multi layered thin films were fabricated and then were annealed in Ar atmosphere. These annealed films exhibited much lower resistivity, and showed the photo-electric property when solar light were irradiated.


PP3.40
Atomic Layer Deposition of NiO on Oxide and Metal Substrates. Erik Lindahl, Mikael Ottosson and Jan-Otto Carlsson; Department of materials chemistry, Uppsala University, Uppsala, Sweden.

Nickel oxide has been deposited by Atomic Layer Deposition (ALD) by the use of Bis(2,2,6,6-tetramethyl-3,5-heptadionato)Ni(II) (Ni(thd)2) and water precursor combination. The stability of the metal precursor which is vital in ALD has been studied and restricts ALD deposition of NiO to 275°C. The film growth follows ALD characteristics as the growth is self limiting in each step. In the used temperature range the contamination of carbon, originating from the organic ligand of the metal precursor, shows values of maximum 3% as measured by x-ray photo electron spectroscopy. The initiation of the growth has been studied by atomic force microscopy and reveals a preferred growth on already nucleated NiO on silicon oxide substrates. Grazing incidence x-ray diffraction of films deposited on platinum substrates shows formation of an interphase layer closest to the substrate with a shift in lattice constant compared to the rest of the film and reported bulk lattice constants for NiO.


PP3.41
Exploring the Potential for New Calcium Phosphates. Matthew Cave1, Colin Slater1, Liam M Grover2 and Adrian Jerome Wright1; 1Chemistry, University of Birmingham, Birmingham, United Kingdom; 2Chemical Engineering, University of Birmingham, Birmingham, United Kingdom.

The inherent biocompatibility of calcium phosphates means they have significant potential as biomaterials. However, the range of calcium phosphate structures known is relatively limited and has been established for some considerable time. The most widely employed bioceramic phase is hydroxyapatite (Ca10(PO4)6(OH)2), but although this phase is closely related to bone mineral, it does possess poor resorption characteristics. Therefore there is a need to provide alternatives that can better match the required characteristics for applications such as hard tissue replacement, bone cements and drug delivery media. There is also potential to form hybrid materials that may complement polymer matrices to provide access to novel nano-composite materials. We report here a series of new calcium phosphates materials with diverse structures ranging from relatively dense crystalline materials, through inorganic-organic hybrids, to amorphous phases. A particularly significant group are the calcium condensed phosphates, including calcium polyphosphates (Ca(PO3)2), which offer the added presence of P-O-P linkages, similar to motifs essential to vital biologically functions such as mammalian energy transfer (ATP/ADP) and DNA formation. Consequently, many biological systems possess enzymes which manipulation these P-O-P linkages and thus these materials have the potential to offer enhanced resorption. We report on our initial investigations into these properties. A range of inorganic-organic hybrids are also presented which possess simple organic molecular fragments separating the calcium phosphate inorganic layers, and their structures are fully described. We also report the isolation and detailed characterisation of a number of amorphous calcium phases, including a series of amorphous calcium pyrophosphates (Ca2P2O7.nH2O), amorphous calcium triphosphate carbonates and amorphous calcium polyphosphate materials.


PP3.42
Transferred to PP4.3

PP3.43
Molten-Salt Synthesis of New Fresnoite-type Magnetic Insulators: A2MnV2O7Cl (A= Rb, Cs) and Ba2Mn(Mn2-xSix)O7Cl (x = 0.6, 2.0). K.G. Sanjaya Ranmohotti, Xunhua Mo, Shiou-Jyh Hwu and Wendy L Queen; Department of Chemistry, Clemson University, Clemson, South Carolina.

Garnet (A3B2B’3O12), perovskite (ABO3), pyrochlore (A2B2O7) and spinel (AB2O4) are technologically significant structure types adopted by a vast number of complex oxides of optical, electronic, and magnetic importance. Despite the inherent noncentrosymmetric (NCS) structure of fresnoite type compounds, synthetic exploration in this system has not matched that of these well-known metal oxides. The fresnoite mineral, Ba2TiSi2O8 (BTS), can be denoted as the A2BO(B’2O7) type (A = Ba2+; B = Ti4+; B’ = Si4+). The structure consists of two-dimensional B-O-B’ oxide sheets made up of alternating TiO5 square pyramids and Si2O7 pyrosilicate units that share corner oxygen atoms. The vertex oxygen of the TiO5 units and barium cations occupy the space between the adjacent oxide sheets. The fresnoite family is steadily attracting more attention due to rich structural chemistry, observed through multiple cation substitution, and piezoelectric and pyroelectric properties. The anion substitution in the fresnoite-type solids was first reported by us in the recently discovered chlorosilicate Ba2Mn(Si2O7)Cl compound. Four new NCS compounds having the Cl--substituted fresnoite structure were isolated in reactive molten-salt media. In these structures, the oxo-oxygen is substituted by chlorine due to the inclusion of the molten salt: A2MnCl(V2O7) (A= Rb 1, Cs 2) and Ba2MnCl(Mn2-xSixO7) (x = 0.6 3, 2.0 4). Crystals of 1~4 have been grown in a eutectic flux of RbCl/KCl, CsCl/KCl, and BaCl2/NaCl. In each case the larger of the two electropositive cations employed in the flux is incorporated into the structure. These compounds crystallize in a tetragonal lattice, P4bm (No. 100), with a = 8.5-9.2 Å, c = ~5.4 Å, V = 390-463 Å3; Z = 2. In the structures of 1 and 2, the Ti4+ site (2a) is occupied by Mn3+, while the Si4+ (4c) site is replaced by V5+ ions. The characteristic pentagonal windows consist of the O-O edges of three VO4 tetrahedra and two MnO4Cl square pyramids. The substitution of the vertex oxygen with the chlorine anion creates short-and-long Mn-Cl--Mn distances allowing further separation between the Mn3+-O-V5+ sheets and electronic confinement of the magnetic spins within the sheets. The temperature-dependent susceptibility data of these magnetic insulators were analyzed based on a two-dimensional model. The intralayer antiferromagnetic coupling decreases with respect to an increase in the separation of the adjacent manganese ions. This is supported by an observed decrease in the magnitude of the calculated theoretical exchange values (-J/k), 8.6(2), 4.7(1), 4.03(9) for compounds 4, 1, and 2, respectively. The oxide-based versatile fresnoite structure encompasses a variety of compositions allowing synthetic chemists the opportunity to tune important physical phenomena and potentially develop new multiferroic materials. In this presentation, detailed structure analysis and structure property correlation studies will be discussed.


PP3.44
Abstract Withdrawn


PP3.45
Dielectric - Spectroscopic Studies on Layered K 1.9Na 0.1Ti4O9 Ceramic. Shripal Sharma1, Dwivedi Shailja2 and Tandon Ram Pal3; 1Shripal, Department of Physis, P.P.N. College, Kanpur-208001, Uttar Pradesh, India; 2Shailja, Department of Physics, P.P.N. College, Kanpur-208001, Uttar Pradesh, India; 3R.P.Tandon, Department of Physics and Astrophysics, Delhi University, Delhi-110007, Delhi, India.

Ceramic samples of layered Na2Ti3O7, K2Ti4O9 and their iron and manganese doped derivatives have been investigated through various studies by Shripal et al. [1-5].Very recently, the presence of different peaks in ε- T plots for Na2-x Kx Ti3O7 with x = 0.2, 0.3, and .4,ceramics [6] were evidenced by different kinds of dipoles relaxation due to manganese substitution at different sites and three types of permanent dipoles in pure sodium titanate [7]. In this communication, the dependence of loss tangent(tanδ) and real and imaginary parts of the dielectric constant (ε’ & ε”) have been reported for layered K1.9 Na0.1Ti4O9 (named PST) ceramic in the temperature range 373K-898K and on frequencies from 40 kHz to 1MHz. The K2Ti4O9 has a zigzag layered structure and is composed of TiO6 octahedra which are so heavily distorted that the position of Ti4+ ion deviates from the center of gravity of surrounding six oxygen ions, thus yielding dipole moment. This suggests that the existence of relaxation peak is due to the dipolar relaxation at lower frequencies and in lower temperature region [8]. From tanδ-T variations, it can be concluded that the losses are of mixed type i.e. dipolar and losses due to the interlayer ionic conduction. The variation of the dielectric constant as a function of temperature at some fixed frequencies and as a function of e∝ has been estimated by extrapolating the ε ’’ vs. ε ‘ plot on the high frequency side (ε∝= 440 ± 5). From the measured values of ε’ and ε’’ and the extrapolated value of ε∝ = 440, the static dielectric constant, εο = 538 best fits the normalized Cole - Cole plot. At 373 K and 423 K the two values are almost same i.e. α = 0.31 ± 0.01 and τ = 30 m Sec. Such a large value of relaxation time may be attributed to the rotation of the molecule as a whole. The relaxation mechanism has also been analyzed corresponding to overall molecular rotation and intra molecular group rotation using Budo’s equation. References: 1) Shripal, Pandey S D, Chand P. Solid State Commun. , 69 (1989) 1203 2) Shripal , Mishra AK ,Pandey SD, Tandon R P ,Eur. J. Solid State Inorg. Chem , 29 ( 1992 ) 229 3) Shripal, Tandon R P, Pandey S D, J.Phys.Chem.Solids, 52 (1991) 1101 4) Shripal, Badhwar S, Maurya D , Kumar J, J. Mater. Sci.: Materials in Electronics 16 (2005) 495. 5) Shripal, Maurya D, Shalini , Kumar J, Mater. Sci. Engg. B, 136 (2007) 5. 6) Maurya D, Kumar J, Shripal, J. Phys. Chem. Solids, 66, (2005) 1614. 7) Ogura S, Sato K, Inoue Y, Phys. Chem, 2 (2000) 2449 8) Bogoroditski, Pasynkov V V, Tareev B, “ Electrical Engineering Materials ”, Mir Pub. Moscow, 1979, P 65.


 

SESSION PP4: Synthesis, Crystal Chemistry and Physical Properties of Oxides
Chairs: Mario Bieringer and Kenneth Poeppelmeier
Tuesday Morning, December 2, 2008
Back Bay C (Sheraton)


8:30 AM *PP4.1
Revisiting the High Pressure Ternary Oxides of Cr(IV): from Perovskites to Misfit Layer Type Compounds. Miguel Alario-Franco, Elizabeth Castillo-Martínez and Angel M Arevalo-Lopez; Facultad de Quimica, Universidad Complutense, Madrid, Spain.

Cr(IV) oxides have recently experienced a kind of revival in view of their very interesting electronic properties: electric transport, magnetic, thermal, etc 1. Apart from the binary oxide, CrO2, a rather unusual high pressure ferromagnetic half metal, there is a limited number of ternary oxides, in particular the simple A(II)Cr(IV)O3, perovskites (A <> Ca, Sr, Pb)2 . We have been studying in detail those oxides as well as the novel solid solution Sr1-xCaxCrO3 and some Ruddlesden-Popper (R&P) phases of general formula Srn+1CrnO 3n+1. In the course of this work we have also been able to discover a novel hexagonal perovskite, 15-R SrCrO3, a compositionally modulated non-stoichiometric perovskite “PbCrO3” as well as several new chromium based misfit layer type (MLT) compounds [SrO]2[CrO2]x. All these phases have been prepared at high pressures (40-80 kbar) and high temperatures (900-1500K)3 and have in common the presence of octahedral oxygen coordinated Cr(IV). Interestingly, in every one of these materials the [Cr-O6] octahedra show a different distortion for each structural type. We are reporting in here our recent results concerning these materials that will be described in order of structural complexity: from the basic perovskites through the more elaborated R&P phases to the complicated modulated and (MLT) ones. Emphasis is given to the structure and the particularly rich microstructure -including microdomais, extended defects and intergrowths-, of the different compounds as obtained from X-ray diffraction and transmission electron microscopy and diffraction, but attention is also given to their interesting -and often controversial- electronic and magnetic properties. The study is complemented with an electron energy loss spectroscopic analysis of the different phases. [1](a) Zhou, J. S.; Jin, C. Q.; Long, Y. W.; Yang, L-X. ; Goodenough, J. B. Phys. Rev. Lett. 2006, 96, 046408 (b) Ortega-San-Martin, L.; Williams, A.J.; Rodgers, J.; Attfield, J.P.; Heymann, G.; Huppertz, H. Phys. Rev. Lett. 2007, 99, 255701 (c) Komarek, A.C. et al. arXiv :0804.1071v1 [cond-mat.str-el] [2] (a) Chamberland, B. L. Solid State Commun. 1967, 5, 663-666, (b) Kafalas, J. A.; Goodenough,J. B.; Longo, J. M. Mat. Res. Bull. 1968, 3, 471 (c) Chamberland, B. L.; Moeller, C. W. J. Solid State Chem. 1972, 5, 39-41. [3](a) Castillo-Martinez, E., Durán, A., Alario-Franco, M.A. J. Solid State Chem. 2008, 181, 895-904. (b) Castillo-Martínez, E., Alario-Franco, M.A. Solid State Sci. 9, 7 2007 564-573 (c) Arévalo-López, A. M.; Alario-Franco, M.A. J. Solid State Chem. 2007, 180, 3271. (d) Castillo-Martínez, E., Schönleber, A., van Smaalen, S., Arévalo-López, A. M., Alario-Franco, M.A., Journal of Solid State Chem. (in the press 2008).


9:00 AM PP4.2
Simultaneous Jahn-Teller Distortion and Magnetic Order in the Double Perovskite Ba2154SmMoO6. Abbie Christina Mclaughlin, Chemistry, University of Aberdeen, Aberdeen, United Kingdom.

The magnetic and structural properties of the double perovskite Ba2154SmMoO6 have been investigated; results from SQUID magnetometry and neutron diffraction on this material will be presented. An unexpectedly high antiferromagnetic transition temperature (TN = 130 K) has been observed as a result of a strong interplay between spin, orbital and lattice degrees of freedom. The crystal structure distorts from tetragonal (space group I4/m) to triclinic (space group I-1) as the temperature is reduced below 353 K. A Jahn-Teller distortion is observed at TN so that a tetragonal elongation of the MoO6 octahedra is evidenced. The results suggest that orbital order precipitates antiferromagnetic order with anomalously high TNs in the 4d1 Mo5+ Ba2REMoO6 (RE = Sm, Eu) double perovskites.


9:15 AM PP4.3
Magnetic Interactions of A-Site Cu2+ Spins in A-Site Ordered Perovskites. Yuichi Shimakawa, Hiroshi Shiraki and Takashi Saito; Institute for Chemical Research, Kyoto University, Uji, Kyoto, Japan.

A series of A-site ordered perovskite CaCu3B4O12 with nonmagnetic B-site ions were synthesized under high pressure conditions. In the compounds, only A-site Cu2+ spins contribute to the magnetic properties and they show very unusual magnetic interactions. Magnetic interactions of Cu2+ (S=1/2) spins in CaCu3Ge4O12 and CaCu3Sn4O12 are ferromagnetic, while that in the isostructural CaCu3Ti4O12 is antiferromagnetic. Either ferromagnetic or antiferromagnetic behavior can thus appear within the same structural framework. In solid solutions of CaCu3Ge4O12 - CaCu3Ti4O12 - CaCu3Sn4O12 the effective magnetic interaction between Cu2+ spins changes gradually and systematically from ferromagnetic to antiferromagnetic to ferromagnetic despite the monotonous increase in Cu-Cu distance. Therefore a simple magnetic interaction cannot explain the behavior and the special alignment of the square coordinated CuO4 units in the perovskite structure plays an important role in the magnetic properties of Cu2+ spins. Direct exchange interaction gives rise to the ferromagnetic behavior in CaCu3Ge4O12 and CaCu3Sn4O12, whereas involvement of Ti-3d orbitals produces the antiferromagnetic superexchange interaction in CaCu3Ti4O12. At intermediate compositions the perfect balance of the competing interactions causes unusual instability.


9:30 AM PP4.4
Structural Diversity in High Pressure Bi[M′1/2M′′1/2]O3 Perovskite Compounds. Matthew R Suchomel, John B Claridge, Mathieu Allix and Matthew J Rosseinsky; Chemistry, University of Liverpool, Liverpool, United Kingdom.

Recent interest in Bi-based perovskite oxides has been motivated by intriguing predictions of multiferroic coupling in Bi-based oxide systems and by the possibility of using Bi-based materials to replace current environmentally unfriendly Pb-containing ferroelectric and piezoelectric materials. The "lone-pair" 6s2 electronic configuration of the Bi3+ cation is similar to that of Pb2+, and often promotes polar structural distortions; while the flexibility of the trivalent B site in the perovskite structure affords the substitution of a wide range of complex combinations of transition metal cations that may promote magnetic and/or ferroelectric responses. In this work, we report on recent developments of new polar and magnetically ordered Bi-based bulk perovskite oxide compounds synthesized by high pressure, high temperature solid state methods. This synthetic approach provides access to many new meta-stable structures which cannot be realized under ambient pressure conditions. The focus of this work is primarily on systems of the general formula Bi[M’1/2M’’1/2]O3, where M’ and M’’ are 2+, 3+, and 4+ transition metal cations. Several compounds with unanticipated structures have been identified in the course of this work; including very tetragonally distorted structures for Bi[Zn1/2Ti1/2]O3 and Bi[Co1/2V1/2]O3 , and orthorhombic incommensurate structures in the compositions Bi[Ni1/2V1/2]O3 and Bi[Co1/2Ti1/2]O3. The physical properties of these new compounds will be reported and discussed. Based on these new examples and previously known Bi-based perovskite compounds, connections can be made between the B site cation chemistry, the observed structural distortions, and the resulting physical properties in these systems.


9:45 AM PP4.5
High Pressure Synthesis and Properties of Late Rare Earth RFeAs(O,F) Superconductors. Jan-Willem Bos1,2, George Penny1,2, Jennifer Rodgers1,2, Dmitry Sokolov1,3, Andrew Huxley1,3 and Paul Attfield1,2; 1Centre for Science at Extreme Conditions, University of Edinburgh, Edinburgh, United Kingdom; 2School of Chemistry, University of Edinburgh, Edinburgh, United Kingdom; 3SUPA, School of Physics, University of Edinburgh, Edinburgh, United Kingdom.

A breakthrough in high temperature superconductivity has recently occurred with the discovery that rare earth oxypnictides RFeAsO (first reported for R = La,Ce, Pr, Nd, Sm and Gd)[1] can show critical temperatures surpassed only by the high-Tc cuprates. The first report of superconductivity was in LaFeAsO1-xFx samples with Tc‘s up to 26 K [2], increasing to 43 K at 4 GPa pressure [3]. Superconductivity has subsequently been induced in the other members of the RFeAsO series using fluoride doping, with ambient pressure Tc’s of 41 K for R = Ce [4], 52 K for Pr [5] and Nd [6], 43-55 K for Sm samples [7], and 36 K for Gd [8]. We are using high-pressure high-temperature synthesis to explore late rare earth analogs of the RFeAsO materials. New TbFeAs(O,F) and DyFeAs(O,F) superconductors have been prepared, with critical temperatures Tc = 46 and 45 K and very high critical fields ≥ 100 Tesla [9]. In this contribution we report the structures and properties of these and other new members of the RFeAs(O,F) superconducting family, and compare them to the earlier R superconductors. references 1 P. Quebe, L. J. Terbuchte and W. Jeitschko, J. Alloys Compounds, 2000, 302, 70. 2 Y. Kamihara, T. Watanabe, M. Hirano and H. Hosono, J. Am. Chem. Soc., 2008, 130, 3296. 3 H. Takahashi, K. Igawa, K. Arii, Y. Kamihara, M. Hirano and H. Hosono, Nature, 2008, 453, 376. 4 G. F. Chen, Z. Li, D. Wu, G. Li, W. Z. Hu, J. Dong, P.Zheng, J. L. Luo and N. L. Wang, Phys. Rev. Lett., 2008, 100, 247002. 5 Z. -A. Ren, J. Yang, W. Lu. W. Yi, G. -C. Che, X. -L. Dong, L. -L. Sun and Z. -X. Zhao, 2008, arXiv:0803.4283. 6 Z. -A. Ren, J. Yang, W. Lu, W. Yi, X. -L. Shen, Z. -C. Li, G. -C. Che, X. -L. Dong, L. -L. Sun, F. Zhou and Z. -X. Xhao, 2008, Europhysics Letters, 82, 57002. 7 X. H. Chen, T. Wu, G. Wu, R. H. Liu, H. Chen and D. F. Fang, Nature, 2008, doi:10.1038/nature07045; Z. -A. Ren, W. Lu, J. Yang, W. Yi, X. -L, Shen, Z. -C. Li, G. -C. Che, X. -L. Dong, L. -L. Sun, F. Zhou and X. -X. Zhao, Chin. Phys. Lett. 2008, 25, 2215; R. H. Liu, G. Wu, T. Wu, D. F. Fang, H. Chen, S. Y. Li, K. Liu, Y. L. Xie, X. F. Wang, R. L. Wang, L. Ding, C. He, D. L. Feng and X. H. Chen, 2008, arXiv:0804.2105. 8 P. Cheng, L. Fang, H. Yang, X. Zhu, G. Mu, H. Luo, Z. Wang and H. -H. Wen, 2008, Science in China G 51(6), 719. 9 J. -W. G Bos, G. B. S. Penny, J. A. Rodgers, D. A. Sokolov, A. D. Huxley and J. P. Attfield. Chem. Comm, 2008 (in press) and arXiv:0806.0926


10:30 AM *PP4.6
Spin-Lattice Interactions Mediated by Magnetic Field. Janice Lynn Musfeldt1, Jinbo Cao1, Luciana Vergara1, Alexander Litvinchuk2, Yongjie Wang3, S. Park4 and Sang Cheong4; 1Department of Chemistry, University of Tennessee, Knoxville, Tennessee; 2Texas Center for Superconductivity and Department of Physics, University of Houston, Houston, Texas; 3National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida; 4Center for Emergent Materials and Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey.

Application of a magnetic field offers an incisive opportunity to tune competing interactions in complex materials. Here, we probe field-induced changes in the local structure of DyMn2O5 using magneto-infrared spectroscopy. The high tunability of the dielectric constant and ferroelectric polarization with field is well documented in the literature, but the lattice response on the microscopic level remains unknown. In this work, we reveal the dynamic nature of the local structural response to field and analyze it in terms of calculated mode displacements and local lattice distortions.


11:00 AM PP4.7
Low Dimensional and Geometrically Frustrated Magnetism in Ordered NaCl-type Oxides. John Greedan1, Shahab Derakhshan1, Heather Cuthbert1 and Lachlan Cranswick2; 1McMaster University, Hamilton, Ontario, Canada; 2Canadian Neutron Beam Centre, Chalk River, Ontario, Canada.

The magnetic properties of multi-component oxides with the ordered NaCl structure are relatively little explored. Two examples will be described. Na3Cu2SbO6 is a recently discovered spin gap material. Site ordering among the Na+, Cu2+ and Sb5+ ions results in a layered crystal structure in which the Cu sublattice forms a distorted honeycomb topology. Nonetheless, the magnetic properties are well described as an alternating linear chain magnet with two principal exchange constants. While it is clear that a spin singlet is the ground state at low temperature, controversy exists regarding the sign of the exchange constants within the chain. Experimental and computational evidence has been presented in favor of both AF/AF and AF/F models. An attempt will be made to resolve this issue. The second example is Li3Mg2RuO6 which crystallizes in Fddd. The Ru5+(S = 3/2) sublattice has an unique topology consisting of ribbons of edge-sharing triangles parallel to [110] crystal directions which share corners along [001], thus, presenting the condition for geometric magnetic frustration. Magnetic susceptibility, heat capacity and neutron diffraction data are consistent with this expectation.


11:15 AM PP4.8
Novel Transition-Metal Sulphates: Synthesis, Structures and Magnetic Properties. Anthony V. Powell, Patricia Leyva-Bailen and Paz Vaqueiro; Chemistry, Heriot-Watt University, Edinburgh, United Kingdom.

Template-directed synthesis is increasingly used in the search for new materials with novel architectures. Synthesis is generally effected under solvothermal conditions in the presence of organic amines. When added to a gel or slurry of reactants, these exert a structure-directing effect on the crystallisation process, leading to inorganic structures, in which the organic species is retained within the channels, cavities or inter-layer spaces. We have recently begun to explore the use of oxy-anions as building blocks for the construction of inorganic frameworks and here present recent results on solvothermally-synthesised transition-metal sulphates. Synthesis in the presence of ethylenediamine, produces [enH2]5[Mn4(SO4)8(H2O)2(OH)2](1 ), the structure of which consists of discrete anions constructed from four edge- and vertex-linked MnO6 octahedra, bridged by sulphate ions. This unit of four metal-centred octahedra serves as the building block for new layered materials in which the tetramers are fused to form chains. In the structure of [NH4]2[Fe3(SO4)3(OH)2(H2O)2](2 ) the chains are cross-linked by sulphate ions to form anionic layers. Charge balancing is provided by ammonium ions that reside in the inter-layer space. Whilst Mn6(SO4)6(H2O)4(tetn)2 (3 ), contains analogous layers, the layers are neutral. These are linked by triethylenetetramine (tetn) molecules, the terminal nitrogen atoms of which are coordinated directly to Mn2+, to generate an unusual organic-inorganic hybrid framework structure. By varying the reaction conditions, we have also succeeded in producing layered variants, M(SO4)(tetn) (M=Mn, Fe) (4 ), (5 ), of these hybrid materials. The structure of (4 ) and (5 ) consists of inorganic chains in which sulphate ions are coordinated to the metal centres. The chains are cross-linked into neutral layers by triethylenetetramine, the nitrogen atoms of which complete the octahedral coordination of the metal centre. Whilst the material containing the discrete tetrameric anions (1 ) exhibits Curie-Weiss paramagnetism, (2 ) exhibits a spontaneous magnetization below Tc ≈ 14 K. The low saturation moment of ca. 0.02μB per cation, suggests that this involves a transition to a spin-canted state. More complex magnetic behaviour is observed in [enH2][Co3(SO4)3(OH)2] (5 ), the structure of which consists of layers of CoO6 octahedra that share edges to produce triangular units. Individual triangles of nine octahedra share common vertices to generate anionic layers. The layers have the topology of the kagome lattice but in contrast to the intensively studied jarosites, in which octahedra are vertex linked, (5 ) contains edge-sharing octahedra. Magnetic susceptibility data show a marked dependence on field, a divergence between field-cooled and zero-field-cooled data at 10K and |θ|/Tc = 6, indicative of a degree of magnetic frustration.


11:30 AM PP4.9
Switching-on (and off) Long Range Magnetic Order in LaCoO3: a First-principles Study of Spin-state Transitions. James M Rondinelli and Nicola A Spaldin; Materials, UC Santa Barbara, Santa Barbara, California.

We examine the perovskite compound LaCoO3, which has for more than 50 years, plagued both physicists and chemists alike, who have tried to understand the magnetic spin-state transitions that occur as a function of temperature, pressure and chemical doping. Much of the interesting physics in this cobaltite relies on the fact that d6 Co3+ cations, may be found in a non-magnetic low spin (S=0) ground state that can be excited to a magnetic, intermediate- (S=1) or high (S=2) spin-state, depending on local coordination environment. This apparent violation of Hund’s first rule and the observation of magnetic ordering in experiments have lead to an increased controversy over the true character of the Co3+ spin state. In this work, we use use first-principles density functional theory calculations to explain the spin-state transitions in three structural variants of LaCoO3. In order to accurately describe the material properties, we use an extension of the conventional local spin density approximation (LSDA) to include correlation with an on-site Hubbard U term (LSDA+U) to describe the electron-electron interactions for the Co 3d orbitals. We determine for the first time the critical value for U in this system, and show the sensitivity of electron-electron interactions, which influence the magnetic order, on the crystal structure. Since the valence bandwidth is strongly dependent on the oxygen octahedral tiltings and rotations in perovskite compounds, we show that with small perturbations of these parameters, control of metal-insulator transitions, concomitant with the onset of magnetic ordering, is possible. We conclude by outlining structural trends and properties in LaCoO3 that are accessible in the laboratory with chemical pressure (in bulk systems), or small strains (in thin films), and suggest this is a promising route for engineering switchable (on/off) magnetism.


11:45 AM PP4.10
Monitoring the Magnetic Properties of Novel Co/Fe Oxyhalides by Changing the Assembly Between Elementary Blocks. Olivier Mentre1, Sylvie Daviero-Minaud1, Pascal Roussel1 and Olivier Toulemonde2; 1UCCS UMR CNRS 8181, Villeneuve d'Ascq cédex, France; 2ICMCB, Bordeaux, France.

Cobaltites have attracted considerable interest in the last decade because of spectacular properties similar to those of the manganites and cuprates. In that field, our investigation of the Ba-Co-X (X =O, F, Cl, Br) systems has led to a number of new mixed-valent CoII/CoIII or CoIII/CoIV materials that has turned out to display complex physical properties. From the structural point of view, most of the concerned compounds and their dimensionality can be deduced from each other by the reorganization of structural blocks isolated by anionic layers. We have investigated the particular dependence of their magnetic orderings on the connectivity between the blocks and empirical rules have been found. Our results are in good agreement with the main conservation of intra-block properties and the variable role of the inter-block connectivity on the local Co moments and on the sign and strength of the magnetic exchanges. For instance, the modification of the 2H-BaCo3 through the replacement of [BaO3] layers by a [BaOX] layer (X=O, F, Cl)leads to a series of original related hexagonal-perovskite like materials. Further disconnections of the frameworks can be obtained using [Ba2O2Br] double layers. The magnetic orderings deduced from both magnetic measurements and neutron data largely depend on the nature of the inter-block geometrical features. Here, we present new results about their crystallographic/magnetic/spectroscopic specificities with respect to the relationship between the compounds. In addition, the partial substitution of Co for Fe in these oxyhalides leads to the CoIV-tetra/ FeIII-octa segregation. It yields ideal compounds for the spectroscopic investigation of the tetrahedral cobalt species, so far assigned to intermediate CoIV. In addition a new BaFeO3-x polymorph will be presented.


 

SESSION PP5/S6: Joint Session: Solid State Ionics for Energy
Chairs: Miguel Alario-Franco and Silvia Licoccia
Tuesday Afternoon, December 2, 2008
Back Bay C (Sheraton)


1:30 PM *PP5.1/S6.1
Lithium Metal Phosphates for Energy Storage. Linda Nazar, Brian Ellis, Jack Kan and Shriprakesh B Badi; University of Waterloo, Waterloo, Ontario, Canada.

Nanomaterials have the potential to significantly change the capacity and power delivery of energy storage systems. Amongst the most promising devices are Li-ion rechargeable batteries, where next-generation electrode materials could enable their implementation in hybrid electric vehicles and as reservoirs for intermittent energy sources such as solar energy, in order to address growing environmental concerns. Nanosized olivine LiFePO4 for example, amongst other lithium metal phosphates, has attracted much attention as a potential candidate for this aim. While conventional factors such as reduced path length for transport could also be at heart, claims have been made that in nanocrystallites of LiFePO4, reduced strain energy between the end members of the redox couple and/or increased solid solution regimes may be responsible for their enhanced electrochemical performance. Little unequivocal quantification of “nano” effects has been provided, however, owing to the difficulty of measuring them. This presentation will discuss these factors in a range of lithium metal phosphate nanocrystallites, including LiMPO4 (M = Fe, Mn); Na2FePO4F; Li2FePO4F; and some of their “doped” analogues. A broad range of techniques, including x-ray/neutron diffraction, conductivity, TEM/HREELS and Mössbauer measurements are used to probe differences in the temperature for the transition to the solid solution regime; the activation energy for small polaron hopping; and the stability of Li vacancies in bulk vs nanocrystallite materials.


2:00 PM PP5.2/S6.2
First-principles Studies of Phase Stability of LiFePO4 in Aqueous Solutions. Gerbrand Ceder, Lei Wang and Kristin Persson; Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts.

Olivine structure LiFePO4 has emerged as a promising high-rate cathode material in Li-ion batteries. In recent years much research effect has been devoted to the synthesis of this material in low temperature solution environments.[1, 2] The searching for optimum aqueous solution conditions where the precipitation of LiFePO4 is thermodynamically favored over other competing products is of great interest to the practical synthesis. Meanwhile, the effort of controlling the particle morphology for LiFePO4 in solution environment [3] is also important because the lithium diffusion for this material is believed to be one-dimensional in the olivine structure. We have developed a thermodynamic formalism to study the stability of metals and oxides in aqueous solutions. In this work, we demonstrate the methodology in LiFePO4 and investigate the thermodynamic equilibria between solid phases and aqueous ions in solutions. The stability of bulk LiFePO4 in aqueous solution is presented in the calculated Pourbaix diagram, which shows the phase equilibria as a function of potential and pH value of the solution. Previously, we studied the equilibrium particle morphology of LiFePO4 using the calculated surface energies for clean surfaces.[4] In this work, we consider the appearance of different adsorbates, e.g. H, OH, H2O, on the surfaces of LiFePO4 and investigate the change of surface energies and equilibrium particle shape in different solution conditions. By taking into account the surface absorption reactions, we are able to study the stability of LiFePO4 surfaces in aqueous solutions. And the corresponding modification of equilibrium morphology will be discussed in the calculated Pourbaix diagram for finite-size LiFePO4. Our results provide useful insights into the synthesis of LiFePO4 in solution environments and the change of particle morphology in different solution conditions. Reference: [1] J. J. Chen and M. S. Whittingham, Electrochem. Commun. 8, 855 (2006). [2] C. Delacourt, P. Poizot, S. Levasseur, and C. Masquelier, Electrochemical and Solid State Letters 9, A352 (2006). [3] K. Dokko, S. Koizumi, and K. Kanamura, Chemistry Letters 35, 338 (2006). [4] L. Wang, F. Zhou, Y. S. Meng, and G. Ceder, Phys. Rev. B 76, 165435 (2007).


2:15 PM PP5.3/S6.3
Ion-Exchange and Subsequent Li-Insertion Chemistry of a New Family of Iron Phosphate Compounds Exhibiting Channeled Structures. Gregory A Becht1, John T Vaughey2, Robin L Britt3, Cassandra T Eagle3 and Shiou-Jyh Hwu1; 1Department of Chemistry, Clemson University, Clemson, South Carolina; 2Chemical Sciences and Engineering, Argonne National Laboratory, Argonne, Illinois; 3Department of Chemistry, Appalachian State University, Boone, North Carolina.

Since the demonstration of the reversible extraction of lithium from LiFePO4 (triphylite), an enormous amount of effort has been devoted to the identification of other lithium insertion compounds that can be used as cathodes for secondary lithium battery devices. Among iron-containing polyanion-based compounds include the NASICON-type Li3Fe2(PO4)3 as well as pyrophosphates LiFeP2O7 and Fe4(P2O7)3. While the olivine-type LiFePO4 has maintained prominence, it has some inherent shortcomings, including one-dimensional Li+-ion transport and a two phase redox reaction. Thus, electrochemical extraction was reportedly limited to ca. 0.6 Li/formula unit, which is equivalent to the specific capacity of 100-110 mAh/g. The discovery of new open-framework solids that technically exhibit pathways for facile Li+ transport, extended charge/discharge capacity, and structure stability upon electrochemical cycling is especially critical for the development of large-capacity systems required in technologies such as plug-in hybrid electric vehicles. A newly devised synthetic approach, combining high-temperature solid-state and low- temperature solution methods, has allowed the discovery of new lithium iron phosphate compounds that otherwise cannot be synthesized directly through conventional solid-state methods. By employing molten salt methods, we have isolated several new iron phosphate compounds containing large alkali metal cations in layered and channeled structures. These new solids were subject to ion-exchange and reduction insertion with Li+ cations. The parent structure used in the ion-exchange reported here was Cs9-xKxFe7(PO4)10. The electropositive cations, Cs+ and K+, reside in two interconnected orthogonal channels. Consequently, the direct ion exchange on single crystals was proven possible under mild hydrothermal conditions in 1M nitrate solutions, and it has revealed remarkable ion exchange properties with all of the monovalent alkali metal cations. Employing a n-BuLi/hexane solution, the ion-exchanged Fe(III) compound Li9Fe7(PO4)10 can be further lithiated to a reduced Fe(II) phosphate phase Li16Fe7(PO4)10 at room temperature. In this presentation, we will discuss the synthesis, structure and electrochemical properties of these newly synthesized iron phosphate compounds. We will also discuss the use of large electropositive cations as a template for the synthesis of new open-framework compounds and offer insight into the synthesis of new Fe(III)-containing phosphate compounds having structural versatility and extended capacity.


2:30 PM *PP5.4/S6.4
New Mechanisms of Li Insertion/extraction in LiFePO4. Christian Masquelier1, Pierre Gibot1, Montse Casas Cabanas1, Lydia Laffont-Dantras1, Stéphane Levasseur2, Philippe Carlach2, Stéphane Hamelet1 and Jean-Marie Tarascon1; 1LRCS, Chemistry Dept., Université Picardie Jules Verne, Amiens, France; 2UMICORE Research, Olen, Belgium.

LiFePO4 is now recognized (and used) as a new electrode material for Li-ion batteries as it represents a low cost and non toxic material that exhibits high specific capacity and stability upon cycling. Li ions can be reversibly removed from the structure, leading to the formation of FePO4 in a two-phase process with a theoretical specific capacity of 170 mAhg-1 [1]. Its main drawback is its low electrical conductivity and effective approaches such as the use of LiFePO4/carbon composites [2-3] or the minimization of particle sizes [4] have been proposed to overcome this limitation. Downsizing LiFePO4 particles to the nanometric scale indeed translates in an improved electrochemical activity against lithium as the electrode/electrolyte contact area is increased, which yields higher cycling rates, and the mean path lengths for both electrons and lithium cations are minimized, allowing the use of low electronic and/or ionic conducting materials. The crystal chemistry and electrochemical behavior of various nanometric “LiFePO4” powders prepared by direct precipitation in water [5] will be presented. We report on the discovery, probed by insitu X-Ray diffraction, of a full solid solution process during Li+ extraction / insertion at room temperature for triphylite nanopowders that contain significant amounts of defects on the Li and Fe octahedral crystallographic sites, as deduced from Rietveld analysis of powder neutron diffraction data [6]. The possibility of having single phase extraction/insertion mechanisms (e.g., a sloping voltage curve) presents some intrinsic advantages with respect to applications such as an easier and cheaper monitoring state of charge of the battery as compared to a flat constant voltage curve. References [1]. A.K. Padhi, K.S. Nanjundaswamy, J.B. Goodenough, J. Electrochem. Soc., 144(4) 1188-1194 (1997). [2]. H. Huang, S.C. Yin, L.F. Nazar, Electrochem. Solid-State Lett., 4(10), A170-A172 (2001). [3]. N. Ravet, J.B. Goodenough, S. Besner, M. Simoneau, P. Hovington, M. Armand, Abstract #127, 196th ECS meeting, Honolulu, 17-22 October 1999. [4]. C. Delacourt, P. Poizot, S. Levasseur, C. Masquelier, Electrochem. Solid-State Lett., 9(7), A352-A355 (2006). [5] Delacourt, C., Poizot, P., Masquelier, C., Crystalline nanometric LiFePO4, World Patent, CNRS-UMICORE, #WO 2007/0051 (2007) [6]. P. Gibot, M. Casas-Cabanas, L. Laffont, S. Levasseur, P. Carlach, S. Hamelet, J.M., C. Masquelier, Nature Materials, in press, (2008)


3:30 PM *PP5.5/S6.5
Designing The Next Generation of Proton Conductors. Sossina M Haile1, Calum R Chisholm1,2 and Eric Toberer1; 1Materials Science / Chemical Engineering, California Institute of Technology, Pasadena, California; 2Superprotonic, Inc., Pasadena, California.

Solid acids, or acid salts, are a class of proton conducting electrolytes with stoichiometries MHXO4, M3H(XO4)2 (M = Cs, Rb, NH4; X = S, Se), and MH2X’O4 (X’ = P, As). Many of these compounds undergo a remarkable phase transition at which the proton conductivity jumps by three to four orders of magnitude to a “superprotonic” state with conductivity in the range of 10-3-10-1 Ω-1 cm-1. These high levels of conductivity are a result of rapid librations of the tetrahedral oxyanion groups ( ~ 1012 Hz) in combination with a high rate of proton transfer between tetrahedral groups (~ 109 Hz). A curious feature of these materials is the apparent restriction of superprotonic behavior to compounds in which the M cation is either an alkali metal or the ammonia ion. In this work we explore the possibility of extending superprotonic solid acids to compounds based on alkaline earth metals, with particular emphasis on derivatives of Ba3(PO3)2. Through a combination of X-ray powder diffraction, 1H NMR spectroscopy, thermal gravimetric analysis, energy dispersive chemical analysis, and conductivity measurements, we show that it is possible to partially substitute K + H for Ba, and create crystal-chemical analogs to the known superprotonic conductors MH3(SeO4)2. While the conductivities of the alkaline earth phosphate materials are lower than those of the alkali selenates, this new class of proton conductors displays key advantages for practical applications, including chemical stability in reducing atmospheres and insolubility in water.


4:00 PM *PP5.6/S6.6
Composite Effects of Pyrophosphate Matrices on the Proton Conductivity for CsH5(PO4)2 Electrolytes at Intermediate Temperatures. Toshiaki Matsui, Hiroki Muroyama, Ryuji Kikuchi and Koichi Eguchi; Department of Energy & Hydrocarbon Chemistry, Graduate school of Engineering, Kyoto University, Kyoto, Japan.

Solid state fuel cells operative at 200-300oC, so-called intermediate-temperature fuel cells, are one of the promising technologies since they combine many advantages of low- and high-temperature fuel cells, i.e., suppression of the CO poisoning of Pt catalyst, enhancement of the energy conversion efficiency, and use of metallic and plastic components. Recently, at intermediate temperatures, some oxo-acid salts and their composites have been attracted attention as proton-conductive electrolytes. The electrolyte of CsH2PO4/SiP2O7-based composite was reported to exhibit an anomalous phenomenon with high conductivity. In this composite, CsH5(PO4)2, which was formed by the reaction of the part of CsH2PO4 and SiP2O7, served as a new proton-conductive phase. Then, to elucidate the proton-conduction mechanism in this composite, CsH5(PO4)2 composites have been studied. The SiP2O7 and hydrophilic-SiO2 were selected as matrices. The CsH5(PO4)2/SiP2O7 composite showed much higher conductivity than CsH5(PO4)2/hydrophilic-SiO2 composite in spite of the relatively high molar concentration of CsH5(PO4)2. Therefore, this indicated the matrices should play an important role in the proton-conduction mechanism. In this study, CsH5(PO4)2 composites were synthesized by using various matrices, and their influence on the proton-conductivity was investigated at intermediate temperatures. Temperature dependences of the conductivity for CsH5(PO4)2 composites under 30% H2O/Ar atmosphere was investigated. Below 150oC, the conductivity of the all composites increased drastically with temperature because of the melting of CsH5(PO4)2. Above 150oC, CsH5(PO4)2/SiP2O7 and CsH5(PO4)2/SiO2 composites exhibited higher conducitivity with a value of 50 mS cm-1 at 230oC. The molar content of CsH5(PO4)2 in every CsH5(PO4)2/MP2O7 composite (M = Si, Ti, and Zr) was almost the same, while that in CsH5(PO4)2/SiO2 composite was higher by 1.5 times than the others. Consequently, these results indicated that the matrix of SiP2O7 exhibited the best compatibility with CsH5(PO4)2 in all composites investigated, and the interfacial interaction between CsH5(PO4)2 and the marix significantly depended on the metal speices of pyrophosphates.


4:30 PM *PP5.7/S6.7
Ionic Conduction in the Solid-state, the Influence of Defect-defect Interactions. Paul Madden and Dario Marrocchelli; School of Chemistry, University of Edinburgh, Edinburgh, United Kingdom.

At the simplest level, ionic conduction in the crystalline state is due to the hopping of vacancies and interstitials. However, when such defects are introduced by aliovalent doping the ionic conductivity often does not increase with the defect concentration, as might be expected from this simple picture. A good example is the case of yttria-stabilized zirconia, which is often used as an oxide ion conductor in solid-oxide fuel cells. Here, the conductivity decreases with increasing yttria content for doping levels beyond about 10%. Several factors could contribute to this effect - trapping of vacancies by spatial fluctuations in the dopant cation concentration, interactions between the vacancies causing the formation of low mobility clusters…….To distinguish between these effects by purely experimental means is very difficult, the interactions may have weak consequences in diffraction or thermochemistry but even if such structural effects are detected there is no direct way of linking them to the conduction mechanism. Here we describe computer simulation studies on transition metal oxide mixtures carried out with polarisable interaction potentials parameterized from ab initio electronic structure calculations. The calculations reproduce extremely well the experimental data for the conductivity and also the structural information obtained by analysis of the total (Bragg and diffuse) neutron scattering. By introducing a third cation, such as Nb5+ and varying the composition, such experiments have been performed on a range of samples with the same vacancy concentration, which enables the different influences on the conductivity to be traced. The simulations may be interrogated at the atomic level to clarify the important influences on the ionic conduction mechanism.


 

SESSION PP6: Synthesis, Properties, and Characterization of Nanomaterials
Chairs: Paul O'Brien and Wolfgang Tremel
Wednesday Morning, December 3, 2008
Back Bay C (Sheraton)


8:30 AM *PP6.1
Wet Chemical Synthesis of Gold and Silver Nanowires. Catherine Jones Murphy, Dept of Chemistry, University of South Carolina, Columbia, South Carolina.

Previously in our laboratory, we have developed a surfactant-directed, seed-mediated growth approach to synthesize gold and silver nanorods of controllable aspect ratio. More recently, in contrast, we have developed a wet chemical method to make long silver nanowires in solution that requires no external seed nor any surfactant. Preliminary data suggest that an oriented attachment mechanism may be operative. The physical properties and chemical reactivity of these silver nanowires (including a reaction to make long gold nanotubes) will be discussed.


9:00 AM PP6.2
Investigation of Zeolites as Templates for the Formation of Transition Metal Nanowires. Maria Martinez-Inesta, University of Puerto Rico, Mayaguez, Puerto Rico.

The use of templates has demonstrated to be a cost effective reliable method for the formation of uniform structures. Membranes of macropore (larger than 50 nm) and mesopore (between 2 and 50 nm) dimensions have been successfully used for the formation of metallic nanowires. However there is little evidence in the literature of studies using templates of micropore dimensions for the formation of nanowires. Here we will present work done using zeolites as templates for the formation of transition metal nanowires. Zeolites are crystalline aluminosilicate materials that possess 1D, 2D and 3D pore structures that range in sizes from 0.4 nm to 1.3 nm, thus its use as templates have the potential of yielding the smallest uniform nanostructures available through a bottom up method. Our group has studied this system using both computational and experimental methods. Computationally the effect of zeolite structure, zeolite composition, and metal loading on the formation of nanowires has been studied using Monte Carlo simulations and we have identified zeolites with optimal structures for the growth of nanowires. Experimentally we have used zeolite mordenite and VPI-8, both zeolites with a unidimensional pore structure, as templates to study the formation of Pt nanowires. The effect of the Pt incorporation method, the role of an oxidation step, and various reduction methods has been studied and the materials have been characterized during the synthesis by XRD, N2 physisorption, H2 chemisorption, and HRTEM. Thus far our group has been successful synthesizing polycrystalline Pt nanowires of 2nm in diameter that are being tested for catalytic as well as sensor applications. Other nanostructures formed are nanoparticles and nanowires of larger diameters.


9:15 AM PP6.3
Direct Current Electro-deposition of Ternary Fe48Co36Ni16 Alloy Nanorod Arrays. Joseph F. Chiang1, Shouhong Xue2, Chanbao Cao3, Mei Li2 and Ximin Xu2; 1Chemistry and Biochemistry, SUNY-Oneonta, Oneonta, New York; 2Inner Mongolia University of Science and Technology, Baotou, China; 3Beijing Institute of Technology, Beijing, China.

Highly ordered arrays of ternary Fe48Co36Ni16 alloy nanorods with cylindrical morphology have been successfully prepared by direct current electro-deposition using polycarbonate (PC) membrane template. The two ends of nanorod arrays have diameters of 200 and 320 nm, respectively. The nanorod arrays can be as long as 7~8 μm. The Fe/Co ratio in the ternary FeCoNi alloy nanorod arrays was equal to the Fe2+/Co2+ ratio in electrolyte that revealed the variable Fe/Co ratio of ternary FeCoNi alloy nanorod could be controlled by adjusting the Fe2+/Co2+ ratio in electrolyte. The coercivities of as-prepared Fe48Co36Ni16 nanorod arrays for the applied field parallel and perpendicular to the nanorods are about 2500 and 138Oe, respectively, which were much higher than that of their bulk and film materials. The large parallel coercivity (2500 Oe) and high squareness (Mr/Ms) (about 0.75) are very important to the magnetic head materials. Key words: Nanostructured materials; Chemical synthesis; Magnetic measurements


9:30 AM PP6.4
Synthesis and Morphology Control of the FeCo Nanoparticles. Girija S Chaubey, Narayan Poudyal, Chuanbing Rong and J Ping Liu; Physics, University of Texas at Arlington, Arlington, Texas.

FeCo alloys are an important soft magnetic material because of their unique magnetic properties including large permeability and very high saturation magnetization. FeCo nanoparticles have attracted great interests recently because of their applications as building blocks of advanced nanomagnets and applications in biomedical technologies. We report a novel method for the synthesis of monodisperse FeCo nanoparticles with controllable particle size and size distribution. The synthesis procedure is based on reductive decomposition of organometallic precursors in presence of surfactants. Nanoparticle size between 9 to 20 nm was tuned by varying the reaction parameters. FeCo nanowire was also obtained by varying the reaction conditions such as heating rate and refluxing time. The saturation magnetization values of the as-synthesized nanoparticles are found to vary with composition and size of the nanoparticles. Large particles have higher magnetization. The highest magnetization of 206 emu/g has been obtained for 20 nm particles. In addition, we also worked to stabilize the nanoparticles in ambient condition and have found that the as-synthesized FeCo nanoparticles become air-stable after annealing at 500 oC for 30 min.


9:45 AM PP6.5
Control of Phase in Discrete (Unsupported) Nanoparticles of MnAs: Consequences for the First Order Magnetostructural Transition. Keerthi Senevirathne1, Ronald J Tackett2, Parashu Ram Kharel2, Gavin Lawes2 and Stephanie L Brock1; 1Chemistry, Wayne State University, Detroit, Michigan; 2Physics and Astronomy, Wayne State University, Detroit, Michigan.

Bulk MnAs exhibits a characteristic first order magnetostructural phase transition from the ferromagnetic NiAs structure (α-type) to the paramagnetic MnP structure (β-type) at 317 K. Associated with this transition are large magnetocaloric, magnetooptical, and magnetoresistive effects, which makes this material of interest for applications ranging from magnetic refrigeration to data storage. Recently, nanoparticles of MnAs have been reported by epitaxial growth on GaAs or InAs substrates. The resultant nanoparticles are subjected to epitaxial strain, which shifts the magnetostructural transition temperature, TC, to higher temperatures, and even enables a co-existence of the two phases near TC. In this presentation, a solution-phase synthesis of discrete, unsupported MnAs nanoparticles in the size range 8-30 nm is reported. Depending on the synthesis conditions, either the α or β phase can be stabilized at room temperature. Intriguingly, the β-phase begins to transform to the thermodynamically stable α-phase only after several weeks at room temperature, and routine heating of the α-phase samples to temperatures approaching 400 K does not result in the expected transformation to the β phase. Despite the structural differences and the slow kinetics of the phase transformation, nearly identical magnetic behavior, including the ferromagnetic-to-paramagnetic transition at 317 K, are observed in both α and β samples. The effect of nanoparticle isolation on the facility for nucleation of first order transitions, and the relationship between this structural transition and the magnetic transition, will be discussed.


10:30 AM *PP6.6
Electrochemical Morphology Control of Inorganic Electrodes. Kyoung-Shin Choi, Chemistry, Purdue University, West Lafayette, Indiana.

Most modern electrochemical and photoelectrochemical devices require semiconducting or metallic electrodes and catalysts as the main components. When the electrodes are processed as polycrystalline films, particle shapes, sizes, orientations, and interconnections significantly affect the chemical and physical factors that define the energetics and kinetics of these electrodes. Therefore, rationally controlling micro- and nano-scale structures of inorganic materials that compose polycrystalline electrodes, and understanding the effects micro- and nano-structures have on functional properties are essential to produce high performance and cost effective electrode materials. To achieve these goals, we have been developing new synthetic strategies by combining the compositionally versatile electrodeposition methods with various synthetic concepts that can precisely regulate morphological features of inorganic materials at various length scales. In this presentation, we will discuss in detail how intrinsic advantages of electrochemistry can be exploited to manipulate basic growth processes of inorganic materials in a systematic manner. Various strategies to methodically control crystal shapes, dendritic growth, and fibrous growth during electrochemically preparing metallic and semiconducting electrodes (e.g. Zn, Sn, Cu2O ZnO, SnO2) will be presented. The effect of these morphologies on electrochemical and photoelectrochemical properties will be discussed in order to identify optimum morphologies to enhance desired properties.


11:00 AM PP6.7
Precursor Decomposition Approach for the Synthesis of Metals, Oxides, Sulfides and Carbides for Various Applications. Vilas Pol1 and M. Thackeray2; 1Argonne National Laboratory, Argonne, Illinois; 2CSE, Argonne National lab, Argonne, Illinois.

This seminar focused on the synthesis of variety of nanomaterials using novel RAPET (Reactions under Autogenic Pressure at Elevated Temperature) technique, characterization and study of their fascinating properties. The RAPET approach is suitable for the synthesis of superconducting, semiconducting and magnetic nanomaterials. Unique properties, such as high intra-grain critical current density in MgB2 nanocrystals, 2.5 wt. % hydrogen storage in SiC nanorods, suppressed phase transformation in TiO2 with enhanced photocatalytic activities, novel luminescence from ZnO micro / nanopencils, stabilization of metastable tetragonal phase of ZrO2 with in-situ formed carbon shell and 10% negative magnetoresistance in fullerene like Ni-C core-shell nanostructure, will be presented. The effect of an external magnetic field of 10 Tesla on the fabrication of magnetically susceptible materials will be demonstrated. The testing of novel V2O5-C core-shell nanostructure as a cathode material for Li ion batteries, which achieves reversible capacities close to theoretical value will be shown. References 1. Pol, S. V. ; Pol, V. G.; Gedanken, A. Adv. Mater. 2006, 18, 2023. 2. Odoni, A.; Pol, V. G.; Pol, S. V.; Aurbach, D.; Gedanken, A. Adv. Mater. 2006, 18, 1431. 3. Rana, R. K.; Pol, V. G.; Felner, I.; Meridor, E.; Frydman, A.; Gedanken, A. Adv. Mater. 2004, 16, 12. 4. Pol, V.G.; Pol, S. V.; Gedanken, A.; Lim, S. H.; Zhong, Z.; Lin, J. J. Phys. Chem.B, 2006, 110, 11237. 5. Pol, V. G.; Pol, S. V.; Felner, I.; Gedanken, A. Chem. Phys. Lett. 2006, 433, 115. 6. Pol, S. V.; Pol, V. G.; Seisenbaeva, G.; Kessler, V. G.; Gedanken, A.Chem. Mater. 2004, 16, 1793.


11:15 AM PP6.8
Porous Oxide Shell through Surface-Protected Etching. Yadong Yin, Qiao Zhang, Jianping Ge, Yongxing Hu and Tierui Zhang; Chemistry, University of California, Riverside, California.

We describe a “surface-protected etching” strategy that allows convenient conversion of sol-gel derived colloidal oxides into porous shell structures. A polymeric ligand is used to protect the surface layer and an appropriate etchant is used to selectively etch the interior of the oxide materials such as sol-gel derived colloids. Etching initially yields porous structures, and eventually removes the core to leave behind hollow spheres with porous shells. We have been able to demonstrate the concept for colloidal particles including titanium oxide and silicon dioxide. This strategy is useful for constructing core-shell systems where active nanomaterials are embedded in oxide shell for enhanced stability against aggregation. We experimentally demonstrate use of the surface protected etching approach to create openings on silica shells; these openings allow dissolved chemical species to reach embedded catalytic particles to be chemically transformed while the porous shells continue to act as effective barriers against aggregation and loss of activity of the core particles. We also show that by controlling the extent of etching, it is possible to control the permeation rate of the chemical species through the shells.


11:30 AM PP6.9
Redox Induced Adsorption Geometry Change of Supported Metal-oxide Catalysts. Chang-Yong Kim1, Zhenxing Feng2, Jeffrey W Klug2, Steve T Christensen2, Jeffrey W Elam3, Joseph A Libera3, Peter C Stair4,3 and Michael J Bedzyk2; 1Canadian Light Source, Saskatoon, Saskatchewan, Canada; 2Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois; 3Chemistry Division, Argonne National Laboratory, Argonne, Illinois; 4Department of Chemistry, Northwestern University, Evanston, Illinois.

Supported metal oxides are among the most important of catalytic materials systems. However, there is a lack of experimental atomic-scale structural information for describing the relevant interfaces. By using x-ray photoemission spectroscopy (XPS) and x-ray standing wave (XSW) measurements, adsorption geometries of vanadium oxides in oxidize and reduced phases have been studied. The V adlayers were prepared on alpha-Fe2O3(0001) and rutile TiO2(110) surfaces by the MBE and atomic layer deposition (ALD) methods. The oxidation state of the V was measured with the XPS. The XSW analysis results are used to generate a direct-space, model-independent image of the V distribution. [1,2] In conjunction with XPS results, the direct-space atomic density profiles reveal that the V occupies high-symmetry surface sites except V5+ on rutile TiO2(110), and the oxidation state change induces redistribution of vanadium adatom. The vanadium adatoms in oxidized (V5+) and reduced (V3+) phases occupy bulk-like substitution sites on the alpha-Fe2O3(0001) surface. The occupation of bulk-like substitution sites has been observed also for the VOX deposited on TiO2(110) surface, but only in reduced phase (V4+). The oxidized V5+ does not occupy high-symmetry site but makes bonds with three lattice oxygen atoms of TiO2(110) surface to form a tetrahedron. Our current results suggest that geometries of the supported vanadium oxides are determined not only by oxidation state of the V but also by surface symmetry of substrate. 1. L. Cheng, P. Fenter, M. J. Bedzyk, and N. C. Sturchio, Phys. Rev. Lett. 90, 255503 (2003). 2. Z. Zhang, P. Fenter, L. Cheng, N. C. Sturchio, M. J. Bedzyk, M. L. Machesky, and D. J. Wesolowski, Surf. Sci. 554, L95 (2004).


11:45 AM PP6.10
In-situ Structural Studies of Heterogeneous Catalysts Using the Pair-Distribution-Function Method. Peter Chupas1, Karena W Chapman1, Guy Jennings1, Peter Lee1 and Clare Grey2; 1X-ray Science Division, Argonne National Laboratory, Argonne, Illinois; 2Department of Chemistry, Stony Brook University, Stony Brook, New York.

There is growing recognition in the catalysis community of the need to study materials under realistic reaction conditions, with both time resolution that matches the reaction rate, and with atomic resolution. Recent advances in PDF measurements combining 2-dimensional area detectors and high-energy X-rays have dramatically decreased measurement times for high resolution PDF (Pair-Distribution-Function) measurements to times as fast as 30 milliseconds. The PDF technique recovers structural information, in the form of a radial distribution of atom-atom distances without the assumptions of symmetry constraints that crystallographic approaches rely on. Information on both the local and intermediate range length scales is probed, and therefore PDF is an ideal match for studying catalysts. Specifically this talk will cover two areas; (1) Time-resolved PDF measurements investigating the mechanism and kinetics of formation of supported catalytic nano-particles, and (2) The use of the technique to probe the structure of reactive sites at surfaces. By applying the differential PDF approach, structural information regarding only active sites on surfaces can be recovered with unprecedented detail, bridging the pressure gap with ultra-high vacuum surface science techniques and thus allowing fundamental structural studies on real samples.


 

SESSION PP7: Nanostructures and Thin Films
Chairs: David Johnson and John Wiley
Wednesday Afternoon, December 3, 2008
Back Bay C (Sheraton)


1:30 PM *PP7.1
Synthetic Approaches to Functionalized Chalcogenide Nanotubes. Wolfgang Tremel1, Aswani Yella1, Helen Annal Therese1, Muhammad N Tahir1, Jugal Sahoo1, Martin Panthöfer1, Heinz-Christoph Schröder2 and Werner E Müller2; 1Institut für Anorganische Chemie und Analytische Chemie, Johannes Gutenberg-Universität, Mainz, Germany; 2Institut für Physiologische Chemie, Johannes Gutenberg-Universität, Mainz, Germany.

In addition to carbon nanotubes, non-carbon nanostructures have attracted much attention over the past few years. In particular, and due to their unusual geometry and promising physical properties, inorganic fullerene nanostructures have become one of the key topics in nanoscale research since the first report on WS2 nanotubes by Tenne and coworkers. Various synthesis techniques for the synthetis chalcogenide nanotubes have been established so far, the most successful one being oxide to sulfide conversion. We have devised new methods for the synthesis of chalcogenide nanotubes. One approach exploits recent developments in metal-catalyzed nanowire synthesis, which have shown that nearly monodisperse metal nanoclusters can be used to control the diameter and (through growth time) the length of semiconductor nanowires through a vapor-liquid-solid (VLS) growth process. We introduce the vapor phase required for nanotube growth by gentle heating of solid precursors, while an inert carrier gas provides the required dilution of the vapor-phase species. Metal droplets catalyze the formation of SnS2 nanotubes by providing a nucleation surface. Chalcogenide nanotubes are attractive building blocks for a hierarchical assembly of functional nanoscale devices that eventually could overcome limitations of conventional lithographic fabrication. We have devised new functionalization protocols for chalcogenide nanoparticles. As an example we demonstrate the covalent bio-functionalization of WS2 nanoparticles and their subsequent coating with biotitania.


2:00 PM PP7.2
Bio-Hybrid Elastomers by Assembling of Vanadium Oxide and Gelatin. Florent Carn1, Madeleine Djabourov2, Bruno Fayolle3, Olivier Durupthy1, Thibaud Coradin1, Jacques Livage1 and Nathalie Steunou1; 1Chimie de la Matière Condensée de Paris, UPMC, Univ Paris 06, Collège de France, Paris, France; 2Laboratoire de Physique Thermique, ESPCI, Paris, France; 3Laboratoire d’Ingénierie des Matériaux, ENSAM, Paris, France.

Bionanocomposites represent an emerging group of nanostructured hybrid materials formed by the combination at the nanometer scale of natural polymers and inorganic solids. Similarly to classical nanocomposites that involve synthetic polymers, these bio-hybrid materials exhibit improved structural and functional properties (mechanical properties, high thermal stability and gas-barrier properties). In addition to these characteristics, the properties inherent to the biopolymers such as biocompatibility and biodegradability as well as those arising from the synergistic assembling of biopolymers with inorganic phases has led to the development of multifunctional materials with a wide number of potential applications. Since most of the bionanocomposites prepared so far are made of biogenic or biocompatible inorganic phases such as silica, hydroxyapatite and clay minerals, the application fields of regenerative medicine, green chemistry, food packaging are mainly concerned.1 In contrast, a few transition metal oxides were recently associated to biopolymers to design electrochemical, optical, and photochromic devices. This communication deals with the bio-inspired synthesis of vanadium oxide-gelatin hybrids that exhibit interesting viscoelastic properties. Vanadium oxide is of peculiar interest mainly due to its wide range of potential applications from catalysis, photochromism and positive electrode materials for Li-batteries. Gelatin is a protein that is able to form, transparent, elastic and thermoreversible gels that are suitable for the homogeneous dispersion of inorganic particles. A new type of hybrid elastomer based on electrostatic interactions between the decavanadate polyanions and gelatin was isolated. The material structure and morphology has been fully characterized by 51V MAS NMR, XRD, SEM and TEM whereas its mechanical behavior has been quantified under tensile load. The mechanical properties of this elastomer in comparison with those of gelatin were significantly improved, showing that the decavanadate polyanion can act as a reinforcing agent of gelatin. In aging conditions, we have observed by XRD and TEM investigations that the interactions between decavanadate and gelatin at the organic-inorganic interface strongly affect the V2O5 network growth by slowing down the condensation process and preventing the regular layers stacking in the material. This work has clearly shown that the formation mechanism of this elastomer could be described by a coacervation process, mainly reported for the interactions between biologic and/or organic macromolecules.2 Furthermore for dilute solutions, the influence of decavanadate on the nucleation of gelatin triple helices was studied by combining rheological and thermodynamic measurements. [1] M. Darder, P. Aranda, E. Ruiz-Hitzky, Advanced Materials, 19 (2007) 1309-1319. [2] F. Carn, N. Steunou, M. Djabourov, T. Coradin, F. Ribot, J. Livage, Soft Matter, 4 (2008) 735-738.


2:15 PM PP7.3
Polymer Nanocomposite Dielectric Materials for the Preparation of High Energy-Density Capacitors. Hans-Conrad zur Loye1, Harry J Ploehn2 and Peter Barber1; 1Chemistry & Biochemistry, University of South Carolina, Columbia, South Carolina; 2Chemical Engineering, University of South Carolina, Columbia, South Carolina.

Existing dielectric capacitors have quite low energy densities, both on a volume and mass basis. Electrochemical capacitors, including double layer capacitors and supercapacitors, offer high energy and power density, but their rate capability is limited by mass transfer and faradaic reaction rates - a critical issue for delivering pulsed power. To develop materials that combine high breakdown voltage and high dielectric constants, we are working on the development of new polymer nanocomposite dielectric materials. To achieve these goals, we are incorporating high dielectric constant inorganic platelet materials into polystyrene, where the uniform dispersion of the platelet material into the polymer is important and typically requires the functionalization of the platelet surface with organic groups. In this talk, the synthesis of new mixed-metal phosphonate materials and their use in the preparation of polystyrene based polymer nanocomposite dielectric materials will be discussed.


2:30 PM PP7.4
VO2 and V2O3 Nanostructures: Crystal Structure, Morphology and Electrical Properties. Serena A Corr and Ram Seshadri; Materials Research Laboratory, University of California, Santa Barbara, California.

Vanadium oxide materials have received considerable attention not only for their potential uses in a number of technological applications, but also because of the interesting physics associated with the metal to insulator transitions displayed by a number of these oxides. We have used several synthetic routes for the preparation of vanadium oxide nanostructures and have studied the structure, morphology and electrical properties of these materials. Firstly, we have carried out a systematic study of the reduction of vanadium oxide nanoscrolls for the large-scale preparation of nanostructures of rutile VO2 and corundum V2O3. The scrolls have been prepared by the hydrothermal treatment of V2O5 and dodecylamine and were subsequently reduced in a furnace in 5%H2:95%N2 under varying time and temperature conditions to form nanotubes. Use of a systematic study has allowed us to monitor the transformation from rutile VO2 at lower temperatures and shorter reduction times to corundum V2O3 at higher temperatures and longer reduction times. Along with measuring the electrical properties of these nanostructures, the structural transformation from monoclinic to tetragonal rutile VO2 has been studied using in situ thermodiffractometry. Interestingly, the appearance of the corundum V2O3 phase in x-ray diffraction is accompanied by an increase of nanocrystalline material on the surface of the nanotubes, as noted from electron microscopy. In another study, we have prepared in a single solvothermal step the metastable VO2(B) phase as a precursor to rutile VO2 and corundum V2O3 using several reducing agents. Electrical property characterization, in conjunction with thermodiffractometry experiments and magnetic measurements, have allowed us to probe the metal-insulator transitions in these materials.


2:45 PM PP7.5
Synthesis and Mechanical Behavior of Nanoporous Pt. Antonia Antoniou2, Dhriti Bhattacharyya1, Nathan Mara3, S. Tom Picraux1 and Amit Misra1; 1Center for Integrated Nanotechnologies, Los Alamos National Lab, Los Alamos, New Mexico; 2Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia; 3MST-6, Los Alamos National Lab, Los Alamos, New Mexico.

We have synthesized nanoporous Pt films on a silicon substrate by electrochemical dealloying. Amorphous PtxSi1-x films were co-sputtered and silicon was selectively dissolved in an aqueous HF solution. The remaining platinum was self assembled in a three dimensional network of nano-sized ligaments and pores. Ligament and pore sizes were investigated by varying a) the Pt to Si ratio in the amorphous films, b) the co-sputtering conditions and c) the electrochemical dealloying conditions. For the different conditions studied, ligament and pore sizes varied from 15-30nm while grain sizes within ligaments were ~5-10nm. The mechanical properties of these films were investigated through nanoindentation and compression testing of focused-ion-beam (FIB) machined micro-pillars. The dependence of strength was studied as a function of nanofoam porosity as well as ligament size to understand length scale effects. We observe ultra-high strengths (~1GPa) in nanoporous platinum films that are not explained by the scaling laws for the strength of bulk metallic foams as a function of foam density. The mechanical behavior of nanoporous metallic films is discussed in terms of deformation mechanisms involving nucleation of plasticity events at free surfaces. This research is supported by DOE, Office of Science, Office of Basic Energy Sciences.


3:30 PM *PP7.6
Single Source Route for the Deposition of Metal Chalcogenide Materials. Paul O'Brien and Mohammad Azad Malik; Chemistry, The University of Manchester, Manchester, United Kingdom.

Stable metal chalcogenide complexes have been proven to be useful as single-molecule precursors for the deposition of metal chalcogenide thin films or nanoparticles. We have synthesised a series of dithio-or di-seleno-carbamato metal complexes [(M(E2CNR2)2], dithio- or diseleno-phophinato metal complexes [M(E2PR2)2]2, diimido-dithio- or diseleno-diphosphinatometal complexes [M((E2PR2)2N)2], and most recently tetramethyl-2-4-dithiobiuratometal complexes M(tmtb)2, or dialkyl-N-benzoylselenoureato metal species (M= Zn, Cd, Pb, In, or Ga; E = S or Se) . All of these complexes have been used for the deposition of metal chalcogenide thin films by CVD or the growth of nanoparticles by colloidal routes. Most of these complexes are crystalline solids and their structures have been determined by X-ray single crystallography. The as-obtained materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive X-ray analysis (EDAX). Significant aspects of the chemistry of the decomposition of precursors will be discussed. References: A. Panneerselvam, M. A. Malik, M. Afzaal, P. O’Brien and M. Helliwell, J. Am. Chem. Soc., 2008, 130, 2420; C. Q. Nguyen, M. Afzaal, M. A. Malik, P. O’Brien, M. Helliwell, and J. Raftery J. Organomet. Chem., 2007, 692, 2669; B. Ludolph, M.A. Malik, P.O’ Brien and N. Revaprasadu., J. Chem. Soc. Chem. Comm., 1998, 1849; M. Azad Malik, C. Byrom, P. O’Brien and M. Motevalli, Inorg. Chim. Acta, 2002, 338, 245.


4:00 PM PP7.7
Ultrathin Oxide Films: CaO Layers on BaO and SrO. Christopher E Mohn2, Neil L Allan2 and John Harding1; 1Engineering Materials, Univ. of Sheffield, Sheffield, United Kingdom; 2Dept of Chemistry, University of Bristol, Bristol, United Kingdom.

Nanostructure fabrication requires two-dimensional control of interfaces and the assembly of objects on the nanometre scale remains a primary objective in several fields. The manufacture of devices often demands the ability to exercise precise control over the growth of thin films on a host substrate. Indeed, atomic level definition may be required for applications such as supported superconductors, magnetic, optical and electronic devices. Using techniques such as molecular beam epitaxy, chemical vapour deposition and pulsed laser deposition,itis possible to produce phases that are very different from those found in the bulk , leading to new nanoscale materials and devices. Ultra thin oxide films. Such films are of interest in diverse fields ranging from catalysis to the development of new oxide gate dielectrics. We examine the form of the islands formed by CaO on BaO and SrO substrates using both periodic density functional theory and atomistic simulation techniques. (100) edges dominate the shape of the islands and we discuss in detail how the CaO layer adjusts to the substrate. Once formed, islands with intact edges remain intact. These are markedly different from CaO layers in bulk CaO and also from free CaO layers. Corner O atoms are associated with particularly short Ca-O bond lengths. There are few differences between islands formed on BaO and those on SrO. The cases we have examined are thermodynamically unstable but kinetically stable with respect to forming pillars, at least for small islands.


4:15 PM PP7.8
Single-Crystal Thin Films of SrFeO2 with FeO2 Infinite Layers. Yuichi Shimakawa, Satoru Inoue, Masanori Kawai, Monika Iwanowska and Noriya Ichikawa; Institute for Chemical Research, Kyoto University, Uji, Kyoto, Japan.

Square-planar oxygen coordination of Fe2+ is extremely rare because iron ions are favorably coordinated by oxygen irons tetrahedrally or octahedrally. Recently SrFeO2 with “infinite layers” of Fe2+O2 was reported to be synthesized by a low temperature treatment of SrFeO2.875 (Sr8Fe8O23) with CaH2 [1]. We have succeeded in preparing single-crystal thin films of SrFeO2 by using CaH2 for low-temperature reduction of epitaxial SrFeO2.5 single-crystal films deposited on KTaO3 and SrTiO3 substrates by a pulsed laser deposition method [2]. This reduction process, removing oxygen ions from the perovskite structure framework and causing rearrangements of oxygen ions, topotactically transforms the brownmillerite SrFeO2.5 to c-axis oriented SrFeO2. Attempts for preparing other single-crystal thin films of infinite layer oxides such as SrCoO2 and LaNiO2 are also reported. [1] Y. Tsujimoto, et al., Nature 450, 1062 (2007). [2] S. Inoue, et al., Appl. Phys. Lett. 92, 161911 (2008).


4:30 PM PP7.9
Periodic Nanopatterning using Spontaneous Phase Separation in Li-Containing Perovskite Oxides. Beth S. Guiton1, Hui Wu2 and Peter K Davies1; 1Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania; 2Center for Neutron Research, NIST, Gaithersburg, Maryland.

Solid state self-assembly has recently emerged as an intriguing approach to the spontaneous formation of nanostructures. Using this method researchers have been able to get tantalizingly close to achieving an “ideal” structure, which forms a spontaneous nano-scale pattern, with uniform and tunable periodicities, and controllably modulated properties. Here we present a remarkable structure in which spontaneous phase separation results in highly periodic checkerboard-like patterns formed by two phases whose dimensions both extend to the nano-scale. This occurs in the lithium-containing perovskite solid solution with the formula (Nd2/3-xLi3x)TiO3 to give Li-rich and Li-poor end members. We have demonstrated that this two-dimensional checkerboard pattern extends across entire crystal grains, and the supercell dimensions are tunable by choice of composition. By introducing chemical substituents we are able to produce an array of one- and two-dimensional nanostructures with a range of periodicities. These structures demonstrate potential for controllably modulating the electronic and magnetic characteristics of the material, and also the chemical reactivity at the surface - features which both could lead to exotic bulk properties, and could be exploited for use as nano-scale templates.


4:45 PM PP7.10
Nano-Scale Hydration of a Model Clay: NMR Studies. Romulo P Tenorio2, Lars R Alme1, Mario Engelsberg2, Jon Otto Fossum1 and Fernando Hallwass3; 1Department of Physics, Norwegian University of Science and Technology, Trondheim, Norway; 2Departamento de Física, Universidade Federal de Pernambuco, Recife, Pernambuco, Brazil; 3Departamento de Química Fundamental, Universidade Federal de Pernambuco, Recife, Pernambuco, Brazil.

Clays represent nano-materials with important environmental impacts. In order to understand better clay-water interactions at the nano-scale, we have used proton and deuterium NMR measurements to study smectite clay powdered samples. The results are compared with NMR data from other clays of the same family, as well as with recent results of molecular simulations. Water has the ability to intercalate stepwise into the nano-porous layered structure of such smectite nano-layered particles (hence, the term water layers [1]). The results yield new information about factors governing structure and dynamics of intercalated water in these materials: In the one-water layer regime, we have identified two different sites for the water. Further, we have observed proton exchange which seems to be promoted by a considerable amount of intercalated water outside of the hydration sphere of intercalated Na cations in the model clay fluorohectorite [2]. References: [1] G.J. da Silva, J.O. Fossum, E. DiMasi, K.J. Måløy, S.B. Lutnæs, Phys. Rev.E 66, 011303 (2002) - G.J. da Silva, J.O. Fossum, E. DiMasi, K.J. Måløy, Phys. Rev.B 67, 094114 (2003) [2] Rômulo P. Tenório, Lars Ramstad Alme, Mario Engelsberg, Jon Otto Fossum, Fernando Hallwass, J. Phys. Chem. C 112, 575-580 (2008)


 

SESSION PP8: Poster Session: Porous Materials
Chair: Catherine Murphy
Wednesday Evening, December 3, 2008
8:00 PM
Exhibition Hall D (Hynes)


PP8.1
Breathing and Twisting: Two Different Deformation Mechanisms of a Nanoporous Vanadium Benzenedicarboxylate. Xiqu Wang, Lumei Liu and Allan J Jacobson; Chemistry, University of Houston, Houston, Texas.

The microporous vanadium benzenedicarboxylate (VOBDC) belongs to the third-generation of nanoporous materials with flexible or “dynamic” frameworks that respond to changes in absorbed guests and external conditions. The VOBDC framework consists of chains of trans corner-sharing VO6 octahedra that are cross-linked by benzenedicarboxylate ligands. The 1D channels have a diamond shaped section outlined on each side by V-O2C(C6H4)CO2-V walls. The walls are flat when the channels are empty. Upon absorption of molecules such as acetone the channels reversibly close by changing the C-C-O-V torsion angle, and the walls bend to an “S” shape. This deformation has been extensively studied and named “breathing” first by Férey and coworkers. We have observed another deformation mode of the VOBDC framework when its channels are loaded with bulkier molecules such as cyclohexane. Two columns of cyclohexane molecules are packed in each channel of the VOBDC framework. To accommodate the guests, the channel expands along one wall direction and shrinks along another by cooperative rotations or twisting of the octahedral chains. This twisting mode bends the channel walls to a “C” shape. Various combinations of the breathing and twisting modes of deformation are observed by systematically changing the absorbed guest molecules.


PP8.2
Hydrothermal Synthesis and Structures of Novel Lanthanum Benzenedicarboxylates. Paola Gil-Mateo, Xiqu Wang and Allan J Jacobson; Chemistry, University of Houston, Houston, Texas.

Three novel lanthanum benzenedicarboxylates La2(bdc)3(H2O)4 1 , La3(OH)5(bdc)2 2 , and La4(OH)6(bdc)3 3 , (bdc = 1,4-benzenedicarboxylate) were synthesized by hydrothermal reactions and their structures determined from single crystal X-ray diffraction. All three compounds feature 3D framework structures consisting of layers of LaOn polyhedra cross-linked by bdc ligands along the layer stacking direction. In 1 the layers contain separated [LaO6(H2O)2] polyhedra that are bridged by the carboxylate groups of bdc. Compounds 2 and 3 both have highly condensed lanthanum hydroxide layers characterized by a single layer of closest-packed La3+ ions with the triangle interstices partially filled by OH groups. In 2 the layers comprise of [LaO3(OH)5] and [LaO4(OH)5] polyhedra that share common faces and edges. In 3 the layers are wavy and consist of [LaO5(OH)4] and [LaO4(OH)5] polyhedra that also share common faces and edges. Measurements of the optical properties will be reported.


PP8.3
Solvothermal Synthesis and Structural Characterization of Novel Metal-Triazolate Coordination Polymers. Hyunsoo Park, Gregory J Halder and John A Schlueter; Materials Science Division, Argonne National Laboratory, Argonne, Illinois.

Research in organic-inorganic hybrid solids has resulted in a tremendous amount of interesting structures in the recent years. Many of them have been studied for potential applications in gas storage, catalysis, magnetism and luminescence. Our research is aimed at finding new three-dimensional porous coordination polymers which are constructed using polyazaheterocyclic molecules as ligands and examining their capacities as gas storage materials. In this work, we report the solvothermal synthesis, structural chemistry and gas sorption characteristics of several new metal-organic hybrid coordination polymers constructed from transitional metal cations and 1,2,4-triazole. For example, zinc sulfide triazolate, Zn4S(C2H2N3)3(SCN)3, has been successfully synthesized solvothermally using 3-mercapto-1,2,4-triazole as an organic linker. Its crystal structure is based on the tetrahedral SZn4 clusters, which are connected to each other via Zn - triazole linkages. The resulting void space is occupied by thiocyanate anions which are coordinated to Zn atoms.


PP8.4
Thin Film of Flexible Porous Metal-Organic-Frameworks by Dip-coating Method. Patricia Horcajada2, Christian Serre1, David Grosso2, Cedric Boissiere2, Sandrine Perruchas3, Clement Sanchez2 and Gerard Ferey1; 1University of Versailles, CNRS, Versailles, France; 2Universite Pierre et Marie Curie, CNRS, Paris, France; 3Ecole Polytechnique, CNRS, Paris, France.

Porous metal-organic frameworks (MOF) combine a high and regular porosity and the presence of organic groups inside network. The easy tuning of the size, shape and composition offers a unique environment for the host-guest chemistry. Moreover, our group has recently reported a new class of flexible hybrid solids which modulate their pore size upon adsorption of organic molecules.[1] This reversible “breathing” effect varies between 50 and 235 % of volume cell unit, depending on the structure and the length of the linker. These characteristics allow the potential application of these bulk solids in very important fields as gas storage, drug release, separation or catalysis.[2] Making thin films of MOFs would of a high interest due to the enormeous prospects in nanotechnology for such films but examples are still quite scarce. To date, only a few studies have been reported dealing with the nucleation of MOF particles on substrate such as the work reported by Fischer et al.[3] on the selective nucleation and growth of MOF-5 on a modified Au substrate. We proposed for the first time a simple dip-coating method for the preparation of optical quality thin film of a porous flexible MOF. The porous hybrid solid MIL-89[4] (MIL: Material Institut Lavoisier) is built up from trimers of iron(III) octahedral linked to muconate dianions to create a 3D framework with a 1D pore channel system. The structure of MIL-89 is highly flexible and can swell, according to the nature of the adsorbed molecules, up to 160% in volume with a maximum pore size ≈11 Å. Homogeneous thin films of MIL-89 have been obtained by deposition of colloids using the dip-coating method. The evolution of particle size and the study of the crystallisation MIL-89 phase have been investigated. Finally, the flexibility of the resulting film was studied by environmental ellipsometric porosimetry[5] and indicated a reversible increase in thickness upon adsorption of water.[6] References. 1. Serre C., Mellot-Draznieks C., Surblé S., Audebrand N., Filinchuk Y., Férey G., Science, 315, 1828 (2007) 2. Li, H., Eddaoudi, M., O’Keeffe, M. & Yaghi, O.M. Nature 402, 276 (1999) 3. Hermes S., Schröder F., Chelmowski R., Wöll C., Fischer R.A., J. Am. Chem. Soc., 127, 13744 (2005) 4. Serre C., Millange F., Surblé S., Férey G., Angew. Chem. Int. Ed., 43, 6285 (2004) 5 S. Lepoutre S., Nicole L., Bruneau A.B., Sanchez C., Langmuir, 21, 12362 (2005) 6. P. Horcajada, C. Serre, D. Grosso, C. Boissiere, S. Perruchas, C. Sanchez, G. Férey, submitted (2008)


PP8.5
Abstract Withdrawn


PP8.6
Design of Porous Solids from Carboxyimidazoles and Carboxypyridines. John C. MacDonald, Lisa S Lee, Timothy J Lawton, Yu Wang and Mehmet V Yigit; Department of Chemistry & Biochemistry, Worcester Polytechnic Institute, Worcester, Massachusetts.

Porous crystalline solids that derive their porosity from rigid metal-organic frameworks of molecules are of interest because these materials exhibit large pore volumes, permanent porosity, high thermal stability and have pores with tunable structures and sizes. Consequently, framework solids show promise for application in storage, separation, and sensing of molecules. We currently are investigating the design and synthesis of several families of carboxyheterocycles that promote divergent assembly for this purpose. The structures and properties of porous crystalline solids prepared from carboxyimidazoles and carboxypyridines will be presented along with considerations for the design of porous frameworks.


PP8.7
In situ X-ray Diffraction Studies of Host-guest Properties in Nanoporous Metal-organic Framework Materials. Gregory Halder1, Karena W Chapman2, Hyunsoo Park1 and John A Schlueter1; 1Materials Science Division, Argonne National Laboratory, Argonne, Illinois; 2X-ray Science Division, Argonne National Laboratory, Argonne, Illinois.

The accurate elucidation of the often complex structure-function relationships in functional porous materials, such as metal-organic frameworks (MOFs) and other advanced materials, presents a crucial step in their advancement toward becoming industrially important porous materials. This requires the development of in situ structural techniques, such as X-ray diffraction, to precisely monitor the structural response of materials under the conditions in which they perform their desired functions. While the implementation of in situ techniques can be challenging, they promise an unparalleled insight into not only major structural changes, such as phase transformations, but also many other more subtle structural variants, such as those associated with the rearrangement of host-guest interactions. Here, we present structural studies of the host-guest properties in a range of porous MOF materials, including systems that incorporate guest-despendent electronic switching centers (spin crossover).


PP8.8
Nitrogen and Krypton Adsorption Characterization of Nanostructures Fabricated with Glancing Angle Deposition. Katie Krause1, Michael T Taschuk1, Matthias Thommes2 and Michael J Brett1,3; 1Electrical and Computer Engineering, University of Alberta, Edmonton, Alberta, Canada; 2Quantachrome, Boynton Beach, Florida; 3National Research Council National Institute for Nanotechnology, Edmonton, Alberta, Canada.

Nanostructured porous thin films fabricated by glancing angle deposition (GLAD) have been characterized in terms of surface area and pore size distribution using adsorption of krypton and nitrogen gas. GLAD is a single-step physical vapor deposition technique which, through the use of substrate rotation and oblique incident vapor flux, allows for the fabrication of structured thin films from a range of organic, metallic, and dielectric materials [1]. Knowledge of surface area and porosity will enable optimization of these coatings for use in sensing, microfluidic, and catalyst development. Gas adsorption porosimetry using nitrogen gas at 77.4 K is commonly used for studying the porosity of porous powder and thin films samples [2]. However, due to its high saturation pressure, nitrogen gas does not offer a means to detect the small pressure changes seen during gas adsorption on low surface area samples (such as thin films deposited on silicon wafers). Instead, krypton gas can be used at 77.4 K and 87.3 K due to its low vapor pressure in order to obtain high sensitivity gas adsorption measurements [3, 4]. For the current work we carried out krypton gas adsorption at 77.4 K, the standard temperature for measuring surface area using the Brunauer Emmett and Teller (BET) method, and 87.3 K, used for pore size distribution over a wider krypton solidification-free pressure range than that offered at 77.4 K, to determine porosity characteristics of low, moderate, and high surface area obliquely deposited thin films. We also carried out nitrogen adsorption at 77.4 K on selected high surface area samples in order to compare the surface area findings to those obtained through krypton adsorption. We present the specific surface area, surface area enhancement, and pore size distribution results as functions of the deposition angle for GLAD thin films fabricated from a range of materials. Findings indicate extremely high surface area thin films, approaching 1000 times the footprint area for a one micron film, can be constructed using the GLAD technique. The results are compared against the simulation and experimental results obtained previously [5, 6, 7]. 1 M.M. Hawkeye, M.J. Brett, Journal of Vacuum Science Technology A, 25, 1317-1335 (2007). 2 S. Lowell, J.E. Shields, M.A. Thomas, M. Thommes, Characterization of porous solids and powders: Surface area, pore size and density, Springer, The Netherlands (2006). 3 G.Q. Lu, X.S. Zhao, eds., Nanoporous Materials: Science and Engineering, Imperial College Press, Chapter 11 (2004). 4 M. Thommes, N. Nishiyama, Shunsuke Tanaka, Recent Progress in Mesostructured Materials, 551-554 (2007). 5 M. Suzuki, Y. Taga, Journal of Applied Physics, 90, 5599-5605 (2001). 6 M.C. Demirel, Colloids and Surfaces A: Physicochemical and Engineering Aspects, 321, 121-124 (2008). 7 C.-C. Li, J.-L. Huang, R.-J. Lin, D.-F. Lii, C.-H. Chen, Journal of Vacuum Science Technology A, 25, 1373-1380 (2007).


PP8.9
Macropore Formation in a Prepatterned P-type Silicon and Anodic Oxidation Effect on Macropore. Jae Hyun Kim1, Kang Phil Kim1, Hong Seok Suh2 and Jung Ho Lee2; 1Division of Nano & BioTechnology, Daegu Gyeongbuk Institute of Science and Technology, Daegu, South Korea; 2Department of Materials and Chemical Engineering, Hanyang University, Ansan, South Korea.

When high aspect ratio structures are required, it is easily established by forming deep macropores or trenches in an n-type silicon substrate as described by Lehmann. However, such a deep macropore formation in p-type silicon is more difficult than in n-type silicon because there exists an ambiguity in space-charge region to control the diffusion of holes to the pore tips for anisotropic dissolution of silicon, and passivation of pore walls against dissolution. In order to produce periodically arranged pores, the wafer surface must be structured prior to the etching by a standard photolithography. Although there have been several reports about random macropore formation, few reports concerning the ordered macropore formation of high aspect ratio with a smooth side interface have been published. Ordered macropore of smooth wall surface is formed mainly in electrolyte of HF: deionized water:2-propanol with a composition of 5:6:29 in volume, which is non-organic etching solution. In the present study, we have undertaken a systematic study of the solvent effects in mixtures of HF with various composition of dimethyl sulfoxide (DMSO), in order to understand the role played by the organic solvent in the dissolution reaction at the silicon/electrolyte interface and in the limiting conditions of macropore formation. We have also conducted an experiment about the diameter increase of formed macropore by anodic oxidation. To produce well ordered macropore, an initial structure of ordered pitches has been produced by a preceding photolithographic process using standard potassium hydroxide (KOH) etching. The type of pattern is fabricated in 5 um square holed at a distance of 2 um. P-type silicon (10 ~ 15 Ω−cm, (100) oriented) was used. It is usual that the side of pore wall is very rough in the case of random macropore formation when HF solution with organic such as DMSO, DMF was used for electrochemical etching of p-type silicon. This is the same phenomenon as ordered macropore formation. The interface of wall in the macropore obtained in HF:DMSO (7:43) electrolyte was very rough and has branches shorter than pore diameter. In contrast, the macropores in HF:DMSO:DI(1:5:5) solution, in which the content of water increases, has well defined microstructures with a very smooth interface of wall. The pore width is almost constant from the surface of wafer to pore tip. The anisotropic etching in Si has been well investigated by infrared absorption spectroscopy, explaining the electrochemical behaviors of the silicon/electrolyte interface. We focused on the effect of the different composition of organic solution on macropore formation. We have observed that the widening of macropore width by repetitive anodic oxidation. By 5 cycles of anodic oxidation and etching of silicon oxide on the surface of silicon macropore, half of width of original macropore has been obtained.


PP8.10
Abstract Withdrawn


PP8.11
Abstract Withdrawn


PP8.12
Abstract Withdrawn


PP8.13
Synthesis of Porous Biomorphic Cu/CeO2/Al2O3 by using Cotton as Templates. Ka Lok Chiu1, Fung Luen Kwong1, Juncai Jia2, Jia Li3 and Dickon Hang Leung Ng1; 1Physics, The Chinese University of Hong Kong, Hong Kong, China; 2Chemistry, The Chinese University of Hong Kong, Hong Kong, China; 3Material Science and Engineering, University of Jinan, Jinan, China.

Methanol has high volumetric energy density and is relatively easy to handle, thus methanol fuel cells have potential applications in automobiles and portable devices. There are two types of methanol fuel cells. The direct type cell oxidizes methanol for power generation while the indirect type first converts methanol to hydrogen and uses it as fuel. Indirect methanol fuel cell has several advantages. It has a higher efficiency compared to the direct type, and does not need hydrogen supply and storage as in the hydrogen fuel cell. However, its size is larger and it is heavier as reforming methanol and removing CO are required. Meanwhile, the catalyst with mechanical support such as ceramic foam or honeycomb accounts for a significant part of its total weight. Thus, its applications are limited, especially in portable devices. As a remedy, we have developed a high surface area/weight ratio, low cost and self-supported catalyst for the indirect methanol fuel cell by using porous biomorphic Cu/CeO2/Al2O3. This ternary system is produced via a chemical method by using cotton as templates. Cu/CeO2 is a catalyst for reforming methanol and for oxidation of CO, and the Al2O3 is to prevent segregation of the Cu and CeO2 fine particles. To prepare this biomorphic Cu/CeO2/Al2O3, a 0.5 M Boehmite solution was prepared with C9H21O3Al via the Yoldas process. It was then mixed with 0.5 M Cu(NO3)2 and 0.5 M Ce(NO3)3 solutions. The weight percentage ratio of Cu:Ce:Al was 3:2:5 in the mixture. Cotton balls were soaked in the mixture, and they were air dried before sintered in air at temperatures ranged from 400oC to 1000oC. The sintered samples were further reduced with diluted hydrogen at 250oC for 2 hours. The final products were characterized via SEM, TEM, XRD, BET, DTA and TGA. We found that the products maintained the original macroscopic shape and size of the cotton ball and no obvious shrinkage was observed. The SEM images showed that the original internal fibrous networks in the raw cotton was retained in the biomorphic product, however, the fibers became hollow. The XRD result confirmed that the Cu/CeO2/Al2O3 compound was produced when the sintering temperatures between 500oC and 700oC. The sizes of the Cu and CeO2 particles in the products were in nanometer scale. When the sintering temperature was higher than 700oC, CuAl2O4 was produced. When temperature was below 500oC, Cu2O was produced. From the DTA and TGA results, the pyrolysis of soaked cotton occurred between 190oC and 380oC. The sample weight decreased to about 16% of its original at 380oC, and kept almost constant at higher temperatures. The BET area of our products was about 100m2 per gram, which was comparable to those of similar products synthesized by other methods. Our products are self supported and mechanical support was not required. It is expected that the weight of catalysts can be greatly reduced and the energy utilization of the indirect methanol fuel cell can be improved.


PP8.14
Characterization of Nonlinear Optical Materials Using Brooker's Merocyanine in Microporous Zeolites. Jennifer S. Holt1 and Casandra Sheldon2; 1School of Science - Chemistry, Penn State Erie, The Behrend College, Erie, Pennsylvania; 2Dept. of Chemistry, Miami University, Oxford, Ohio.

The use of nanoporous materials has become increasingly practical in the pursuit of novel composite materials with nonlinear optical properties. Specifically, the straight channels (5.7 Å) of the MFI zeolite framework can be used to align dye molecules in a noncentrosymmetric arrangement that is necessary for second-harmonic generation (SHG), also known as frequency doubling. This study focused on generating new SHG materials using host-guest chemistry, where Brooker’s merocyanine (BM) dye molecules were the guests within silicalite and ZSM-5 zeolite hosts. Brooker’s merocyanine is a highly conjugated, zwitterionic, dye molecule that exhibits a large molecular hyperpolarizability, which is necessary for SHG response. ZSM-5 and silicalite are structurally equivalent microporous MFI zeolites, but they have different chemical compositions, which leads to different hydrophilic/hydrophobic characteristics. SHG was observed in the BM/ZSM-5 powder sample, but not in the BM/silicalite powder. Using solution and solid-state UV/Vis and fluorescence spectroscopy, the extent of dye loading was determined for each system. Although dye was adsorbed to both zeolites, the degree of dye loading was much larger for the BM/ZSM-5 powders. The location of dye in both systems (surface coverage vs. interior channels) was determined using simple models and justified using BET analysis. These results were consistent with the overall model developed for these materials, which indicated that the dye was inserted into the channels of ZSM-5, but it only coated the surface of the silicalite crystallites. Finally, the BM/ZSM-5 powders were prepared from different solvents, and thin films of BM/ZSM-5 were prepared and characterized in order to optimize the dye loading, ordering and SHG.


PP8.15
Studying the Formation of Ti-Beta Zeolitic Nanoparticles and Preparation of Microporous/mesoporous Composites with Ti-Beta and MCM-41, MCM-48 or SBA-15. Venceslav Kaucic, Mojca Rangus, Matjaz Mazaj and Gregor Mali; Inorganic, National Institute of Chemistry, Ljubljana, Slovenia.

Microporous zeolitic nanoparticles, such as titanium-containing nanoparticles of zeolite Beta, can be used for preparation of microporous/mesoporous composite materials. Composite materials combine advantages of both types of their constituents, stable catalytic sites of microporous domains and rapid diffusion of molecules through mesoporous domains. In order to successfully incorporate microporous particles into walls of mesoporous material or to deposit them into mesopores themselves, these zeolitic particles need to be small enough. This means that the zeolite synthesis has to be stopped as soon as the particles exhibit characteristic zeolitic structure. In this contribution we present our studies of formation of Ti-Beta particles by 29Si solid-state and liquid-state NMR spectroscopy, by IR spectroscopy and by X-ray powder diffraction and high-resolution transmission electron microscopy. With these techniques we monitored zeolite formation from the initial precursor gel to the final Ti-Beta product. We found out that larger silica clusters start to form early in the Ti-Beta synthesis procedure. After 6 hours of hydrothermal treatment silica hexamers and octamers were already observed and with the increasing time of hydrothermal treatment, the amount of Si monomers and dimers decreased along with the increase of higher silica polymers. After approximately 30 hours of hydrothermal synthesis Ti-Beta particles reached the size of about 5 nm. Using the knowledge about the growth of Ti-Beta nanoparticles, we were then able to prepare thermally stable titanium-containing microporous/mesoporous composites Ti-Beta/MCM-41 and Ti-Beta/MCM-48. The interconnection of the microporous and either hexagonal or cubic mesoporous domains, i.e. the incorporation of microporous nanoparticles into mesoporous walls, was determined by high-resolution TEM investigations in combination with electron and X-ray diffraction. Adsorption properties obtained by alpha(s)-plot analysis of nitrogen adsorption isotherms confirmed the small size of the Ti-Beta domains present in the composite materials. Very recently we have also prepared Ti-Beta/SBA-15 composite, in which, as opposed to the composites mentioned above, Ti-Beta nanoparticles were simply deposited into mesopores of previously prepared SBA-15.


PP8.16
Abstract Withdrawn


PP8.17
Abstract Withdrawn


PP8.18
Manipulating Colloids and Surfactant as Co-Templates for Hierarchically Porous Nanostructures and Nanocomposites. Fan Li, Zhiyong Wang, Sarah A Delo and Andreas Stein; Chemistry Department, University of Minnesota, Minneapolis, Minnesota.

Templating is a general and efficient strategy for creating nanoporous materials. Different pore architectures and dimensions have been achieved with various templates. Two commonly employed classes of templates are colloidal crystals and surfactants. Colloidal crystals typically have an opal-like structure and have been used to produce three-dimensionally ordered macroporous (3DOM, >50 nm pores) solids; surfactants generate various ordered mesoporous structures (2-50 nm pores) as a result of their versatile self-assembly behavior. Combining colloidal crystals with surfactants realizes simultaneous templating at two length scales and leads to materials with hierarchical pore architectures, opening a door towards design and functionalization of new complex materials. One aim of this study is to fully understand the mutual influence between the two templating systems using a series of hierarchically structured porous materials synthesized via dual templating. A second aim is to create novel nanostructures and nanocomposites with designed pore hierarchy based on this dual templating approach. We conducted comprehensive TEM characterization of different hierarchically-ordered porous silica samples to reveal how the macro- and mesostructures are integrated within a single unit. Especially, we detailed hierarchically porous structures with two distinct sets of columnar mesopores, these being either perpendicular or parallel to the macropore walls. Based on TEM observations and computational simulation, we correlated the different mesopore structures to the surfactant phase behavior within the colloidal crystal confinement. The mesopore orientations are functions of the mesostructure dimensions, the interstitial space in the colloidal crystal, interfacial interactions, entropic effects, and structural frustration. A thorough understanding of the hierarchically porous structure will help to elucidate the interplay of different templating methods and will also benefit technological applications of the materials in many fields.


PP8.19
Abstract Withdrawn


PP8.20
Synthesis and Characterization of Lead Telluride Gels and Aerogels. Shreyashi Ganguly and Stephanie L Brock; Chemistry, Wayne State University, Detroit, Michigan.

Aerogels are unique class of inorganic polymers that feature a highly porous internal structure which translates into extremely high specific surface areas, low densities and low thermal conductivities. These properties make aerogels well-suited for applications as catalysts, sensors and thermal insulators. The chemistry underpinning aerogel formation has been well developed for oxide systems, particularly silica. Recently, we successfully developed a sol-gel protocol that enables metal chalcogenide aerogels to be prepared, and demonstrated this approach for PbS, CdSe, ZnS, PbSe and CdSe/ZnS systems. The general procedure for metal chalcogenide aerogel formation involves (1) synthesis of the discrete nanoparticles, (2) aggregation of the nanoparticles by controlled oxidation to form the gel network, and (3) drying using supercritical fluid extraction. The gels obtained are usually monolithic with “pearl necklace” type morphology and remain quantum confined despite the fact that they are linked together in a 3-dimensional network. Despite the unique properties noted in the sulfide/selenide systems, there is no report of this method being applied to telluride systems. The goal of the research is to extend the sol-gel protocol to PbTe, a material chosen because of its potential use for thermoelectric applications. Here we report the successful formation of PbTe nanoparticles and their transformation into gels and aerogels. The effects of the gelation agent on morphology and composition will be presented. Moreover, the suitability of these PbTe nanostructures for thermoelectric applications will be discussed.


PP8.21
Synthesis and Characterization of Ag2Se, CuSe, PbSe Gels and Aerogels by Cation Exchange Reactions. Qinghong Yao and Stephanie L Brock; chemistry, Wayne State University, Detroit, Michigan.

An aerogel is a unique class of material with a highly porous solid network composed of connected nanoscale building blocks. The presence of an interconnected network of pores with a high surface area nanostructure leads to many actual and potential applications, such as in catalysis, solar cells and sensors. Our group has synthesized a series of metal chalcogenide aerogels by sol-gel assembly of the corresponding metal chalcogenide nanoparticles together followed by supercritical solvent extraction. The obtained aerogels maintain the inherent nanoparticle properties, have average pore sizes in the mesoporous regime and very high surface areas. Among these aerogels, the synthesis of CdSe aerogel is well developed and the properties have been systematically studied. The present study describes a new synthesis method for generating new metal chalcogenide aerogels by cation exchange reactions of CdSe wet gels. Cation exchange reactions have been used previously as a simple method for preparing new compositions of nanoparticles, without having to build the new nanoparticle from the bottom-up. Since the metal chalcogenide aerogels are formed from nanoscale building blocks, we surmised that the cation exchange method should be an efficient way to form new aerogel compositions without the need to synthesize and assemble different building blocks. The synthesis of Ag2Se, PbSe, and CuSe wet gels is achieved by addition of Ag+, Pb2+ or Cu2+ cations to the CdSe wet gel. The resultant metal selenide wet gel was dried under supercritical conditions to yield the aerogel. In this presentation, the detailed synthesis procedure will be described. Additionally, the structural, optical and porosity characteristics of the obtained Ag2Se, PbSe, CuSe aerogels will be presented.


 

SESSION PP9: Poster Session: Nanomaterials
Chair: Catherine Murphy
Wednesday Evening, December 3, 2008
8:00 PM
Exhibition Hall D (Hynes)


PP9.1
A Crystallographically-Selective Chemical Transformation in Cadmium Sulfide Nanorods. Bryce Sadtler1,2, Denis O Demchenko3, Haimei Zheng2, Lin-Wang Wang3, Ulrich Dahmen2 and A. Paul Alivisatos1,2; 1Department of Chemistry, University of California, Berkeley, California; 2Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California; 3Computational Research Division, Lawrence Berkeley National Laboratory, Berkeley, California.

We have performed partial copper (I) cation (Cu+) exchange in cadmium sulfide (CdS) nanorods to produce asymmetric cadmium sulfide-copper sulfide (CdS-Cu2S) binary heterostructures. Nucleation of the CdS-Cu2S interface occurs selectively on the end faces of the nanorods and the Cu2S material grows inwards by further cation substitution. Asymmetric growth of Cu2S into the two ends of the nanorod is attributed to the non-centrosymmetry of the CdS wurtzite lattice, such that the crystalloraphically dissimilar (001) and (00-1) end faces have different reactivities towards cation substitution. The asymmetry can be adjusted by varying the dimensions of the initial CdS nanorods and the rate of addition of Cu+ cations. Modeling the CdS-Cu2S interface gives insight into the crystallographic selectivity of the cation exchange reaction. Models for the epitaxial attachment of chalcocite Cu2S to the (001) and (00-1) end faces of a wurtzite CdS nanorod result in a lower interface formation energy than attachment to the {100} CdS side facets. Furthermore, the asymmetry between Cu2S attachment to the (00-1) and (001) faces of CdS can be explained by differences between the surface and interface formation energies on the two ends of the nanorod.


PP9.2
Light Scattering by White-Emitting CdSe Nanocrystals and Traditional YAG:Ce3+ Phosphor Particles. Jonathan D Gosnell1,2 and Sharon M Weiss1,2; 1Interdisciplinary Graduate Program in Materials Science, Vanderbilt University, Nashville, Tennessee; 2Department of Electrical Engineering and Computer Science, Vanderbilt University, Nashville, Tennessee.

In order for solid state lighting technology to become a mainstream technology, one of the major challenges to overcome is increasing the efficiency of these devices while maintaining a proper color balance. A significant source of efficiency loss in commercial white light-emitting diodes is light scattering. The large diameter of the YAG:Ce3+ phosphor, generally 1-2 μm, leads to a substantial amount of scattering of the excitation light and subsequent re-absorption by the LED die. This can lead to a decrease in the overall device efficiency of up to 50%. The use of recently reported single-size CdSe white-light nanocrystals in place of the YAG:Ce3+ phosphor could lead to lower scattering losses and higher device efficiencies as a result of its extremely small core diameter of approximately 1.5 nm. This issue was explored both theoretically and experimentally for ultra-small CdSe white-light nanocrystals in comparison to common micron-sized phosphor particles. The absorption, scattering, and extinction coefficients and cross-sections were calculated for both types of particles using simulations based on the Rayleigh approximation and Mie theory of scattering. Both Mie and Rayleigh scattering were used for the much smaller CdSe nanocrystals while only Mie scattering was used for the larger phosphor particles. Experiments were performed using thin films of encapsulated nanocrystals and phosphor particles. The films were prepared using a variety of silicone and polymer encapsulants, different concentrations of nanocrystals or phosphor particles, and varying film thicknesses. By measuring the absorbance and thickness of the films, in addition to the concentration of the nanocrystals and particles, the extinction coefficients and cross sections were determined using Beer's Law. Similarly, measurements of the reflectance of the films and their thicknesses allowed for the calculation of the absorption and scattering coefficients and cross sections. As expected, the size of the particle has a significant impact on the extinction, absorption, and scattering properties of the thin films. For example, the theoretical scattering cross section for the CdSe nanocrystals at 420 nm was found to be on the order of 10-19 cm2, while for the YAG:Ce3+ phosphor at 450 nm it was found to be on the order of 10-8 cm2. A reasonable agreement was obtained between theoretical and experimental data. The considerably reduced scattering from the nanocrystals compared to traditional phosphors, along with their inherent high quality white light emission, makes them a promising candidate for future solid state lighting applications.


PP9.3
Single Step Synthesis of Y2O3:Eu3+ Nanophosphor Prepared by Flame Spray Pyrolysis. Jae Seok Lee1, Purushottam Kumar1, Sejin Kim1, Madhav B Ranade2 and Rajiv K Singh1; 1Materials Science of Engineering, University of Florida, Gainesville, Florida; 2Particle Engineering Research Center, University of Florida, Gainesville, Florida.

A novel ceramic synthesis technique, flame spray pyrolysis (FSP) was investigated for the production of nanophosphor particles. Among the various types of synthesis technique for phosphors, FSP is a powerful method which is capable of producing particles with good crystallinity and high luminescence efficiency. Red light emitting Eu3+ doped Y2O3 nanophosphor was prepared by FSP from nitrate based liquid precursors with high flame temperature. Flame temperature is an important factor to obtain phosphor particles with dense and spherical shape. Different molar percentage of urea was added into the precursor, addition of urea increases the temperature in the flame zone and promotes the formation of nano-size and spherical shaped particles. The importance of urea in the precursor to obtain well dispersed Y2O3:Eu3+ nanophosphor has been studied. The characteristics of nanophosphor such as crystallinity, morphology and photoluminescence in the presence of different moles of urea in nitrate based aqueous solution were investigated. On varying the overall concentration of the precursor, both the optical properties and crystallinity were investigated. XRD spectra showed as-prepared phosphors were obtained directly as cubic phase Y2O3:Eu3+ nanophosphor with high crystallinity and without any post-heat treatments. Luminescence intensity of nanophosphor increased with the amount of urea till 2 molar percentages, further increase in urea concentration was found to reduce the PL intensity. We have developed a continuous single-step fabrication method for nanocrystalline Y2O3:Eu3+ nanophosphor without any post-heat treatments procedure.


PP9.4
Ternary I-III-VI Quantum Dots Luminescent in the Red to Near Infrared. Peter Allen, Gautham Nair and Moungi G Bawendi; Chemistry, MIT, Cambridge, Massachusetts.

We present a modular synthetic strategy for the synthesis of ternary I-III-VI semiconductor nanocrystals, or Quantum Dots (QDs). Previous luminescent QD materials systems have been primarily restricted to binary II-VI, III-V, and IV-VI semiconductors. In this work we present the synthesis and characterization of luminescent Cu-In-Se QDs with band gaps tunable over the red to near infrared region. We report band edge, or near band edge, photoluminescence (QYs up to 25%) from Cu-In-Se QDs, in sharp contrast to bulk Cu-In-Se semiconductors where band edge photoluminescence is rarely observed at room temperature. The atomic structure of the Cu-In-Se QDs is probed by X-ray diffraction studies. We find the crystalline structure of various stoichiometries of Cu-In-Se QDs is consistent with a family of ordered vacancy chalcopyrite compounds. We examine the nature of light emission by temperature dependent photoluminescence measurements. Also, we demonstrate the modularity of the synthetic method with the synthesis of novel Ag-In-Se QDs with luminescence from orange to red. The extension to Ag-In-Se QDs demonstrates this synthetic method may be amenable to the synthesis of other I-III-VI QD systems allowing for further exploration of the elemental compositions and electronic properties in QD materials.


PP9.5
Nonlinear Optical Properties of Lead Sulfide Nanocrystals Grown in the Presence of Polymers. Daniel J. Asunskis, Igor L Bolotin and Luke Hanley; Chemistry, University of Illinois at Chicago, Chicago, Illinois.

PbS nanocrystals, a group IV-VI semiconductor, have a size-tunable band gap and have potential as photovoltaics, photodiodes, nonlinear optical devices, and other applications. PbS nanocrystals with large nonlinear absorption coefficients have been synthesized, where the crystals were grown directly in the presence of the polymer. The conjugated polymer poly(2-methoxy-5-(2’-ethyl-hexyloxy)-p-phenylene vinylene (MEH-PPV) and optically clear polymers: polyethylene, poly(1-butene), poly(1-decene) and polystyrene were used in this synthesis. The polymer acts as the sole growth limiting agent in the synthesis of the nanocrystals. The average sizes of the nanocrystals ranged from 4 to 9 nm for the different polymers. These polymers do not have functional groups that can interact and bond with the nanocrystals during growth, giving rise to a unique nanocrystal surface. The analysis of the nonlinear optical properties was done using the z-scan method. Strong nonlinear absorption was observed in open aperture z-scan measurements conducted at both 1064 and 532 nm. The normalized z-scan traces for all five nanocomposites showed an initial onset of saturable absorption at low laser fluence followed by strong reverse saturable absorption as the scan progressed through the focussed laser pulses during analysis. Studies were carried out using a pulsed laser, with a repetition rate of 10 Hz and pulse duration of 4 ns. Maximum peak intensities of 108-109 W/cm2 were used in the analysis. The z-scan data was fitted using a function based off a two photon absorption model. The best fit to the experimental data gave high values of the nonlinear absorption coefficient, β, in range of 100-200 cm/GW. Changes in the β value for these five composites showed no evident dependence with the size changes in the nanocrystals. These composites have strong differences in nonlinear optical activity when compared to nanocrystals grown in strongly bonding environments, such as surfactant capped nanocrystals or nanocrystals grown in the presence of polymers with attached functionality, such as PVA. This can be understood when considering that the optical properties of the nanocrystal are strongly attributed to the surface properties of the nanocrystal. The results for the nonlinear optical measurements on the five newly synthesized nanocrystal/polymer composites will be discussed along with the surface properties that lead to the nonlinear activity.


PP9.6
Factors Influencing Phase Stability in the Formation of Fe-P Nanoparticles. Elayaraja Muthuswamy and Stephanie L Brock; Chemistry, Wayne State University, Detroit, Michigan.

Iron phosphides display a range of properties depending on their phase; Fe3P and Fe2P are ferromagnetic. FeP is metamagnetic and FeP2 is a semiconductor. These properties can be expected to vary with size when prepared with dimensions less than 100 nm. Accordingly, methods for the preparation of FeP and Fe2P on the nanoscale have been developed, including the thermal decomposition of precursors, conversion of metal nanoparticles into phosphides, and solvothermal reactions. However, the key factors that govern which phase is formed (Fe2P vs FeP) remain unresolved. In particular the possibility of secondary phase contamination has clouded the interpretation of magnetic data for these materials. The objective of this particular study is to investigate the factors that influence the formation of different phases and develop a simple synthetic strategy to prepare phase pure iron phosphide nanoparticles. In this presentation, the effect of temperature, time, and phosphorus precursor concentration on the phase of the final product generated from the thermal treatment of Fe nanoparticles with trioctylphosphine will be described and the specific factors that lead to phase pure samples of FeP and Fe2P will be discussed.


PP9.7
Electrochemical Analysis of RuO2 Nanoskins on SiO2 Filter Paper. Alia Marie Lubers, Christopher N Chervin, Jeremy P Pietron, Jeffrey W Long, Justin C Lytle, Katherine A Pettigrew and Debra R Rolison; Surface Chemistry Branch - Code 6170, Naval Research Laboratory, Washington, District of Columbia.

A flexible, lightweight, multifunctional electrode has been prepared by solution-based deposition of nanoscale shells of RuO2 (< 10-nm thick) onto the fibers of an insulating, SiO2 filter paper (RuO2//SiO2). The interconnected RuO2, which covers most of the fiber surfaces, comprises ~5% of the total weight and 0.1% of the total volume, yet the electrode exhibits a geometry-normalized conductivity of ~ 1 S cm-1 and a mass-normalized conductivity that exceeds that of bulk ruthenia. Here we present electrochemical properties of the RuO2//SiO2 nanocomposite in both aqueous (acid and base) and nonaqueous environments. The three dimensional, macroporous electrode displays large proton capacitance typical of hydrous RuO2 while maintaining high electronic conductivity found in polycrystalline RuO2. The simultaneous expression of these two physical properties is apparently related to the nanostructured morphology of the RuO2 coating on the SiO2 fibers. The surface area of the RuO2 coating, determined from the double-layer capacitance measured in nonaqueous electrolyte, is significantly greater at 150 m2 g-1 than that of cryogenerated RuO2 nanoparticles (cryo-RuO2). Additionally, we investigate the lithium-ion insertion properties of the RuO2//SiO2 electrode and compare the results with those we previously reported [1] for cryo-RuO2. Energy conversion is the primary motivation for developing this nanocomposite electrode and we also present results of modifying the RuO2//SiO2 with redox-active moieties for these applications. [1] J.C. Lytle, C.P. Rhodes, J.W. Long, K.A. Pettigrew, R.M. Stroud, and D.R. Rolison, J. Mater. Chem.17 (2007) 1292.


PP9.8
One Pot Synthesis of Nearly Monodispersed Silver Nanoparticles Using Biphenylphosphine Silver (I) Complexes. Selby Phumlane Mdluli1,3, Neerish N Revaprasadu1 and Damir A Safin2; 1Chemistry, University of Zululand, KwaDlangezwa, KwaZulu-Natal, South Africa; 2Chemistry, Kazan State University, Kremlevskaya 18, Kazan, Russian Federation; 3Project Autek, Advanced Materials Division,Mintek, Randburg, Gauteng, South Africa.

In this paper we report a versatile, very reproducible organometallic route for large scale synthesis of Hexadecylamine (HDA)-protected silver nanoparticles. This method is fast, reproducible and it was achieved by employing biphenylphosphine silver (I) complexes. The nanoparticles synthesized from this method offer the arresting property of good stability and lack of aggregation. Most of the synthesis reported to date rely on the usage of organic solvent and reducing agents like sodium borohydride and N,N-dimethylformamide. HDA is used as solvent, reducing and capping agent for preventing particles from aggregation. The HDA forms a hydrophobic surface and can only be easily dispersed into organic solvent. The HDA capped silver nanoparticles shows a strong absorption band at 402 nm. The HDA capped silver nanoparticles are spherical in shape with a particle sizes in the range from 10-20 nm. The X- ray diffractogram of the HDA capped silver nanoparticles shows resembling in the face centered cubic silver.


PP9.9
Rational Synthesis of Two-dimensional Structures of Noble Metals and Biomaterials by Tuning the Driving Force of Chemical Reaction: An Interpretation of Kinetic Control. B. Viswanath, Paromita Kundu and Ravishankar Narayanan; Materials Research Centre, Indian Institute of Science, Bangalore, India.

Understanding shape control during wet chemical synthesis is important for rational synthesis of nanostructures. Here, we show that two-dimensional (2D) metal structures can be obtained from metal salts by reducing the driving force of the reduction reaction that directly translates to the growth of the metal taking place through layer by layer mechanism. Experimental evidence is provided for Au, Ag, Pt and Pd systems by choosing appropriate reaction conditions without using any external surfactant. The results are analysed in terms of the calculations of driving force under different conditions. The results show that surfactants may not be important for producing shape control for the case of 2-D structures while they are required to obtain size control. It is shown that the regime of low driving force is also one where the kinetics of the process is slow and thus a new interpretation of the kinetic control hypothesis is provided. The idea has been extended for biomineralization also where 2D shaped crystal of hydroxyapatite (HA), CaCO3 and ZnO are synthesized.


PP9.10
Confined Synthesis of Metal (M = Cu, Ag, Au, Pd) Nanoparticles. George Harrison Thomas1, Sami Chanaa1, Michael Farinelli1, Paige Landry1, Ben Estes1 and John Z Larese1,2; 1Chemistry, University of Tennessee Knoxville, Knoxville, Tennessee; 2Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee.

1Thomas, G. H.; 1Chanaa, S.; 1Farinelli, M.; 1Landry, P.; 1Estes, B. E.; 1,2Larese, J. Z. 1Chemistry Dept., University of Tennessee, Knoxville, TN 37996 2Oak Ridge National Laboratory, Oak Ridge, TN Abstract: Colloidal suspensions of Cu, Ag, Au and Pd nanoparticles were synthesized using confined-growth methods. Our initial investigations were performed using dry Cu(NO3)2, AgNO3, H[Au(NO3)4] and Pd(NO3)2 as the metal precursors, tri-n-hexyl amine as both a solvent and reducing agent and oleic acid as the capping agent. While, initial results were promising, this method of attack proved unsuitable for the successful synthesis of nano-scale Au and Pd, resulting instead in the formation of uncontrolled aggregates of the respective metals. Interestingly, by using phenyl ether as a solvent and oleic acid as the surfactant/reducing agent Au and Pd nanoparticles were successfully produced from the respective nitrates. When Cu(NO3)2 ● X H2O is used as the Cu precursor Cu rich Cu2O is produced. Prolonged heating of this product results in the reduction of Cu1+ to Cu0. Although the particles were on the nm scale, they unfortunately would not remain in solution but readily formed aggregates instead. This observation led to the development of alternative synthetic routes using CuO, Cu2O, AgO and Au2O3 as the metal precursors for the synthesis of Cu, Ag and Au nanoparticles. Synthetic procedures using solvent/surfactant systems of tri-n-hexyl amine/oleic acid and phenyl ether/tri-n-hexyl amine/oleic acid were also investigated. Finally, if time permits, we will discuss our results using AgNO3 and Ag2O as model metal precursors and the effect on the synthesis of varying individual organic compounds. We will present the results of our material characterization using transmission electron microscopy and X-ray diffraction to determine average particle size and structure, nuclear magnetic resonance (NMR) to determine the organic groups protecting the nanoparticles and UV-Vis and photo-luminescence (PLS) spectroscopy. This work is supported by the Division of Materials Science, Office of Science, Basic Energy Sciences under contract DE-AC05-00OR22725 and the NSF under DMR-0412231.


PP9.11
A Comparative Study of AuCl2- and AuCl4- in the Galvanic Replacement Reaction with Ag Nanocubes. Leslie P Au, Xianmao Lu and Younan Xia; Biomedical Engineering, Washington University, St. Louis, Missouri.

The galvanic replacement reaction has proven to be a versatile method for preparing hollow and sometimes porous nanostructures. Here, we compare the galvanic replacement reactions between Ag nanocubes and different gold precursors: AuCl2- and AuCl4-. While both precursors gave nanostructures with hollow interiors, different morphological, compositional, and spectral evolutions were observed with the progressive addition of each gold precursor. When Ag nanocubes were reacted with AuCl4- solution, alloying and dealloying took place sequentially leading to the formation of nanoboxes and eventually nanocages. Alloying also occurs for the reaction with AuCl2-; however, the resultant nanoboxes exhibited thicker walls when compared to those obtained from the reaction with AuCl4-. Interestingly, no dealloying was observed for the reaction with AuCl2- even when excess precursor was added. This observation is probably due to differences in reaction stoichiometry: each AuCl4- reacts with three Ag atoms to generate one Au atom and two vacancies in the nanostructure, while AuCl2- reacts with Ag at a 1:1 ratio. This variation in reaction mechanism when using different gold precursors also resulted in different optical properties, with the position of the localized surface plasmon resonance being red-shifted to a smaller degree for AuCl2- than with the same amount of AuCl4-.


PP9.12
Tailoring the Optical and Catalytic Properties of Gold-Silver Nanoboxes and Nanocages by Introducing Palladium. Claire M Cobley1, Dean J Campbell2 and Younan Xia1; 1Biomedical Engineering, Washington University in St Louis, St Louis, Missouri; 2Chemistry and Biochemistry, Bradley University, Peoria, Illinois.

Nanoboxes and nanocages consisting of three noble metals - palladium, gold, and silver - were synthesized through the use of sequential galvanic replacement reactions between silver nanocubes and gold and palladium salts. These hollow structures displayed tunable surface plasmon resonance properties and could catalyze hydrogenation reactions such as the decolorization of methyl red dye. The surface plasmon resonance properties, composition, morphology, and catalytic ability were all affected by the order of addition of the metal precursors. If palladium precursor was added before gold precursor, the product was more porous, contained more palladium, had a further red-shifted SPR peak, and showed higher catalytic activity.


PP9.13
Synthesis of Bimetallic Nanostructures Based on Pd via a Galvanic Replacement Approach. Pedro Henrique Cury Camargo and Younan Xia; Biomedical Engineering, Washington University in St. Louis, St Louis, Missouri.

This work describes an investigation of the galvanic replacement reaction between well-defined Pd nanostructures (as sacrificial templates) and AuCl4- and PtCl62- ions. When single-crystalline Pd nanorods are reacted with AuCl4- ions, we found that the Au atoms resulting from the galvanic replacement reaction did not coat the entire surface of a Pd nanorod to generate a core-sheath or hollow nanostructure. In the earlier stages of the reaction, Au deposition was localized to both ends of a Pd nanorod. Then, a transition from two-end to one-end growth was observed, producing a new type of hybrid nanostructure in the tadpole shape consisting of a Au head and a Pd tail. Beyond this point, the Au served as nucleation sites for further Au deposition until the hybrid nanostructure was dismantled into round Au nanoparticles and smaller Pd fragments. When Pd single-crystalline nanocubes, nanobars and nano-octahedra were reacted with PtCl62- ions, a core-shell structure containing a hollow Pd core and dendrite-like Pt shells was formed. This study demonstrates that the utilization of Pd as sacrificial templates in galvanic replacement reactions with AuCl4- and PtCl62- ions enables the synthesis of Pd-Au and Pd-Pt bimetallic nanostructures with a variety of morphologies and shapes.


PP9.14
Structure and Ignition Properties of Nanoheaters Formed by Bimetallic Al-Ni Reactive Nanostructures. Qingzhou Cui1, Harshawardhan Jogdand2, Julie Chen2 and Zhiyong Gu1; 1Chemical Engineering, University of Massachusetts Lowell, Lowell, Massachusetts; 2Mechanical Engineering, University of Massachusetts Lowell, Lowell, Massachusetts.

A nanoscale heating source ("nanoheater") based on exothermic reaction between aluminum (Al) and nickel (Ni) is presented in this paper. Heating is one of the most efficient and frequently used methods to alter material geometry, structure, and properties in both ancient and modern industries. Traditional macro- and micro-scale heating methods such as resistance and infrared heating, which have played significant roles in materials processing and manufacturing, however, show limitations in handling nanostructures. With the continued miniaturization of electronics and devices, the expansion of multi-material systems, and the emergence of nanotechnologies, there is significant need for controlled and localized heating sources for thermal nanomanufacturing applications. There have been some methods under study to realize ultra-small heat spots with nanoscale dimensions, for example, nanoscale localized heating generated through a laser-heated AFM tip. However, most of the methods so far are serial, expensive, and difficult to scale-up. The formation process of Al and Ni alloys is a good candidate for heat-generation purposes due to its large exothermic reaction enthalpies. The fabrication and characterization of various types of nanoheater structures, e.g., bi-metallic nanowires and core-shell nanoparticles, are presented. These Ni-Al hetero- nanostructures are synthesized by electrochemical methods, either by electroplating or by electroless plating. The structures of bi-metallic nanoheaters are characterized by field emission scanning electron microscope (FESEM) and transmission electron microscope (TEM). Heat production from the alloy forming reaction is studied by differential scanning calorimetry (DSC). Upon ignition using different methods such as electrical, magnetic field, or laser heating, Ni-Al alloys are formed and one-time controlled and localized heat is generated from the exothermic reaction process. The ignition and heat propagation of alternating Al-Ni multilayered materials are studied by high-speed infrared (IR) camera. Preliminary studies show that multilayered Al-Ni nanostructures can be ignited by wired electrical spot touching. After ignition, the reaction self-propagates throughout a complex geometry, resulting in Al-Ni alloy phase. The heat production and propagation is also monitored by IR camera in a conductive copper media in which Al-Ni multilayered nanostructures are sandwiched in between, and theoretical modeling is performed to fit the experimental results. These new nanoheater sources, which can be either directly used in self-heating composite materials, dispersed in another material such as polymers or ceramics, or embedded within a MEMS/NEMS or microfluidic system, could revolutionize nanomanufacturing for miniaturizing devices and systems.


PP9.15
Abstract Withdrawn


PP9.16
Ellipsometry Characterization of Ag/amorphous Carbon Nanocomposite Thin Films. Zeuz Montiel, Oscar Garcia and Sandra E Rodil; Materia Condensada y Criogenia, Instituto de Investigaciones en Materiales-UNAM, México, D.F., Mexico.

Spectroscopic ellipsometry was used to determine the optical and structural properties of amorphous carbon (a-C)-silver thin films. The films were deposited by dc magnetron sputtering using the co-sputtering configuration where a small piece of Ag (less than 1%) was placed on top of a pure graphite target. The purpose was to obtain a nanocomposite structure, where the silver particles were nanometric and uniformly distributed in the carbon matrix. The deposition variables were power (40, 100 y 250 W) and target-substrate distance (4.0 x 10-2, 3.4 x 10-2 y 2.8 x 10-2 m), in addition to the rotation of the substrate. The conditions that lead to the Ag/a-C nanocomposites were the lowest power (40 W) and the shorter target-substrate distance (2.8 x 10-2 m). There were important differences between the ellispometric spectra when the structure of the nanocomposite was reached. This observation was supported on results of scanning electron microscopy (SEM) characterization. The theory of effective medium of Maxwell-Garnett was used to model the optical response of the nanocomposite films, where the matrix was modeled using Tauc-Lorentz and the Ag inclusions using a modification of the classical Drude - Lorentz dispersion functions. This allows the determination of the optical properties of the nanocomposito such as surface plasmon resonance, which might be of interest for applications. The analysis of the optical properties calculated from the model suggests an absorption process nearly to 3.5 eV for the nanocomposite film, which could be related to the surface plasmon resonance. Moreover, by comparing the different ellipsometric spectra for the films deposited under variable conditions and the results obtained by SEM it was possible to identify the nanocomposite structure only from the ellipsometric spectra.


PP9.17
Studies of Crystallinity of Nano-scale Pt on γ-Al2O3 by HRTEM and STEM. Long Li1, Sergio I Sanchez2, Joo H Kang2, Qi Wang3, Lin-lin Wang4, Zhongfan Zhang1, Duane D Johnson4, Anatoly I Frenkel3, Ralph G Nuzzo2 and Judith C Yang1; 1Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, Pennsylvania; 2Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois; 3Department of Physics, Yeshiva University, New York, New York; 4Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois.

Nano-scale Pt supported on γ-Al2O3 is widely applied in catalysts, fuel cells and sensors, etc. The surface chemistry depends intimately on the 3-dimensional atomic arrangement of the supported metallic nanoparticles (NPs) and the NP/support interactions. Pt NPs on γ-Al2O3 of a variety of sizes have been studied for the size-dependent crystallinity and the support effect, by high-resolution transmission electron microscopy (HRTEM) as well as high-angle annular dark-field (HAADF) of scanning transmission electron microscopy (STEM). Pt metallic NPs were synthesized through impregnating the Pt2+ precursor, Pt(NH3)4(OH)2 H2O, on γ-Al2O3, reducing in H2 gas at 673 K to remove the ligands and Pt NPs were prepared with 1 nm, 2 nm and 2.9 nm average sizes with loading of 1 wt%, 3 wt% and 5 wt%. Measurements of size and shape of Pt NPs were carried out with HAADF, and the crystallinity and the structural correlation to the crystalline γ-Al2O3 support were characterized by HRTEM, which provided both atomic structures of Pt NP and its support. It has been proved that the crystallinity of the Pt particles is size-dependent. The 1 nm Pt particles or smaller did not show clear evidence for crystallinity. The lack of uniform bond-lengths and order is supported by XAS and theoretical simulations. The Pt NPs (larger than 3 nm) showed f.c.c. structure, a = 0.39 nm, where some particles contained twin boundaries. The misorientation of the lattice of well crystalline Pt NPs with the support crystal lattice was frequently observed and with different misoriented angles. Meanwhile, HRTEM profile views showed that the Pt NPs were in contact with the γ-Al2O3 supports. These observations do not support the existence of a unique contact epitaxial relationship between nanoparticles and their crystalline support, and indicates a weak interaction (weak support effect) at the interface of Pt with its γ-Al2O3 support.


PP9.18
SPM Observation of Pt Nanoparticles Photodeposited on TiO2 (110). Suzumi Kataoka1,2, Takumi Hiasa1,2, Kenjiro Kimura1,2 and Hiroshi Onishi1,2; 1Department of Chemistry, Kobe University, Kobe, Hyogo, Japan; 2Advanced Measurement and Analysis, Japan Science and Technology, Kawaguchi, Japan.

Metal nanoparticles loaded on titanium dioxide is an industrially promising metal semiconductor system, owing to the photocatalytic capability of converting artificial pollutants to environmentally harmless compounds and of transforming water into H2 fuel. Among transition metals platinum is most widely used to activate the photocatalytic reactions on TiO2. Pt nanoparticles should be heterogeneous over the catalyst surface. It is important to know physical and chemical properties of individual Pt nanopartciles, whereas macroscopically averaged properties have been determined with conventional analytical methods. In our previous work [1], Pt nanoparticles were vacuum-deposited on a TiO2 (110) surface and observed with a Kelvin probe force microscope (KPFM). The work function of the deposited surface was locally determined particle-by-particle. In the current study, Pt nanoparticles are photodeposited on the TiO2 surface to simulate the preparation of real catalysts. The topography and electrostatic potential distribution are determined with the KPFM and compared with what observed on the vacuum-deposited nanoparticles. A single-crystalline (110) wafer of rutile TiO2 was calcined in air at 1273 K to show flat terraces and single-height steps. The calcined wafer was immersed in a methanol-water solution of H2PtCl6 and irradiated with UV light. Electrons photoexcited in the wafer reduce H2PtCl6 to Pt metal. The accompanying holes are consumed to oxidize methanol to formaldehyde. This wet process is commonly used to prepare Pt/TiO2 photocatalysts and also applicable metals other than Pt. The photodeposited wafers were washed, dried, and observed with a KPFM. The electrostatic potential is determined on individual Pt nanoparticles and related with the size and photodeposited site of the particles. It can be traced how the topography and electrostatic potential of individual nanoparticles respond to reactant adsorption, desorption, and UV light irradiation. The tip-surface force causes the resonance-frequency shift of the cantilever vibration. The highly sensitive detection of the force is enabled in the vacuum where the Q factor of the resonance vibration exceeds 1×104. The Q factor reduces in air by two orders of magnitude due to the viscous resistance. Ohta et al. [2] has recently developed a low-noise KPFM and achieved a single-nanometer resolution in air. Hence, in-situ observation in reactant vapor atmospheres is now possible. This leads to characterization of photocatalysts in working states. [1] A. Sasahara, C. L. Pang, H. Onishi J. Phys. Chem. B 110, 17584 (2006) [2] M. Ohta, K. Watanabe, R. Kokawa, K. Kobayashi, H. Yamada, A. Sasahara, H. Onishi, The 15th International Colloquium on Scanning Probe Microscopy, S4-33, 2007.


PP9.19
Abstract Withdrawn


PP9.20
The Functionalization of Electrospun Ceramic Nanofibers with Varying Noble Metals and Nanostructures for Green Catalysis. Eric Formo1, Eric Lee1, Zhenmeng Peng2, Mustafa Yavuz1, Xianmao Lu1, Hong Yang2 and Younan Xia1; 1Washington University, St Louis, Missouri; 2University of Rochester, Rochester, New York.

We have developed a simple procedure for derivation of the surface of anatase, and rutile TiO2 along with ZrO2 nanofiber membranes with Pt, Pd, and Rh nanoparticles and subsequently Pt nanowires. The fiber mats were then immersed in a polyol reduction bath to coat the surface of the fibers with Pt, Pd, and Rh nanoparticles of 2-5 nm respectively. Furthermore, the ceramic fibers decorated with Pt nanoparticles could serve as a scaffold upon which Pt nanowires of roughly 7 nm in diameter could be grown with lengths up to 125 nm. These decorated membranes, were then studied to ascertain their catalytic abilities in oxygen reduction and methanol oxidation reactions for fuel cell applications and their use as heterogeneous catalysis membranes for continuous flow organic synthesis.


PP9.21
Attaching Anisotropic Nanostructures of Noble Metals to ZnO and TiO2 Nanorods and Investigating the Mechanistic Details. Paromita Kundu and Ravishankar Narayanan; Materials Research Centre, Indian Institute of Science, Bangalore, India.

ZnO/metal and TiO2/metal nanohybrids are of immense importance in a variety of applications including visible-light catalysis. We present a route to attach noble metal nanostructures to ZnO and TiO2 nanorods using heterogeneous nucleation of precursor phases. The mechanism of formation of such nanohybrids is investigated in detail. Detailed characterization including high-resolution electron microscopy (HRTEM) and X-Ray Photoelectron Spectroscopy (XPS) has been carried out to understand the mechanism of formation of such hybrids. While conventional methods work for attaching nearly equiaxed nanostructures, the present method has been shown to be applicable for attaching anisotropic nanostructures.


PP9.22
Production of Metal Oxide Nanoparticles for Dye-Sensitized Solar Cells. Halil I Yavuz and Ahmet Macit Ozenbas; Metallurgical and Materials Eng., Middle East Technical University, Ankara, Turkey.

Dye-sensitized solar cells (DSSC) based on nanocrystalline inorganic oxides such as TiO2, ZnO and SnO2, are a relatively new class of low-cost solar cells. They are based on a semiconductor formed between a photo-sensitized anode and an electrolyte. A photo electrochemical system (PECS) extract electrical energy from light, including visible light. Dye-sensitized solar cells are extremely promising and currently attracting widespread interest for the conversion of sunlight into electricity because of their low cost and high efficiency and do not need elaborate apparatus to manufacture. For this purpose, nanopowders of metal oxides, TiO2, ZrO2 and Nb2O5 were synthesized by three different sol-gel methods. Comparison of nanopowders of metal oxides was done by investigating the structure of the nanoparticles and particle shape and size analysis. The results are listed below: 1. 3-4 nm ZrO2 particles were obtained by using Polymerizing Complexing Combustion (PCCM) method. 2. According to XRD results of TiO2 production methods, anatase TiO2 was obtained by using PCCM methods. 3. XRD studies showed that adding 5 % NbCl5 during PCCM process to obtain TiO2-5 % Nb2O5 mixed oxide did not change the structure of anatase-TiO2. 4. The addition of 5 % ZrO2 during PCCM process to obtain TiO2-5 % ZrO2 mixed oxide did not change the structure of anatase-TiO2. 5. According to SEM micrographs; 60-180 nm TiO2-50% ZrO2 particles were obtained using PCCM. 6. XRD spectrum of ZrO2 yielded the tetragonal structure of ZrO2.


PP9.23
Low Temperature Techniques to Induce Crystallinity in Anodically Formed Metal Oxide Nanotube Arrays. Nageh K Allam1, Thomas J LaTempa2, Karthik Shankar2 and Craig A Grimes1,2; 1MATERIALS Science and Engineering, Pennsylvania State University, University Park, Pennsylvania; 2Electrical Engineering, Pennsylvania State University, State College, Pennsylvania.

Valve metal oxides are versatile in their range of applications that include high-K dielectrics, gas sensing, biomedical implants, diffusion membranes, platforms for drug-eluting coatings, field emitters and photovoltaic cells. The electrochemical formation of valve-metal oxide nanotube arrays by anodization has significant advantages over other methods in that using relatively low temperatures and pressures it is possible to generate a vertically oriented self-organized ordered architecture. The currently used fabrication sequence forms amorphous nanotubes by anodization then employs a further heat-treatment step, typically greater than 350 C, to induce crystallinity. We report on a two-step electrochemical process to anodically form crystalline TiO2 nanotube arrays up to 1.4 μm in length at room temperature; a preformed crystalline oxide layer is electrochemically structured to produce the nanotubular architecture. The first step consists of treatment of Ti foil with H2O2 and/or ammonium persulfate containing electrolytes at 80°C followed by the second step of potentiostatic anodization in fluoride-containing media. Alternatively, we present a second crystallization technique that uses a low temperature oxygen plasma treatment to induce crystallinity in the initially amorphous nanotube arrays. The crystallinity of the architectures are confirmed via XRD and TEM measurements. The significance of this result is the achievement of compatibility of the titania nanotube architecture with flexible polymeric substrates as well as other temperature-sensitive substrates intended for semiconductor devices. Furthermore, since the nanotubes are crystalline immediately following anodization, subsequent treatment (including thermal annealing) could be employed to promote grain growth, reduce grain boundaries and enhance crystallinity. Low temperature crystallization allows reduction of the barrier layer in turn reducing recombination losses. Control of crystallinity is also important in dye-sensitized solar cells and photocatalysis where charge carrier transport improves with fewer grain boundaries, with the final goal of single crystalline nanotube arrays. The as-anodized crystalline nanotube arrays show good photocurrents and photoconversion efficiencies with their use as photoanodes per water photoelectrolysis. A liquid junction dye sensitized solar cell using the crystalline nanotube arrays is also demonstrated. References: N. K. Allam, K. Shankar and C. A. Grimes, Advanced Materials, accepted.


PP9.24
Transferred to PP7.4

PP9.25
Mechanism of Formation, Structure, and Biological Toxicology of Layered and Scrolled Amine-Templated Vanadium Oxides. Megan L. Roppolo1, Natalya A Chernova1, Shailesh Upreti1, M. Stanley Whittingham1 and Laura S Rhoads2; 1Chemistry and Materials, State University of New York at Binghamton, Binghamton, New York; 2Biology, State University of New York at Potsdam, Potsdam, New York.

The varied crystal chemistry of vanadium oxides, with oxidation states of 3+, 4+, and 5+, makes it possible for many interesting morphologies to be formed. For this reason, the formation of vanadium oxides is known to be very sensitive to synthesis conditions. In this work, sol-gel and hydrothermal reactions using a variety of synthesis conditions and starting materials produced a range of isostructural compounds with various morphologies including vanadium oxide nanotubes (VONTs) with several interlayer distances, vanadium oxide nano-urchins with a composition of VO2.3(C12H25NH3)0.4.0.3H2O, and the ethylene diamine-intercalated compound (enH2)V7O16. The structure of each of these compounds consists of V7O16 layers intercalated by amines (dodecylamine, hexadecylamine, ethylene diamine). V7O16 is a double layer of vanadium 4+/5+ octahedra with, presumably V4+, tetrahedra between the single sheets. These composite layered structures are scrolled in VONTs, the radial arrays of which are known as nano-urchins, and remain flat in (enH2)V7O16. Comparative analysis of the synthesis conditions, interlayer distances, degrees of amine protonation, vanadium oxidation states and particle morphologies of layered sol-gel precursors and final hydrothermal products has been performed to clarify the mechanism of structural curvature in VONT formation. Magnetic studies have indicated that non-scrolled compounds have a larger fraction of magnetic V4+ ions coupled by stronger antiferromagnetic exchange. Ion-exchange reactions of the products as well as additional vanadium oxide phases produced by varying pH in the synthesis of (enH2)V7O16 will be discussed. The cytotoxicity of the obtained products for biological systems, as measured through cell viability assays and microscopy, has indicated that nano-structured compounds may do more damage to the cells than their bulk analogs. This enhanced toxicity is most likely the result of physical interruptions of the cells with their surface attachments, rather than a biochemical disruption. This work is supported by the National Science Foundation through grant DMR-0705657.


PP9.26
Self-assembly of Zinc Carbonate Nanoparticles to Superstructures. Min Zhou, Department of Physics, Norwagian University of Science and Technology, Trondheim, Norway.

The fabrication of complex nano-architectures with controlled morphology, orientation, and dimensionality has been an active field of research due to the various potential applications of such architectures in different areas. Exploration of good synthetic methods for controlled construction of complex 3D architectures of functional materials via a chemical self-assembly route is an intensive and hot research topic.1-5 In this present work, we synthesized novel 3D zinc carbonate superstructures by a wet-chemical self-assembly method. zinc carbonate superstructures with various urchin-like structures have been synthesized via a simple polymer-mediated self-assembly process at room temperature, using ZnCl2 and NaHCO3 as reactants and appropriate Polymer as morphology controller. The zinc carbonate super-urchins which composed of nanorods and nanoparticles have been characterized by the SEM, TEM, and TGA. The superstructured zinc carbonate with well-defined shapes can be tuned by experimental parameters. SEM and TEM show the characteric morphologies of zinc carbonate and confirm their nanoparticles self-assembly behaviour forming urchins. We have used TGA to check the composition of the products. The present work suggests that tailoring an interaction between organic and inorganic molecules realizes a practical application of a self-assembly approach to the design and integration of functional nano- and micro-materials.


PP9.27
Preparation and Characterization of CeO2 Nanoparticles. Richard Hailstone1, A. G DiFrancesco1 and Kenneth J Reed2; 1Center for Imaging Science, Rochester Institute of Technology, Rochester, New York; 2Cerion Energy, Inc, Rochester, New York.

CeO2 nanoparticles have been prepared by an aqueous precipitation technique in which a cerium (III) salt is used to form Ce(OH)x by reaction with NH4OH. The crystalline product is converted to CeO2 by reaction with H2O2 or bubbling O2. To form a stable colloid, a stabilizer is also present in the reactor, typically an organic acid. Reaction byproducts are removed via diafiltration. Transmission electron microscopy (TEM) is used to image the nanoparticles and perform selected-area electron diffraction. For this study four nanoparticle sizes were used: 0.6, 2.2, 3.1, and 11.8 nm mean diameter, with coefficients of variation 15 to 25%. In all cases the selected-area electron diffraction patterns were consistent with that of CeO2, although the lattice constant increased with decreasing particle size, consistent with the lattice expansion. Our results are inconsistent with the proposal made by others that at very small size (<=1.5 nm) the cerium oxide adopts the C-type sesquioxide structure Ce2O3.


PP9.28
Assembly and Property of Vanadium Oxide Nanorod LB Film. Pengchao Zhang1, Liqiang Mai1,2, Yanhui Gu1, Chunhua Han1 and Lin Xu1; 1State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, School of Materials Science and Engineering, Wuhan University of Technology, Wuhan, Hubei, China; 2Department of Chemistry and Chemical Biology, Harvard University, Boston, Massachusetts.

One-dimensional (1D) nanostructure materials, which have excellent physical and chemical properties because of the shape anisotropy, have potential applications in nanoelectronics, nanooptoelectronics, ultra-density storage, scanning probe microscope, stealth material and so on. The self-assembly behavior under different solvents and substrates was investigated. (00l) crystal planes orientated and locally aligned VO2 nanorods films were assembled by Langmuir-Blodgett (LB) technique. The Langmuir film behavior was revealed based on the analysis of π-A curve, morphology and X-ray diffraction. Furthermore, the magnetism property study demonstrated that the LB film of VO2 nanorods is paramagnetism. ACKNOWLEDGEMENTS This work was supported by the National Nature Science Foundation of China (50672071, 50672072, 50702039), the Research Fund for the Doctoral Program of Higher Education (20070497012), Program for Changjiang Scholars and Innovative Research Team in University (PCSIRT, No. IRT0547), Ministry of Education, China, the Foundation for Innovation Research Team (2005ABC004) of Hubei Province. The authors are pleased to thank the strong support of Professor ZL Wang and Dr RS Yang of Georgia Institute of Technology.


PP9.29
Non-destructive Probing of the Chemical State of Buried TiOx Nanolayers. Beatrix Pollakowski1, Burkhard Beckhoff1, Falk Reinhardt1, Gerhard Ulm1, Stefan Braun2 and Peter Gawlitza2; 1Physikalisch-Technische Bundesanstalt, Berlin, Germany; 2Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.

Probing deeply buried nanolayers, photon-in photon out spectroscopy provides an approach to overcome some of the difficulties occurring when using non-destructive methods based on electron detection. Grazing incidence x-ray fluorescence in combination with near-edge x-ray absorption fine structure (GIXRF-NEXAFS) investigation enables a depth-resolving analysis of buried nanolayers with respect to both elemental composition and speciation. The GIXRF regime involves the strength of the x-ray standing waves (XSW) field at and below the surface which is, like the related mean penetration depth, dependent on both the incident angle and photon energy. Therefore, GIXRF has the specific advantage of high dynamics of the information depth from a few to several hundreds of nanometers. The sample system investigated first consists of several 10 nm titanium nanolayers oxidized to different extents and buried below 5 nm carbon layers. These layered structures were produced by means of ion beam sputtering deposition. For the investigation of this sample system, well-characterized monochromatic synchrotron radiation of the electron storage ring BESSY II and absolutely calibrated instrumentation was employed [1,2]. The results achieved so far confirm that GIXRF-NEXAFS has the potential to contribute substantially to the speciation of deeply buried nanolayers. In addition, appropriate angular corrections [3] based upon parallel XSW simulations can allow for a constant mean penetration depth, in particular, in the vicinity of absorption edges. The measured Ti-L3,2 absorption spectra exhibit different bonds and oxidation levels, e.g. TiO, Ti2O3 and TiO2 and the information is comparable to that from non-destructive electron-detection based methods when dealing with near-surface layers. References: [1] B. Beckhoff, J. Anal. At. Spectrom. 23 , 845 (2008) [2] B. Beckhoff et al., Anal. Chem. 79 , 7873 (2007) [3] B. Pollakowski et al., Phys. Rev. B 77 , 235408 (2008)


PP9.30
Reverse Diblock Copolymer Micelles used for the Synthesis of Inorganic Nanoparticles: Monitoring the Reaction Progress via Electron Microscopy and AFM. Taner Aytun1, Omer Faruk Mutaf1, Osman el-Atwani1, Vesna Srot2, Peter A van Aken2 and Cleva W. Ow-Yang1; 1Faculty of Engineering & Natural Sciences, Sabanci University, Istanbul, Turkey; 2Stuttgart Center for Electron Microscopy, Max-Planck-Institut fuer Metallforschung, Stuttgart, Germany.

Reverse diblock copolymer micelles have been widely used to synthesize nanoparticles of gold and sulfur-based inorganic compounds, using gas phase as the final processing step. We have used micelles of polystyrene-block-poly 2vinylpyridine (PS-b-P2VP) as reactor vessels to engender the precipitation of ZnO nanoparticles. In contrast to pre-existing approaches, ours enables further manipulation of the loaded, but still intact, micelles for controlled assembly schemes. To monitor the progress of reaction inside the micelle reactors, we took advantage of the contrast in mechanical properties and in atomic number of the micelle corona and inorganics-loaded core. By choosing tapping mode AFM conditions such that energy was dissipated during the tip-sample interaction, the variation in elastic properties were correlated with the phase shift of the oscillating cantilever and mapped in the phase images. High angle annular dark field imaging and chemical spectroscopy in a dedicated scanning transmission electron microscope revealed the distribution of the cation reactants in the micelle core. These two characterization techniques offer additional means for elucidating the synthesis of inorganic materials in polymeric micelle reactors.


PP9.31
A Combined Computational - Experimental Study on the Adsorption of Probe Molecules on ZnO Nanorods. Ozlem Ozcan1, Alexander T Blumenau1 and Guido Grundmeier2; 1Interface Chemistry and Surface Engineering, Max Planck Institut für Eisenforschung, Düsseldorf, Germany; 2Department of Technical and Macromolecular Chemistry, University of Paderborn, Paderborn, Germany.

ZnO is widely studied in the literature due to its great technological importance. Recently, the synthesis of various geometries of nanostructures was realized by a number of groups. The substrate independent growth of single crystalline nanorod films with c-axis orientation opens up new opportunities in application of the techniques available for amorphous or polycrystalline materials, to more defined single crystalline substrates. Moreover, the tuneable size of nanorods down 10nm narrows the dimension gap between computational and experimental conditions. In this study, we first aimed at understanding the mechanism of growth of ZnO nanorods and to link the preferential c-axis orientation to the stability of surfaces. DFT Calculations were performed on all low index surfaces and furthermore the polar surfaces were analysed with various configurations of adsorbates for possible stabilization mechanisms. The adsorption energies of small probe molecules like H2O and CO were calculated on those surfaces. Rods periodic in c-direction were generated with different diameters and diffusion barriers for Zn atoms among the rod edges were evaluated. The DFT calculations were done with SIESTA Molecular Dynamics Package. In the experimental part of the study the aim was to prepare nanorod films with different diameters and thereby different ratio of crystallographic surfaces. Highly oriented ZnO nanorod films were prepared using hydrothermal methods on polished Zn, Si and Au coated Si substrates and also on ZnS ATR (Attenuated Total Reflection) crystals. Their crystallograpic orientation was determined using X-Ray Diffraction and Scanning Electron Microscopy (SEM) was used in studying their morphology. The adsorption of H20/D20 on ZnO nanorod films was monitored in situ with ATR spectroscopy and Quartz Crystal Microbalance (QCM) measurements. The desorption energies of H2O/D2O and CO were measured using Temperature Programmed Desorption (TPD). Computational results will be presented with related experimental data and possible technological highlights especially in the field of corrosion science will be discussed in the presentation.


PP9.32
Thermodynamic Stability and Electronic Structure of LaMnO3 and La0.875Sr0.125MnO3 (001) Surfaces: First-principles Calculations by Means of a Hybrid Density-functional Theory. Sergej Piskunov1,3,4, Eckhard Spohr4, Timo Jacob5, Eugene Heifets6, Eugene Kotomin1,3 and Donald Ellis2,3; 1Inst. of Solid State Physics, University of Latvia, Riga, Latvia; 2Dept. Physics & Astronomy, Northwestern University, Evanston, Illinois; 3Materials Research Center, Northwestern University, Evanston, Illinois; 4Dept. of Theoretical Chemistry, Univ. of Duisburg-Essen, Essen, Germany; 5Dept. of Electrochemistry, University of Ulm, Ulm, Germany; 6Max Planck Institute for Solid State Research, Stuttgart, Germany.

LaMnO3 and La1-xSrxMnO3 (LSM) are extensively studied perovskite-type oxides because of their outstanding magnetic and electronical properties, such as colossal magneto- resistance, half-metallic character, and composition- dependent metal-insulator transition. In particular, understanding of the mechanism of reaction of oxygen reduction at the surfaces of LSM nanofilms deposited on oxide electrolytes demands theoretical analysis at the atomistic level. In the present work, first-principles calculations by means of a hybrid density-functional theory are used to describe La(Sr)O- and MnO2-terminated surfaces of both cubic LaMnO3 and LSM. Calculated surface cleavage energies suggest that (001) faces would predominate among low index surfaces. The effects of oxygen defects, critical for ionic conduction in LSM cathodes, are examined and thermodynamic stability diagrams are obtained.


 

SESSION PP10: Porous and Framework Materials
Chairs: Stephanie Brock and Yadong Yin
Thursday Morning, December 4, 2008
Back Bay C (Sheraton)


8:30 AM *PP10.1
Spontaneously Formed Porous and Composite Nanostructures. Daniel Shoemaker1, Eric S Toberer3 and Ram Seshadri1,2; 1Materials, University of California, Santa Barbara, California; 2Chemistry & Biochemistry, University of California, Santa Barbara, California; 3Materials Science, Caltech, Pasadena, California.

Solid-solid and solid gas reactions can give rise to interesting micro and nanostructures that can be engineered to serve a number of useful functions. We describe an extensive body of work on engendering porosity (micro, meso, and hierarchies) in functional solids through spontaneous processes, without the use of pre-formed templates. Carried out in epitaxial thin films, the resulting connected pores can be aligned through the appropriate selection of the specific orientation of the substrate single crystal. This work has led to the exploitation of magnetic interfaces that can be formed through solid state reactions, including exchange-biased nanostructures of metals on antiferromagnetic monoliths.


9:00 AM PP10.2
Periodic Mesoporous Organosilicas with Domain Functionality: Synthesis and Advanced Characterization. James Jones, Colin Wood and Yaroslav Khimyak; Chemistry, University of Liverpool, Liverpool, Merseyside, United Kingdom.

Since the first synthesis of ordered periodic mesoporous organosilicas (PMO) in 1999 [1] much research effort has been placed into both development and understanding the mechanism of their formation. The methodology towards multifunctional PMOs possessing two or more functionalities incorporated into the pore walls has been developed [2, 3]. However, the ability to direct and control the location and distribution of the organic functionalities has proven challenging. In this work we present a novel synthesis of bifunctional PMO via tri-block co-polymer and cationic templating leading to materials with domain distribution of different functional groups in the framework. The ability to direct the distribution of functional groups in the products has been achieved by using a controlled pre-hydrolysis of silica sources prior to their addition to the solution of template [4]. The mesoscopic ordering of such solids is proven by powder X-ray diffraction and nitrogen adsorption measurements. Use of aromatic bridged organosilane precursors resulted in the formation of PMO with mixed crystalline and amorphous domains. Solid-state NMR is a method of choice for characterization of the molecular structure of such complex materials exhibiting both structural and dynamic heterogeneities. Advanced solid-state NMR methods enabled us to prove the composition of the hybrids and to assess motional differences dependent on the location of the organic functionalities within the porous structure [4]. 2D NMR methods (1H-29Si HETCOR, 1H-1H correlation, fast MAS NOESY etc.) were essential to probe the local organisation and spatial proximity of different functional groups thus serving as a diagnostic tool for chosen synthetic strategy. [1]. S. Inagaki, S. Guan, Y. Fukushima, T. Ohsuna, and O. Terasaki, J. Amer. Chem. Soc., 1999, 121, 9611. [2]. T. Asefa, M. Kruk, M. J. MacLachlan, N. Coombs, H. Grondey, M. Jaroniec, and G. A. Ozin, J. Amer. Chem. Soc., 2001, 123, 8520. [3]. B. J. Hughes, J. B. Guilbaud, M. Allix, Y. Z. Khimyak, J. Mater. Chem., 2005, 15, 4728. [4]. J. T. A. Jones, C. D. Wood, C. Dickinson and Y. Z. Khimyak, Chem. Mater., 2008, 20, 3385-3397.


9:15 AM PP10.3
High Temperature Behavior of CO2 Selective Nanoporous Silica Membranes. Vidya Ramaswamy, James A Ruud, Patrick D Willson and Anthony Y Ku; GE Global Research, Niskayuna, New York.

Porous inorganic membranes have the potential to enable higher efficiency gas separations because of their thermal and chemical stability and mechanical strength. While gas separation in porous membranes typically takes place by the removal of the smaller or lighter molecule from the gas stream, selective adsorption and surface diffusion of the heavier molecule can result in reverse selective membranes. Membranes exhibiting high temperature reverse selectivity may be utilized in applications requiring selective removal of the heavier molecule, such as the removal of CO2 from a syngas process stream. Nanoporous sol-gel derived silica membranes exhibit substantial selectivity for the flow of CO2 over H2 at room temperature, most likely due to surface diffusion of CO2 along the pore walls. Our measurements of the gas permeation and separation characteristics of these membranes as a function of temperature show that with increasing temperature, there is a decline in the CO2 selectivity of these membranes. This is due to both a decrease in CO2 flux and an increase in H2 flux. The measured CO2 flux is consistent with a decrease in the surface diffusive component of CO2 flux, which in turn is due to a reduction in the amount of adsorbed CO2 with increasing temperature. Adsorbed CO2 can also lead to a decrease in the effective pore size. The increase in H2 transport with temperature is due to a reduction in pore blocking, caused by CO2 desorption. We estimate the surface concentration and diffusivity of CO2 on silica from measurements of CO2 adsorption isotherms. We have developed a transport model for CO2 selectivity with only one free parameter, the effective pore radius. The model takes into account the surface diffusion of CO2, Knudsen diffusion of CO2 and H2, and CO2 pore blocking, and is in good agreement with the observed transport behavior. Based on insights from silica membranes, guidelines for pore sizes and pore wall compositions are established to enable systematic development of membrane materials with high temperature CO2 selectivity. Acknowledgement This material is based upon work that was supported by the U.S. Department of Energy under award number DE-FC26-05NT42451.


9:30 AM PP10.4
Silicophosphate Mesoporous Derivatives: Aerosol Assisted Synthesis Solid State NMR Methodology for New Insights in Chemical and Spatial Connectivities! Christian Bonhomme, Cristina Coelho, Thierry Azais, Laure Bonhomme, Cedric Boissiere, Clement Sanchez and Florence Babonneau; universite P et M Curie, Paris, France.

Silicophosphate materials are of prime importance in the frame of biocompatible materials. Porosity is also a key parameter which will orient the performance of a given material. Silicophosphate nanoparticles exhibiting high phosphorus content were synthesized by aerosol assisted methods [1]. To the best of our knowledge, such derivatives correspond to the first Si-O-P mesoporous materials. Mesoporosity was clearly demonstrated by XRD and imaging techniques and full chemical analysis was performed by EDS. Solid state NMR offers unique perspectives for the fine description of connectivities within the mesoporous materials. Such connectivities can be related to chemical bonding or spatial interaction, depending on the nature of the involved interfaces. The chemist can manipulate several interactions, such as the dipolar interaction (spatial in nature) or the J coupling interaction (through-bond interaction). The detailed study of the Si-O-P mesoporous materials will allow us to propose a general solid state NMR approach, which can be potentially extended to all interface bearing materials. For that purpose, the latest developments in 1H high resolution solid state NMR and triple resonance experiments 1H-X-Y will be presented. Special emphasis will be made on the 31P/29Si spin pair which is of paramount importance in the frame of potential biomaterials [3,4]. At a molecular level, the fine description of the obtained materials was achieved by 31P/29Si CP MAS experiments at low temperature (-30°C). Spatial connectivities between 29Si and 31P nuclei were established through dipolar interaction [2]. Biocompatibility and bioactivitity of these new materials are currently studied. [1] Y. Lu et al., Nature, 398, 223 (1999). [2] C. Bonhomme et al., Acc. Chem. Res., 40, 738 (2007). [3] C. Coelho et al. J. Magn. Reson. 187, 131 (2007) [4] C. Coelho et al., Inorg. Chem. 46, 1379 (2007)


9:45 AM PP10.5
Abstract Withdrawn



10:30 AM PP10.6
Acid-Base Interactions and Enthalpies of Formation of Cobalt and Zinc Phosphate Framework Materials. Alexandra Navrotsky and So-Nhu Le; UC Davis, Davis, California.

Cobalt and zinc form many phosphates, some of which for open zeolite-like structures. Alkali and ammonium cobalt and zinc phosphates show extensive polymorphism. Thermal behavior, relative stabilities, and enthalpies of formation of NaCoPO4, KCoPO4, RbCoPO4, NH4CoPO4, and NH4ZnPO4 polymorphs have been studied by differential scanning calorimetry, high-temperature oxide melt solution calorimetry, and acid solution calorimetry. The extensive polymorphism is consistent with small enthalpies of transition among polymorphs. There is a strong relationship between enthalpy of formation from oxides and acid - base interaction for cobalt and zinc phosphates and also for aluminosilicates with related frameworks. Cobalt and zinc phosphates exhibit similar patterns of enthalpies of formation as aluminosilicates, but their enthalpies of formation from oxides are more exothermic because of stronger acid - base interactions. Enthalpies of formation from ammonia and oxides of NH4CoPO4 and NH4ZnPO4 are similar, reflecting the similar basicity of CoO and ZnO. The use of acid/base scales rather than ionic potential to compare the effect of different cations, including NH4+, on heat of formation is discussed


10:45 AM PP10.7
Organically-functionalised Supertetrahedra as Building Blocks for Hybrid Materials. Paz Vaqueiro and M Lucia Romero; Chemistry, Heriot-Watt University, Edinburgh, United Kingdom.

Metal-sulfide supertetrahedral clusters have been increasingly used as building blocks for the preparation of wholly inorganic three-dimensional frameworks. However, as a result of the lack of flexibility of the metal-sulphur-metal angle, only a small number of structural types have been obtained to date. In order to obtain new three-dimensional frameworks, it is necessary to devise alternative ways of linking the clusters. Whilst in solvothermally-prepared metal chalcogenides containing the main group elements In, Ge, Sn, As and Sb the template molecules generally enter the structure through weak hydrogen bonding, we have recently found that in the Ga-S system, covalent bonding between the metal and the amine molecules is possible.[1] We have exploited the ability of gallium to form covalent bonds with amines under solvothermal conditions, to prepare organically-functionalised supertetrahedra,[2] and we present here our initial results on the synthesis and characterisation of novel hybrid materials containing organically-functionalised supertetrahedra, in which polydentate ligands act as linkages between gallium-sulfide supertetrahedral clusters. A number of materials containing isolated clusters or dimers in which two supertetrahedral clusters are linked through a bitopic ligand, will be described. In addition, by using bipyridyl linkers, we have succeeded in the synthesis of one- and two-dimensional extended structures. Hybrid chains in which bipyridyl molecules and supertetrahedral clusters alternate will be presented, as well as layered materials containing corrugated honeycomb-like layers. References: 1. P. Vaqueiro, Inorg. Chem., 45, 4150 (2006). 2. P. Vaqueiro and M. L. Romero, Chem. Commun., 3282 (2007).


11:00 AM PP10.8
Flexible MOFs : What Are They Good For? Christian Serre and Gerard Ferey; University of Versailles, CNRS, Versailles, France.

Porous hybrid solids are fascinating solids,[1-3] due to their potential applications in catalysis, separation, storage, adsorption or drug delivery. If most Metal Organic frameworks (MOFs) exhibit a rigid framework, a few of them possess an unusual behavior with a large flexibility of their structure, with changes in cell volumes depending on their pore content.[2] Our group has reported two types of flexible MOFs built either on chains of metal octahedra, i.e. the metal terephthalates MIL-53(Al, Cr, Fe) (MIL: Material Institut Lavoisier),[4] or made from trimeric inorganic sub-units, i.e. the series of iron(III) or chromium(III) MOFs denoted MIL-88A, B, C and D constructed from different dicarboxylate linkers.[5] The MIL-53 solids breathe upon hydration-dehydration with a variation in cell volume around 40 % while the MIL-88 solids exhibit a giant and reversible swelling effect with an increase of 85 % (MIL-88A) up to 220 % (MIL-88D) in their cell volumes.[6] Adsorption experiments of green house gases, polar or apolar vapours and liquids have been performed using these solids.[7-9] In most cases, in situ XRPD or Infra-red spectroscopy experiments have been conducted to analyse the breathing behavior of the flexible solids upon adsorption of guest molecules. Results suggest that the breathing phenomenom occurs in most cases with a rather selective behavior and that selectivity depends not only on the structure and the organic linker but also on the nature of the metal present in the nanoporous hybrid solid. These results pave the way for new applications in the field of adsorption. References [1] G. Férey, Chem Soc Rev, 37, (2008), 191. [2] S. Kitagawa, R. Kitaura, S.-I. Noro, Angew. Chem. Int. Ed, 43(2004) 2334. [3] H. Li, M. Eddaoudi, M.O’Keeffe, O.M. Yaghi, Nature 402, (1999) 276. [4] (a) C. Serre, F. Millange, C. Thouvenot, M. Nogues, G. Marsolier, D. Loüer, G. Férey J. Am. Chem. Soc., 124 (2002), 13519; (b) T. Loiseau, C. Serre, C. Huguenard, G. Fink, F. Taulelle, M. Henry, T. Bataille and G. Férey : Chemistry, a European Journal, 10 (2004) 1 [5] (a) C.Serre, F. Millange, S. Surblé, G. Férey Angew. Chem. Int. Ed. 43, (2004), 6286; (b) S.Surblé, C.Serre, C. Mellot-Draznieks, F. Millange, G. Férey, Chem Comm. (2006) 284. [6] (a) C.Mellot-Draznieks, C. Serre, S. Surblé, N. Audebrand, G. Férey J. Am. Chem. Soc. 127, (2005), 16273; (b) C. Serre, C. Mellot-Draznieks, S. Surblé, N. Audebrand Y. Filinchuk, G. Férey, Science, 315, (2007) 1828 [7] C. Serre, S. Bourrelly, A. Vimont, N. Ramsahye, G. Maurin , P.L. Llewellyn, M. Daturi, Y. Filinchuk, O. Leynaud, P. Barnes, G. Férey, Adv. Mater. 19 (2007), 2246 [8] T. K. Trung, P. Trens, N. Tanchoux, S. Bourrelly, P. L. Llewellyn, S. Loera-Serna , C. Serre, T. Loiseau, F. Fajula and G. Férey, submitted (2008) [9] F. Millange, C. Serre, N. Guillou, G. Férey, R. I. Walton, Angew Chem. Int Ed., 47, (2008), 4100


11:15 AM PP10.9
Guest-dependent High Pressure Phenomena in a Nanoporous Metal-Organic Framework Material. Karena W Chapman1, Gregory J Halder2 and Peter J Chupas1; 1X-ray Science Division, Argonne National Laboratory, Argonne, Illinois; 2Materials Science Division, Argonne National Laboratory, Argonne, Illinois.

The structural and chemical diversity of metal-organic framework materials (MOFs) underlies widely acknowledged potential applications including in gas storage and separation. The elaborate topologies of MOFs are likely to be associated with a greater variety of pressure-induced phenomena than the geologically-relevant minerals commonly studied at elevated pressure. Thus far, the structural characterization of MOFs has been exclusively limited to near atmospheric pressures, however, many of the envisioned real-world applications are likely to involve significantly higher pressure environments. For example, densification of MOF samples to optimize volumetric gas storage capacities through compression up to several GPa may induce distortions of the framework and pore structure, and accordingly may significantly alter the gas sorption properties. As such, understanding of the impact of pressure on porous MOFs is not only of immense fundamental interest, it is also relevant to many of the applications for which these materials are being considered. Here we present the results of structural studies of a nanoporous MOF at high pressure using synchrotron powder diffraction.


11:30 AM PP10.10
Strategies for the Synthesis of Zeolite-Templated Carbons with High Hydrogen Storage Capacity. Yongde Xia2, Walker Gavin2 and Robert Mokaya1; 1School of Chemistry, University of Nottingham, Nottingham, United Kingdom; 2Division of Materials Engineering and Materials Design, University of Nottingham, Nottingham, United Kingdom.

Porous carbons with well-ordered pore systems are potentially useful as gas storage materials. Porous carbon materials with ordered pore channels may be obtained via the template carbonization method, which involves the introduction of suitable carbon precursors into the pores of a hard template followed by carbonization and finally removal of the template. A variety of inorganic templates including microporous zeolites and mesoporous silicas may be used to prepare porous carbons. Zeolites have been used as templates because of their attractive three-dimensional channels and well-defined nanospace that offer a route to highly microporous carbons. This work explored strategies for the synthesis of high surface area carbon materials that utilize zeolites as templates. We have not only assessed the performance of a number of zeolites as templates, but also investigated the use of liquid impregnation or chemical vapour deposition (CVD) singly or in combination. A variety of carbon precursors have been used to generate carbons with optimised textural properties and enhanced hydrogen storage capacity. The structural ordering of the carbon materials is indicated by powder XRD patterns that exhibit up to three well resolved diffraction peaks. The carbons possess high surface area of up to 3700 m2/g and pore volume of ca. 2 cm3/g. A high proportion of the porosity in the carbons is from micropores; the micropores exhibit a narrow size distribution. The carbons exhibit enhanced hydrogen storage capacity that is typically above 6.0 wt% at 77 K and 20 bar.


11:45 AM PP10.11
New Bialkali AlH_6-based Alanates for Hydrogen Storage Predicted using Prototype Electrostatic Ground States (PEGS). Eric Majzoub1 and Vidvuds Ozolins2; 1Physics, University of Missouri, St. Louis, St. Louis, Missouri; 2Materials Science and Engineering, UCLA, Los Angeles, California.

Hydrogen storage materials composed of complex anions such as (AlH4)-, (AlH6)3-, and (BH4)-, are at the forefront of research for on-board vehicular applications. The optimial PEM (proton exchange membrane) fuel cell temperature range for utilization of waste heat requires the storage medium to release hydrogen below 100C. The stability of complex anionic hydrides is very sensitive to ionic radii, and these materials generally do not support continuous alloying as is common with interstitial hydrides. One strategy to find new materials is to theoretically screen new (unreported/undiscovered) stoichiometric compounds for thermodynamic stability. We present the first absorption and desorption data obtained from new bialkali alanate storage materials predicted using a theoretical method of crystal structure searching in complex anionic materials. We will briefly describe the theoretical method based on prototype electrostatic ground states (PEGS), and demonstrate a few predicted AlH6-based alanate materials that indeed show reversible hydrogen sorption.


 

SESSION PP11: Thermoelectrics and Spintronics
Chair: Ram Seshadri
Thursday Afternoon, December 4, 2008
Back Bay C (Sheraton)


1:30 PM *PP11.1
New Nanostructured Solids with Unprecedented Properties. David Johnson, Chemistry Department and Materials Science institute, University of Oregon, Eugene, Oregon.

We have developed a synthetic approach to new materials that uses composition control on an Angstrom length scale to control solid-state reaction pathways, leading to the self-assembly of new nanostructured compound by avoiding compounds on equilibrium phase diagrams. One class of new compounds we are currently investigating consists of two or more compounds that are interleaved layer by layer with unit cell control of the thickness of the constituent compounds. Crystalline superlattices with as many as 130 (00l) diffraction lines have been prepared within this class of materials. The ability to interweave structures on a nanometer length scale permits us to explore the effects of charge transfer and bonding changes at the interfaces on physical properties. Exceptionally low lattice thermal conductivities have been discovered for this class of materials. The anisotropic nature of the structure of and the disorder in these new compounds and the variation of both electrical and thermal properties with nanostructure will be discussed. We believe the ability to prepare entire families of new nanostructured compounds permits a new "thin film metallurgy" or “nanochemistry” in which nanostructure and composition can both be used to tailor physical properties.


2:00 PM PP11.2
Silicon and Germanium Network Polyhedra: Relationship between Motions of Endohedral Atoms and Framework Lattice. Katsumi Tanigaki1, Jun Tang1, Kazumi Sato1, Masatoshi Watahiki1 and Alfonso S Miguel2; 1WPI and Department of Physics, Tohoku University, Sendai, Japan; 2Laboratoire de Physique de la Matière Condensée et Nanostructures, University Lyon 1 and CNRS, Lyon, France.

When the special conditions are constrained during the formation in solids consisting of IVth group of elements like silicon, germanium and tin, nano materials having network polyhedra are produced. Although the sp3-hybridized bonding is favored in silicon and germanium different from carbon where both sp2- and sp3- hybridization are realized in graphite and diamond, a new series of materials featured by the polyhedral frameworks, so called clathrates, form. In these nano materials, one of the intriguing issues is phonons. Because of their accommodation spaces inside, the phonons different from the conventional lattice phonons should be taken into account. For instance, intra-cluster phonons are believed to play an important role for giving rise to unique electronic states and anharmonic oscillations with little dispersions of endohedral atoms are also expected to provide exotic interactions with lattice phonons as well as conduction electrons at the Fermi surface. Such phonons have recently been drawing much attention in materials science and are called as rattling phonons. In this meeting, we would like to present our recent systematic experimental studies on silicon and germanium clathrates [1-4] with emphasis on superconductivity, energetics of endohedral atoms observed by soft X-ray spectroscopy and the phonons monitored by specific heat measurements. We show possibility that the framework structure consisting of III -IV elements sensitively changes depending on the type of endohedral atoms (Sr or Ba) in the case of Ga16(Si,Ge)30 framework. On the other hand, a different situation can be seen for homogeneous framework clathrates such as Si46, Si100 and Ge100, because energetic stabilization can only be obtained by Jahn Teller distortion or displacement of endohedral atoms. We will provide experimental evidences to demonstrate such remarkable differences. This gives reasonable understanding on the physical properties of superconductivity as well as electronic phase transition so far observed in these clathrates families. The present work is supported by Grand-in-Aid for Science Research from the Ministry of Education, Culture, Sports, Science and Technology of Japan (No. 15201019, 18204030, 18651075 and 19014001) as well as by Tohoku University GCOE program “Particle Matter Hierarchy” MEXT Japan and Center for Interdisciplinary Research Project in Tohoku University. [1] K. Tanigaki, et al, Nature Materials, 2, 653 (2004). [2] T. Rachi, K. Tanigaki, R. Kumashiro, J. Winter, H. Kuzmany, Chem. Phys. Letters, 409, 48 (2005). [3] T. Rachi, K. Tanigaki et al., Phys. Rev. B, 72, 144504 (2005). [4] Takeshi Rachi , Katsumi Tanigaki et al., J. Physics and Chemistry of Solids 67, 1334-1337 (2006).


2:15 PM PP11.3
Thermoelectric Properties of Ternary Zinc Antimonides. Eric S Toberer1, Andrew F May1, Cidney J Scanlon1, Brent C Melot2 and Jeffrey Snyder1; 1Materials, California Institute of Technology, Pasadena, California; 2Materials, University of California, Santa Barbara, Santa Barbara, California.

Zintl phases have recently been identified as a promising class of materials for thermoelectric applications, with several compounds exhibiting a figure of merit (zT) in excess of unity. Given the vast number of known Zintl compounds, there is a need to establish structure-property trends for the selection and design of thermoelectric materials. This work focuses on ternary Zintl compounds based on zinc antimonide such as LiZnSb, KZnSb, XZn2Sb2 (X = Sr, Ca, Yb), and SrZnSb2. Measurements of the thermoelectric properties (Seebeck coefficient, electrical conductivity, Hall coefficient, thermal conductivity) are conducted to high temperature. This complete picture of the transport properties allows a comparison to band structure calculations (Madsen, JACS 2006) which predict high zT values for these antimonides.


2:30 PM PP11.4
Crystal Chemistry and Thermoelectric Properties of New Mixed Valent Rhodium Oxides with Channel Structures. Hiroshi Mizoguchi1, Tosapal Maluangnont1, Lev N Zakharov1, Arthur P Ramirez2, Arthur W Sleight1 and Mas Subramanian1; 1Department of Chemistry, Oregon State University, Corvallis, Oregon; 2Bell Laboratories, Alcatel-Lucent, Murray Hill, New Jersey.

Many complex manganese oxides crystallize in rutile related octahedral network structures with large channels. The octahedral cation (M ion) has to be reduced moderately from 4+ in order to stabilize the structure by the electrostatic columbic force between host and guest, that is, (MO2)A. The valence of Mn ion in oxides is changeable from +2 to +4 and low temperature processes, such as hydrothermal reaction, are often used for the synthesis due to valence instability. On the other hand, Rh ion with 4d electrons often takes 3+ and 4+ valence states and can be synthesized at temperatures in air readily. Beside, it prefers only octahedral coordination and will occupy framework-site selectively. These characteristics made us consider mixed valent Rh oxides as one of the potential candidates for designing materials with large channels. In this paper we report on the synthesis, crystal growth and structural characterization of several new rhodium mixed valent oxides. Single crystals of (Bi6O5)Rh12O24 with todorokite-type (3x3 octahedral channel)were grown and partial charge ordering between Rh3+ and Rh4+ has been confirmed by crystal structure refinements. We also reports the synthesis of several new Rh oxides with tunnel structures, such as (Ln, Bi)2/3-yRh2O4 with CaFe2O4-type and AA’2Rh6O12 which takes same structure as SrCa2Sc6O12. In these oxides, the valence of Rh is about +3.1 - +3.4, showing the metallic or degenerate semiconductor behavior due to the positive hole located in the valence band composed from Rh4d-O2p orbitals (t2g* band). The large Seebeck coefficient coupled with the high electrical conductivity indicates that many of these Rh oxides may be promising thermoelectric materials for power generation. The observed thermoelectric properties will compared to mixed valent Co oxides and essential ingredients for the enhanced thermoelectric power and high conductivity due to spin and orbital degrees of freedom of Rh3+/Rh4+ in the low spin state will be discussed.


2:45 PM PP11.5
Densities of States in Boron Substituted Kekule and Non-Kekule Structured Nanocarbon Ensembles. Dieter M Gruen, Larry A. Curtiss and Paul C Redfern; Materials Science Division, Argonne National Laboratory, Argonne, Illinois.

The recent finding that boron doped nanocarbon ensembles (NCE's) display thermoelectric power factors that are enhanced 30-40 fold at 700C over undoped NCE's was ascribed to the creation of a multiplicity of electronic states within a narrow energy band around the Fermi level leading to an increase in configurational electronic entropy.(1) In the present work, we present detailed DFT calculations to support this supposition. The calculations are based on a model for the NCE's involving a stack of four graphene sheets containing each containing 70-96 carbon atoms. Boron doping is modeled by replacing two of the carbons with boron atoms situated in different positions relative to each other in each of the four sheets. In all, five electronically distinct particle entities were treated in our calculations, each displaying a characteristic distribution of electronic states. High densities of states are found in a very narrow energy region 0.1 eV above and below the Fermi level. A detailed examination of the density of states in this important energy regime reveals that the distribution of states depends not only on the boron configurations within the sheets but also on sheet geometry. It turns out that sheet geometries determine whether or not a particular graphene sheet can or cannot have a Kekule structure. In non-Kekule structures, high spin densities can occur. In particular, for such situations, ground states with multiplicities higher than singlet are sometimes found. The physical basis for the subleties of the interplay of sheet geometry and boron configurations on the densities of states near the Fermi level will be discussed and the relationship of electronic structure to thermoelectric properties will be highlighted. (1)D. M. Gruen, P. Bruno, M. Xie, "Configurational, electronic entropies and the thermoelectric properties of nanocarbon ensembles", Appl. Phys. Lett., 92, 143118, (2008) This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, at Argonne National Laboratory, an U.S. Department of Energy Office of Science laboratory, operated by UChicago Argonne, LLC, under contract DE-AC02-06CH11357


3:30 PM *PP11.6
Multifunctional Heusler compounds: New Properties. Felser Claudia1, Joachim Barth1, Fred Casper1, Jürgen Winterlik1, Catherine A Jenkins2, Gerhard H Fecher1, Ramamoorthy Ramesh2 and Benjamin Balke1; 1Institute of Inorganic Chemistry, University of Mainz, Mainz, Germany; 2Department of Materials Science and Engineering,, UC Berkeley, Berkeley, California.

The development of magnetic Heusler compounds specifically designed as materials for spintronic applications has made tremendous progress in the very recent past [1]. Heusler compounds can be made as half-metals, showing a high spin polarization of the conduction electrons of up to 100% [2]. High Curie temperatures were found in Co2-Heusler compounds with values up to 1120 K in Co2FeSi [3]. Ferrimagnetic Heusler compounds are candidates for spin torque application, because of their low magnetic moments despite their high Curie temperatures. Mn3Ga with Heusler structure was predicted to be a half metallic compensated ferrimagnet [4]. However the synthesized material is tetragonally distorted, but still a suitable material for spin torque transfer applications. The material is hard magnetic and has a saturation magnetization in average about ¼ mB / at. The Curie temperature is above the decomposition temperature of about 730 K. The electronic structure calculation indicates a ground state with ferrimagnetic order and 88% spin polarization at the Fermi Energy [5,6], however this structural instability makes Heusler compounds interesting materials for magnetic shape memory application. This instability is related to an electronic instability, which is also found in superconducting Heusler compounds [7] and magnetic Heusler compounds with a metal to semiconductor transition around the Curie temperature [8]. Semiconducting Heusler compounds will be discussed briefly in the context of diluted semiconductors [9], new magnetoresistive effects [10] and thermoelectric applications [11]. [1] C. Felser, G. H. Fecher, B. Balke, Angew. Chem. 46, 668 (2007). [2] T. Ishikawa, S. Hakamata, K.-I. Matsuda, T. Uemura, and M. Yamamoto, J. Appl. Phys. 103, 07A919 (2008). [3] S. Wurmehl, G. H. Fecher, H. C. Kandpal, V. Ksenofontov, C. Felser, H.-J. Lin, and J.Morais, Phys. Rev. B 72, 184434 (2005). [4] S. Wurmehl, G. H. Fecher, H. C. Kandpal, and C. Felser J.Phys. Cond. Matter. 18 6171 (2006). [5] B. Balke, G. H. Fecher, J. Winterlik, C. Felser, Appl. Phys. Lett. 90, 152504 (2007). [6] J. Winterlik, B. Balke, S. Wurmehl, G. H. Fecher and C. Felser, M. M. C. Alves and J. Morais, G. Azevedo and F. Furlan, Phys. Rev. B 77 054406 (2008). [7] J. Winterlik, G. H. Fecher and C. Felser, Solid State Com. 145 475 (2008). [8] J. Barth, B. Balke, G. H. Fecher, C. A. Jenskins, C. Felser, A. Shkabko, and A. Weidenkaff, submitted. [9]F. Casper and C. Felser, submitted. [10] K. Kroth, B. Balke, G. H. Fecher, V. Ksenofontov, H.-J. Lin, H.-J. Elmers, C. Felser, Appl. Phys. Lett. 89 202509 (2006). [11] B. Balke, G. H. Fecher, A. Gloskovskii, J. Barth, K. Kroth, and C. Felser, R. Robert and A. Weidenkaff, Phys. Rev. B 77 045209 (2008).


4:00 PM PP11.7
Co Doped ZnO: Magnetic and Optical Properties. Manuel Gaudon, Olivier Toulemonde and Alain Demourgues; ICMCB, Pessac, France.

ZnO doped with Co2+ has been prepared by a Pechini process and investigated in term of crystallographic structure and UV-visible properties. The Pechini route allows here obtaining an homogeneous and divided powder at 700-1200°C under air or under argon. In first, the synthesized pigments were analysed by UV-VIS-NIR spectroscopy allowing the access of the CIE -L*a*b* color parameter. Furthermore, it has been emphasized for the first time a splitting of the ZnO band-gap in two “sub band gaps” (never clearly mentioned until now) versus Co doping. The gap splitting versus cobalt substitution is fully interpreted basing on the iono-covalent nature of the O-Zn bonds. Basing on the X-Ray pattern refinements, an anticipative approach of the potential structure relaxations was discussed from exchanged effective charge per bond calculated with the ionic Brown and Altermatt model. In a last study, the magnetic behaviour for the as-prepared various Zn1-xCoxO compositions and for various temperatures (2K-300K) was recorded on SQUID apparatus and analysed. The M(H) curves show a “modified” paramagnetic behaviour with canting, weak ferromagnetic and anti-ferromagnetic contributions. The phenomenon observed and its dependence versus composition and temperature was interpreted in regard of the numerous literatures dealing with ZnO as matrix for dilute magnetic semiconductor generation.


4:15 PM PP11.8
Spintronics: Exploration for High-Temperature Dilute Magnetic Semiconductors. Glen R. Kowach, S. N Achary, Chun-Min Feng, Reem Jaafar, Daniel Margul, Bas van Eck and Anielisa Jones; Chemistry, The City College of New York, New York, New York.

Recent theoretical and empirical interest in dilute magnetic semiconductors for spintronics applications has been generated due to the potential technological impact in the electronics industry. Initial theoretical reports published after the discovery of carrier-mediated ferromagnetism in manganese-substituted GaAs suggested high Curie temperatures for manganese-substituted ZnO and GaN. Several research groups proceeded to prepare these compounds; however, further analysis suggests that the ferromagnetism is due to impurities, such as phase separation leading to clustering of ferromagnetic inclusions. We will present our results on the synthesis and substitution of binary and ternary phosphides, specifically tin phosphides, zinc phosphides, and phosphides with the chalcopyrite structure. Further, we will present magnetic properties indicating phase separation as the most significant synthetic challenge for future spintronics materials.


4:30 PM PP11.9
On the Absence of Ferromagnetism in Cr and Fe Doped In2O3. Amy Goodwin, Nick Arnott, David Payne and Russell Egdell; Inorganic Chemistry Laboratory, University of Oxford, Oxford, United Kingdom.

In recent years there has been much interest in the field of dilute ferromagnetic oxides (DFMOs) where it is claimed that non magnetic oxides doped with a few percent of a transition metal cation can show ferromagnetism at room temperature and above. This phenomenon was first seen in Co-doped TiO2 by Matsumoto et al. in 2001 [1] and at a similar time theoretical predictions by Dietl et al. [2] suggested that room temperature ferromagnetism could be achieved in Mn-doped ZnO and GaN provided that the magnetic centres were coupled by itinerant charge carriers. To date the majority of studies of ferromagnetic oxide semiconductors have been on thin films, usually (but not always) prepared by pulsed laser deposition. However to gain a full understanding of these materials it is vital to investigate the magnetic and electronic properties of well characterised bulk material. The suspicion remains that in many cases ferromagnetism in oxide thin films arises from magnetic clusters or inclusions or the effects of surface and inerfaces. In the present study we investigate the magentism of Cr and Fe doped In2O3. These two materials had previously been investigated by Phillip et al. (Cr doped samples) and Jayakumur et al. (Fe doped samples) and room tempearture ferromagentism was observed for both [3,4]. Phase pure ceramic pellets of MxIn2-xO3 (M=Cr, Fe) were prepared using standard bulk synthesis methods. Substitutional incorporation of Fe and Cr at 2% and 4% doping level was confirmed by small decreases in bulk lattice parameters. Charge carriers were introduced either by co-doping with Sn or by annealing the pellets under an argon-hydrogen atmosphere in order to introduce O-vacancy donor states. The bulk samples were analysed using powder X-ray diffraction, SQUID magnetometry between 5K and 300K and Al Kα X-ray photoelectron spectroscopy (XPS). There was no indication of ferromagnetism in Cr- and Fe-doped material even after co-doping with Sn or in Cr-doped material subject to reduction. However magnetic anomalies were observed in reduced Fe-doped material. However this appeared to be associated with formation of a secondary Fe3O4 phase. We are forced to conclude that ferromagnetism is not an intrinsic property of bulk Cr or Fe-doped In2O3, even after co-doping with electron donors. [1] Y. Matsumoto et al. Science 291 , 854 (2001). [2] T. Dietl et al. Science 287 , 1019 (2000). [3] J. Phillip et al. Nat. Mater.5 , 298 (2006). [4] O.D. Jayakumar et al. Appl. Phys. Lett.91 , 3 (2007).


4:45 PM PP11.10
Spectroscopic and Magnetic Studies of Free-Standing Magnetic Transparent Conducting Oxide Nanocrystals. Shokouh S Farvid, Neeshma Dave, Ling Ju and Pavle V. Radovanovic; Chemistry, University of Waterloo, Waterloo, Ontario, Canada.

Multifunctional materials of reduced dimensionality have become an increasingly active area of research in nanoscale solid-state chemistry and physics. Spin-electronics (spintronics), for example, relies on the mutual interactions of electron spins and charges. Nanostructured diluted magnetic semiconductors (DMSs) having high ferromagnetic phase transition temperatures (TC¬) have been identified as promising materials for this emerging technology. Specifically, free-standing DMS nanocrystals (DMS-NCs) can be used as building blocks for a bottom-up assembly of functional devices, and may enable microscopic understanding of transition-metal dopant spin ordering in semiconductors. Transparent conducting oxides (TCOs), such as TiO2, SnO2, and In2O3 are particularly interesting as host lattices for potential high-TC ferromagnetic wide band-gap semiconductors, due to their stability, high electrical conductivity, and transparency to visible light. These characteristics make it promising for the preparation of DMSs in which long-range magnetic ordering is charge carrier mediated, and for the fabrication of integrated opto-spintronic devices. Here we report the synthesis and characterization of free-standing colloidal Cr3+-doped TCO NCs. Cr3+ is chosen as a dopant ion due to its kinetic inertness, relatively large magnetic moment and high affinity for six-coordinate substitutional sites in studied TCO lattices. Nanocrystalline films fabricated from these nanocrystals exhibit a robust intrinsic ferromagnetism in with a Curie temperature (TC) above 300 K. Combined site-specific ligand-field spectroscopy and a single nanocrystal characterization provide an important insight into the origin of the macroscopically observed magnetic properties in these materials.


 

SESSION PP12: Poster Session: Non-Oxides
Chair: Richard Dronskowski
Thursday Evening, December 4, 2008
8:00 PM
Exhibition Hall D (Hynes)


PP12.1
Plasma Synthesized Boron Nano-sized Powder: The Effect of Processing Conditions on the Crystallographic and Microstructural Properties. James V. Marzik1, Richard C Lewis1, Matthew J Kramer2, Ya-qiao Wu2, Douglas K Finnemore2 and William J Croft3; 1Specialty Materials, Inc., Lowell, Massachusetts; 2Ames Laboratory and Iowa State University, Ames, Iowa; 3Harvard University, Cambridge, Massachusetts.

Boron nano-sized powders were synthesized by the reaction of boron trichloride and hydrogen in a radio-frequency plasma. These powders have been used as precursors for the formation of magnesium diboride superconducting wires. Plasma synthesized boron particles typically had the shape of low aspect ratio spheroids that tended to agglomerate. The majority of particle sizes ranged between 20 and 100 nm. A typical batch of boron powder contained a mixture of amorphous and crystalline material. In this study, the effects of process conditions such as plasma power, reactant gas flows, and pressure, on the crystallinity, particle size, and microstructure of boron nanopowder was investigated using powder x-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and selected area electron diffraction (SAD). Particle size distribution was measured using SEM, TEM, and laser light scattering methods. Both undoped and carbon-doped boron powders were characterized.


PP12.2
Fabrication and Characterization of Electrically Functional Boride System Thin Films on the Ultra-smooth Sapphire Substrate. Yushi Kato1, Yasuyuki Akita1, Yusaburou Ono1, Makoto Hosaka1, Naoki Shiraishi1, Nobuo Tsuchimine2 and Mamoru Yoshimoto1; 1Department of Innovative and Engineered Materials, Tokyo Institute of Technology, Yokohama, Japan; 2TOSHIMA Manufacturing Company Limited, Saitama, Japan.

The cubic hexaborides have attractive wide variety of physical properties in spite of their simple crystallographic structures. Especially, LaB6 has already been put to practical use in high intensity electron source because of extremely small work function (2.6eV). Recently, the concern with the application of thermoelectric conversion materials using hexaborides has been growing for solving the energy problems. In particular, SrB6 whose thermoelectric property was greater than currently used boron carbide was reported n-type thermoelectric materials in boron-rich solids [1]. Hexaborides have a wide variation in an electrical property by doping divalent or trivalent metallic ion into the crystal structure which is a simple cubic CsCl-type arrangement of B6-octahedra and metal ions. In addition, ferromagnetism at high temperature was reported for the doped hexaborides in recent years [2]. Before, several studies have been reported on bulk states or poly-crystalline thin films of boride materials, but the property of the single-crystalline or epitaxial films has not been clarified well. There are reported few attempts to prepare hexaboride epitaxial thin films, which might be desired for electronic device applications. Before we have investigated about epitaxial growth of functional ceramic thin films by Laser MBE at low temperature on the ultra-smooth sapphire (0001) substrates which have atomic steps of 0.2 nm in height and atomically flat terraces of 50-100 nm in width [3]. In this work, we focused our attention on fabrication and characterization of LaB6, SrB6 and (La,Sr)B6 thin films. Fabrication of hexaboride thin films was carried out on the ultra-smooth sapphire (0001) substrates with atomic steps and atomically flat terraces using Laser MBE. Characterizations were made with X-ray diffraction (XRD), reflection high-energy electron diffraction (RHEED), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) in order to examine the epitaxy, surface composition and surface morphologies of the prepared thin films. The electrical resistivity was measured by the conventional 4-probe method. As a result, the C-axis oriented LaB6 thin films could be grown along the atomic steps of the sapphire substrate. The electrical property of the prepared specimens indicated very low resistivity comparing with the thin films on the commercial substrates. This specimen shows a metallic behavior and the resistivity was almost constant at low temperatures. On the other hand, the resistivity-temperature curve of B-deficient LaB6-x thin films was semiconductive at low temperatures. RHEED pattern of the prepared SrB6 thin films was streaky. Thus, it is noted that SrB6 thin film could be grown epitaxially. The electrical property of the SrB6 epitaxial film was characterized. [1] M. Takeda et al., J. Solid State Chem., 177(2004)471-475 [2] D. P. Young et al., Nature, 397(1999)412-414 [3] M. Yoshimoto et al., Nature, 399(1999)340-342


PP12.3
Abstract Withdrawn


PP12.4
Structural Study of Hydrogenated Amorphous Silicon Carbide Multilayer Films. Mitsuya Motohashi, Tatsuya Wagai and Kazuaki Homma; Engineering, Tokyo Denki University, Tokyo, Japan.

Currently, hydrogenated amorphous silicon carbide (a-SiC:H) multilayer films are being actively researched as materials for use in solar cells and photosensors because they have excellent photoconductive characteristics. There is a social demand for efficient and multifunctional devices, and the number of layers in devices is generally increased in order to satisfy these requirements. However, the effect of the lower layer on the upper layer in an a-SiC:H multilayer has not yet been discussed in sufficient detail. Therefore, it is necessary to examine the process of deposition of a layer on the surface of film growth. We aimed to clarify the growth process of the a-SiC:H multilayer and the structural effect of the lower layer on upper layer. Source-gases separated plasma chemical vapor deposition (SSP-CVD) was used to deposit the a-SiC:H multilayer. SiH4 and CH4 were used as source gases. The flow rate ratio γ=[CH4]/{[SiH4]+[CH4]} was changed for the deposition of each layer within a single deposition. The substrate temperature was 250C. The number of layers was 2 or 6. The thickness of the lowest layer was 200nm, and the thickness of each upper layer was 50nm. We have been investigating the atomic bonding configuration of the a-SiC:H multilayer by using real-time in-situ infrared-reflection-absorption spectroscopy (IR-RAS). We have also studied the changes in the thermal structure of the a-SiC:H multilayer by X-ray photoelectron spectroscopy. The sample was heated from the room temperature to 1200C by using an infrared lamp furnace (MILA3000; ALVAC, Inc.) in the presence of nitrogen gas. The IR-RAS spectrum of the a-SiC:H multilayer was measured, and the result has been described below. When the γ of the lower layer was small, the amount of hydrogen was increased greatly and the number of the Si-H2, C-Si-H, and bond such as C-Si-H2 increasesed compared with the Si-H bond. On the basis of these results, we discuss the growth process of the a-SiC:H film as follows. The Si atom sticks easily to the surface of film growth regardless of the type of the atoms of which the surface is composed. Further, it was assumed that C and H atoms were incorporated easily in the film when the number of Si atoms was more than that of the C atoms on the surface of film growth. In short, it was expected that the sticking probability of the radical in the plasma differed according to the atomic composition of the lower layer. This composition has been understood to greatly change the atomic bonding configuration of the upper layer between 800 and 1200C. However, we could not study in detail the effects of the difference in the composition of the lower layer on the upper layer. It is necessary to discuss this aspect in detail in the future. This work was supported in part by the Research Institute for Science and Technology of Tokyo Denki University under Grant Q02M-01 and Q06M-01.


PP12.5
Synthesis of GaN-based Photocatalysts from Metallic Ga. Takeshi Hirai1,2, Daiki Kato2, Shigeru Ikeda2, Kazuhiko Maeda3, Kazunari Domen3 and Michio Matsumura2; 1Department of Physical Sciences, Ritsumeikan University, Kusatsu, Shiga, Japan; 2Research Center for Solar Energy Chemistry, Osaka University, Toyonaka, Osaka, Japan; 3Department of Chemical System Engineering, The University of Tokyo, Bunkyo-ku, Tokyo, Japan.

Production of hydrogen from water using the sunlight has been a dream of scientists. Water-splitting using photocatalysts is an approach to the goal, and gallium nitride (GaN) has attracted much attention as a host material of the photocatalysts. Although undoped GaN does not show photocatalytic activity for overall water-splitting, GaN doped with divalent metal ions (Mg, Zn or Be) shows the activity under the irradiation of ultraviolet (UV) light at wavelengths shorter than 400 nm. In addition, GaN-rich (Ga1-xZnx)(N1-xOx), which is a solid solution of GaN formed by partially substituting Ga with Zn and N with O, is capable of splitting water under irradiation of visible light at wavelengths shorter than 500 nm. These previous reports suggest that doping GaN with impurities, particularly divalent metal ions such as Zn, is crucial to create the activity for photosplitting water in GaN. In the previous studies, gallium sulfide (Ga2S3) and gallium oxide (Ga2O3) have been used as starting materials for the synthesis of the GaN-based photocatalysts. However, the GaN-based photocatalysts synthesized by nitriding the starting materials should include unintentionally incorporated O or S impurities. To clarify the roles of the impurities in GaN-based photocatalysts and also to increase the photocatalytic activity, it is necessary to develop a new synthesis method that does not allow the incorporation of the unintentional impurities into the GaN-based photocatalysts. Hence, we have carried out the synthesis of the GaN-based photocatalysts, which contains Zn impurities, using metallic Ga as the starting material. The photocatalytic performance of the synthesized photocatalysts for splitting water will be discussed together with their physical properties, which are characterized by x-ray diffraction, scanning electron microscopy, diffuse reflection spectroscopy, and photoluminescence spectroscopy.


PP12.6
Chemical Vapour Deposition of Oxygen Doped Copper (I) Nitride. Anna Fallberg, Mikael Ottosson and Jan-Otto Carlsson; Materials Chemistry, Uppsala, Sweden.

Copper nitride (Cu3N) has been in focus as a fascinating material over decades, especially in the field of thin films and has been fabricated with different techniques and with various reaction schemes. Its intrinsic properties as a metastable semiconductor have been well characterized and potential applications have been developed, but still there are more things to be discovered about copper nitride. The metastability and the possibility of varying the band gap of Cu3N may offer a unique set of applications to be exploited in areas like microelectronics, optical data storage, and solar energy technology. In this study, the chemical vapour deposition (CVD) method has been used to deposit oxygen doped Cu3N, where we exploit the advantage of high deposition rate and good control of gas-phase composition that this technique offers. The films were grown in a low-pressure, hot-wall, two-zone tubular quartz reactor with Cu(hfac)2, H2O and NH3 used as precursors. The aim of the study was to investigate the phase stability between Cu2O and Cu3N and most importantly, to see how much oxygen that could be incorporated within the Cu3N structure. The focus has been on how addition of oxygen in the Cu3N films influences the morphology, resistivity and the optical band gap of the deposit. The deposited films have been characterized with respect to phase content, stoichiometry, surface morphology, resistivity and optical band gap by analysis techniques as; XRD, XPS, ERDA, SEM, four point probe and optical spectroscopy.


PP12.7
Mn-Substitution of Ternary Phosphides Having the Chalcopyrite Structure. S. N Achary, Anielisa Jones, Chun-Min Feng, Daniel Margul, Bas van Eck and Glen R. Kowach; Chemistry, The City College of New York, New York, New York.

The synthesis of single crystal and polycrystalline zinc silicon phosphide (ZnSiP2) and cadmium silicon phosphide (CdSiP2) from the constituent elements was pursued. To increase the portion of the desired phase, two different heat treatments were exploited in this solid state reaction. Crystal growth of ZnSiP2 and CdSiP2 from sodium and tin fluxes was also studied. CdSiP2 or ZnSiP2 crystals were obtained from Sn flux synthesis but Na flux growth lead to decomposition. Various nominal Mn concentrations, from 2 at.%, to 30 at.%, were introduced into ZnSiP2 and CdSiP2 lattices. Fullprof-2000 software package is utilized for Rietveld refinement and Lebail refinements of the x-ray diffraction data. The unit cell volume of ZnSiP2 increases with increasing Mn concentration from 304.2 Å3 (ZnSiP2) to 305.35 Å3 (Zn0.95Mn0.05SiP2) after which it does not show any significant variation. On substitution Mn in CdSiP2, the unit cell volume decreases from 337.6 Å3 (CdSiP2) to 335.01 Å3 (Cd0.70Mn0.30SiP2). Instead of substitution on group IV site, Mn substitution on group II site has been demonstrated. Temperature dependent susceptibility data revealed a ferromagnetic transition near 300 K followed by an antiferromagnetic transition near 50 K. Hysteresis loops at room temperature are observed in all Mn substituted samples. The magnetic behavior of the Mn substituted samples is comparable with the crystalline MnP sample, even though MnP remains unidentified in X-ray diffraction data.


PP12.8
Deposition of Phosphorous Free PbSe Thin film by Aerosol Assisted Chemical Vapour Deposition. Javeed Akhter, Mohammad Azad Malik and Paul O'Brien; Chemistry, The University of Manchester, Manchester, United Kingdom.

PbSe is an important semiconductor and finds applications such as in: IR radiation and photoconductor detectors as well as photovolatiac materials. The deposition of PbSe thin films from diselenophosphinato- and imidodiselenodiphosphinatolead(II) complexes1 always results with significant contamination with phosphorous. In order to overcome this problem we have synthesized 4-nitro N, N diisobutyl-N-benzoylselenoureato)Pb(II) and N,N diethyl-N-benzoylselenoureato) Pb(II) complexes to be used as single source precursors for the deposition of PbSe thin films. Thermo gravimetric analysis of these complexes showed single step decomposition into PbSe in the temperature range between 240-310 oC. Thin films were deposited onto glass substrates between the temperature range 300-500 oC. XRD pattern of the as deposited films showed cubic phase of PbSe. SEM revealed that the shape and size of crystallites changed from cubes to rods depending on the deposition temperature and energy dispersive X-ray analysis (EDX) confirmed the composition of PbSe in the films as 1:1. References: 1..Afzaal, M.; Ellwood, K.; Pickett, N. L.; O'Brien, P.; Raftery, J.; Waters, J. 2004, 14, 1310-1315


PP12.9
Ultra-high pressure MOCVD - A Supercritical Route to Compound Semiconductor Materials. James William Wilson1, Jixin Yang2, Jason R Hyde1, David C Smith1, Steven M Howdle2, Kanad Mallik4, Pier A Sazio4, Paul O'Brien3, Mohammed Malik3, Mohammed Afzaad3 and Chinh Q Nguyen3; 1School of Physics and Astronomy, University of Southampton, Southampton, Hampshire, United Kingdom; 2School of Chemistry, University of Nottingham, Nottingham, Nottinghamshire, United Kingdom; 3Department of Chemistry and the Manchester Materials Science Centre, University of Manchester, Manchester, Greater Manchester, United Kingdom; 4Optoelectronics Research Center, University of Southampton, Southampton, Hampshire, United Kingdom.

The deposition of thin films of materials on to and in to preformed, high-aspect ratio, template materials, is of significant interest to the semiconductor community. Damascene processes are vital to the electronic industries, and new synthetic methods are being developed in order to achieve modification of rationally designed templates; modifications that are limited by current MOCVD or CBD deposition technologies. Supercritical chemical fluid deposition, SCFD, offers a route to these devices by exploitation of their zero surface tension, tuneable physical properties, and ability to dissolve relatively high concentrations of reagents. In addition to Cu metalisations[1], Si-Ge core-shell wires and nanotubes[2] 3nm in diameter, can be produced by batch SCFD. However, this approach has yet to be extended to include compound-semiconductor deposition, i.e. II-VI materials. <p> We report the design, deposition and characterisation of high quality CdS thin-films from a SCF in a continuous flow reactor as the first synthetic stage towards deposition in complex topologies. Our approach employs a tailored single source precursor with an enhanced solubility in SCFs, eliminating the need to control individual reagent concentrations in the kinetically limited regime within the flow reactor. <p> Chemical composition of thin films deposited on SiO2/Si substrates have been examined by AES, and show that films deposited by this technique are close to stoichiometric. Furthermore, SEM demonstrates that these films are formed from highly compacted hexagonal pyramidal crystals, which are in the order of 200 nm. XRD confirms pure α-CdS. Judicial engineering and design has eliminated extrinsic dopants and other contamination leached from the stainless steel pressure vessels; this has been confirmed by SIMS measurements. CdS films are highly reflective and exhibit interference fringes due to small thickness variations. Photoelectrochemical spectroscopy were performed and the band-edge absorption was found to be 504 nm, in agreement with published values for CdS. Moreover, unlike most CBD deposited material, films deposited from our SCF reactors exhibit room temperature band-edge luminescence with a FWHM of 15.8 nm decreasing to 5.5 nm at 2.9 K, smaller than that of PLD material which exhibits lasing.[3] <p> This presentation demonstrates a general approach to deposition from SCFs, by the development and design of both reagent chemistry and reactor engineering, opening the way for a wider class of semiconductors to be deposited into complex 3D-topologies conforming to a rational design. <p> [1] Cabanas et al., Chem. Mater., 16, 2028 (2004)<p> [2] Audoit et al., J. Mater. Chem., 15, 4809 (2005)<p> [3] Ullrich et al., J. Lumin., 87-89, 1162 (2000)<p>


PP12.10
Room-Temperature Synthesis and Thermoelectric Properties of Microspheres of Biphasic Bi2Te3-Sb2Te3 Nanostructures. T. Wang1, R. Mehta1, C. Karthik1, B. Singh1, W. Jiang1, T. Borca-Tasciuc2 and G. Ramanath1; 1Department of Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, New York; 2Department of Mechanical Aerospace and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, New York.

Bismuth/antimony telluride-based compounds are promising for applications in solid-state cooling and power generation due to their high thermoelectric figure of merit ZT, given by α2σ/κ, where α is the Seebeck coefficient, σ the electrical conductivity, and κ the thermal conductivity. However, solid-state cooling technologies require materials with two- to four-fold higher ZT than that of bulk bismuth telluride (ZT~1) to compete with conventional compressor-based refrigerators and power sources. Nanostructuring high ZT materials along one dimension (e.g., <20-nm-thick nanolayers of two high ZT materials Bi2Te3 and Sb2Te3) has been shown to increase ZT due to boundary scattering-induced κ decrease. Here, we describe the room-temperature synthesis of microspheres comprised of biphasic nanostructures with multidimensional confinement (1-D to 3-D). Such architectures are conducive for decreasing κ by providing phonon scattering sites over multiple length scales, and the possibility of creating macroscopic samples while reaping the benefits of nanostructuring. In particular, we will describe the synthesis of 0.5-3 μm porous microparticles comprised of interconnected sub-10-nm nanoplates in a flowery morphology, and subsequently filling of the pores with nanostructured Sb2Te3. In the first step, the microparticles were synthesized by reducing BiCl3 and orthotelluric acid with hydrazine followed by aging. In the second step, hydrazine reduction of SbCl3 and telluric acid in the presence of flower-like Bi2Te3 nanostructures results in Sb2Te3 filling the pores, forming Bi2Te3/Sb2Te3 biphasic nanocomposites. The size of the nanoplatelets and the microspheres is controllable by adjusting the precursor ratios and reaction parameters. In addition to electron microscopy investigations capturing the above morphological and crystallographic features, we will discuss the results of X-ray photoelectron and infrared spectroscopy measurements carried out to characterize the bulk and surface chemistry of the nanocomposites. Finally, we will report on the electrical conductivity and Seebeck coefficient of individual microspheres as well as their thin film assemblies contacted with nanofabricated electrodes. The observed electrical and thermoelectric behavior are modeled in terms of the morphology of the biphasic nanostructures.


PP12.11
Ultrafast Microwave-Stimulated Sculpting and Thermoelectric Properties of Bismuth and Antimony Chalcogenide Nanoplatelets. R. J Mehta1, C. Karthik1, B. Singh1, E. Castillo2, W. Jiang1, T. Borca-Tasciuc2 and G. Ramanath1; 1Department of Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, New York; 2Department of Mechanical Aerospace and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, New York.

Nanostructured forms of V-VI semiconductors are attractive for realizing high figure of merit thermoelectrics for novel applications such as harvesting electrical power from heat, and solid state refrigeration of hot-spots in nanodevices. Although many wet-chemical and templating techniques have been devised over the last several years to synthesize chalcogenide nanostructures with shape and/or size control, these approaches are limited by lack of scalability, poor crystal quality and template removal issues. Here, we report the rapid (< ~ 2 minutes) scalable solvothermal synthesis of 5-20-nm-thick hexagonal shaped nanoplatelets of Bi2Te3, Bi2Se3, and Sb2Te3 by microwave-stimulation. We further demonstrate the induction or suppression of branching by manipulating the surfactant concentration. Such nanostructures pave the way for combining thermoelectric cooling with high-surface area heat spreading for solid-state refrigeration and power generation applications. We synthesized the nanoplatelets by exposing a mixture of trioctylphosphine, pentanediol with the bismuth and tellurium precursors and thioglycolic acid to 2.4 GHz microwave radiation. The nanoplatelet edge lengths are tunable between 100 nm to 1 μm by adjusting the microwave dose, which, however, has negligible effect on the nanoplatelet thickness. Electron microscopy and diffraction analyses reveal that each nanoplatelet is a rhombohedral single crystal with a R-3m structure that grows in a layer-by-layer fashion. The smallest layer step within each nanoplatelet is ~1 nm, reminiscent of the basic building block with the atomic layers within a unit cell. Electron diffraction patterns show forbidden reflections attributed to the presence of anti-site defects. X-ray photoelectron spectroscopy and infrared spectroscopy reveal the lack of an oxide layer due to surface passivation by molecular capping agents. We were able to controllably induce platelet branching by adjusting the thioglycolic acid concentration, underscoring the importance of the capping agent in nanostructure shape selection. Finally, we will present the electrical and thermoelectric responses measured from test structures with electrically contacted individual nanoplatelets, and discuss the effects of thickness, edge length and branching in the context of theoretically predicted figures of merit for these structures.


PP12.12
Microstructure and Thermoelectric Properties of Nanocarbon Ensembles. Paola Bruno1, Raul Arenal1,2,3, Victor A Maroni4, Dean J Miller3, Jules L Routbort5, Dileep Singh6, Ming Xie1,7 and Dieter M Gruen1; 1Materials Science Division, Argonne National Laboratory, Argonne, Illinois; 2Laboratoire d' Etude des Microstructures, ONERA-CNRS, Chatillon, France; 3Electron Microscopy Center, Argonne National Laboratory, Argonne, Illinois; 4Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, Illinois; 5Energy System Division, Argonne National Laboratory, Argonne, Illinois; 6Nuclear Engineering Division, Argonne National Laboratory, Argonne, Illinois; 7Department of Physics, Michigan Technological University, Houghton, Michigan.

Nanocarbon ensembles (NCE’s) have been shown to display unusual thermoelectric properties. The thermopower factor in boron doped materials is strongly temperature dependent and increases by more than an order of magnitude over undoped ensembles. Preliminary structural data were interpreted in terms of boron doping of a nanographite constituent (1). The present work reports detailed HRTEM, Raman and XRD measurements on a series of NCE’s synthesized at temperatures up to 1700 K. HRTEM micrographs show a complex microstructure for the NCE’s made up of the originally present UNCD particles and a mixture of nanographite and amorphous carbon produced by heating compacted UNCD in a stream of methane up to 1200K. The structure of the 5 nm nanographite particles formed under these conditions is best described as resembling stacked sheets of graphene. Heating the NCE’s to temperatures of 1700 K progressively converts the UNCD particles to nanographite. A different, “onion-like” nanographite structure emerges as a result of UNCD graphitization as shown in earlier work (2). The evolution of the NCE microstucture as a result of the higher temperature treatment is followed by all three characterization techniques and in particular by XRD measurements. The effect of the NCE microstructure and the boron doping level on the thermoelectric properties of NCE’s will be discussed in terms of recently obtained Seebeck coefficient and electrical conductivity data. References (1) D.M. Gruen, P. Bruno, M. Xie, APL 2008, 92 (143118). (2) Kuznetsov et al, chap. 13, pg. 438, Ultrananocrystalline Diamond, Synthesis, Properties and Applications, Edited by O. Shenderova, D.M. Gruen, 2006 Acknowledgements Work performed under the auspices of the U.S. Department of Energy, Office of Science and Energy Efficiency Renewable Energy, Office of Vehicle Technologies under Contract No. DE-AC02-06CH11357.


PP12.13
Abstract Withdrawn

PP12.14
Experimental and Theoretical Studies of the Itinerant-Localized Duality of 4f-electron in CeIn3. Delphine Gout1,2, Thomas Proffen3, Joe Thompson3, Eric Bauer3 and Olivier Gourdon1; 1ORNL, Oak Ridge, Tennessee; 2Juelich Inst., Juelich, Germany; 3Los Alamos National Laboratory, Los Alamos, New Mexico.

Recently, we have investigated by both neutron and X-ray diffraction the crystal structures of a series of La1-xCexIn3 (x=0.02, 0.2, 0.5, 0.8) intermetallic compounds. Our results emphasize atypical atomic displacement parameters (ADP) for the In and the rare-earth (R.E.) sites. Depending of the x value, the In ADP presents either “an ellipsoidal” elongation (La rich compounds) or a “butterfly-like” distortion (Ce rich compounds). These deformations have been understood by theoretical techniques based on the band theory and are the result of hybridization between conduction electrons and 4f-electrons.


PP12.15
A New Stable Decagonal Quasicrystal in Pd-Al-Zn System. Srinivasa Thimmaiah and Gordon J Miller; Chemistry, Ames Laboratory/Iowa State University, Ames, Iowa.

The discovery of the first quasicrystal, i-AlMn, by Schechtman et al. in 1984[1] has energized research in the field of complex intermetallics toward uncovering other systems with structures and compositions that exhibit quasiperiodicity. Numerous quasicrystalline phases have been discovered and characterized that show icosahedral, dodecagonal, and octagonal symmetry in their diffraction patterns[2]. Here, we report preliminary result on a decagonal quasicrystal/approximant in Pd-Zn-Al ternary system. Crystals with nominal composition Pd20Zn25Al55 revealed the forbidden decagonal symmetry. Our preliminary results show that the reflections can be indexed in a C-centered orthorhombic cell, space group C222_1, with lattice parameter a = 23.582(5) Å, b = 32.416(7) Å, and c = 16.647(3) Å. The structural refinement converges to residual R1 = 22 % with more that 600 atoms in the unit cell. References: [1] Shechtman, D.; Blech, I.; Gratias, D.; Cahn, J. W. Phys. Rev. Lett. 1984, 53, 1951. [2] Steurer, W. Z. kristallogr. 2004, 219, 391


 

SESSION PP13: Poster Session: Ionic Conductors
Chair: Richard Dronskowski
Thursday Evening, December 4, 2008
8:00 PM
Exhibition Hall D (Hynes)


PP13.1
Abstract Withdrawn


PP13.2
Abstract Withdrawn


PP13.3
Electrochemical Performance of Co3O4 Thin Film Electrode Prepared by Radio Frequency Magnetron Sputtering Method for Lithium Ion Batteries. Dong-Qiang Liu, Sung-Hun Yu, Se-Wan Son and Seung-Ki Joo; School of Materials Science and Engineering, Seoul National University, Seoul, South Korea.

Nano-sized transition metal oxides, such as FeO, NiO, Co3O4, SnO2, CuO and Cu2O et al, have been reported as new anode materials for lithium ion batteries (LIB) because of their higher capacity compared to carbon anode. Among these metal oxide materials, Co3O4 shows the highest specific capacity about 1100 mAh g-1 when discharging to 0 V versus Li metal. Co3O4 can be prepared by pulse laser deposition, electrochemical deposition, sol-gel, and electron beam evaporation for application in LIB. Radio frequency (rf) magnetron sputtering technique is a simple, one-step and cost-effective method for thin film electrode preparation. However, there are few reports about the rf-sputtered Co3O4 thin film electrodes for LIB. In this study, Co3O4 thin film electrodes were deposited by rf-sputtering method at room temperature (Sample A), 100oC (Sample B), 200oC (Sample C), and 300oC (Sample D), respectively. X-ray diffraction results indicate that the structure of Co3O4 electrodes change from amorphous to crystalline for sample A and sample D. Field emission scanning electron microscope suggests the nano-scale Co3O4 thin film were successfully prepared at 300oC (Sample D). In order to investigate the electrochemical properties of Co3O4 thin film electrodes, each ample was assembled as a half-cell with lithium metal in argon-filled glove box. Cyclic voltammetry results showed the typical curves of Li/Co3O4 battery. Galvanostatic cycling experiments of the as prepared thin film electrodes were carried out in glove box at the current density of 200 μA cm-2 using a WBCS 3000 instrument. A distinct capacity loss was observed for each half-cell during the first cycle because of the irreversible reaction between electrolyte and electrode surface. In the subsequent 50 cycles, sample A, B and C still showed drastic capacity decline. However, sample D possessed excellent capacity retention, compared with sample A, B, and C, due to the crystalline structure of Co3O4. After 50 cycles, only 5.6% capacity loss was found for sample A. Electrochemical impedance spectroscopy measurements were also conducted using a Zahner IM5d (Zahner Elektrik) electrochemical workstation to understand more about the electrochemical behavior of the Co3O4 thin film electrodes. Impedance spectra were recorded in the frequency range of 2 MHz to 100 mHz with an ac amplitude of 10mV. After 50 cycles, the impedance increased slowly for sample D, compared with sample A, B and C, which is in good agreement with the galvanostatic cycling results. The electrochemical experiments indicate that the rf-sputtering method is a promising way to prepare Co3O4 thin film electrodes for lithium ion batteries.


PP13.4
Direct TEM Observation of SEI Films on Carbon Nanoparticles in Negative Electrodes of Li-ion Batteries. Noriko Yoshizawa1, Yasushi Soneda1, Hiroaki Hatori1, Koji Miura2 and Takeshi Abe3; 1AIST, Tsukuba, Japan; 2Tokai Carbon Co.Ltd., Sunto, Japan; 3Kyoto University, Kyoto, Japan.

Carbon nanoparticles with concentric orientation of aromatic layers are known as the promising materials to achieve the superior high-rate charge-discharge performance in Li ion batteries, as well as their possibility to be used in a wide range of electrolyte including PC-based ones. These advantages in carbon nanoparticles are partly attributed to a formation of solid electrolyte interphase (SEI) due to decomposition of solvents during the first charging process in Li ion batteries. We have successfully observed a series of SEI with TEM, and demonstrated the dependence of their morphology upon the distribution of surface structural defects of carbon particles with 200 nm diameter. However, influences of a size of carbon nanoparticles, a type of electrolyte, and the number of cycles was not been enough clarified. In this study, we investigated the SEI structure formed on the carbon nanoparticles mainly by TEM observation. Pristine carbon nanospheres (CNSs; Tokai Carbon Co. Ltd., 200 and 500 nm in diameter) and their heat-treated samples between 1373 and 3073 K were used for negative electrodes. Negative electrodes were composed of CNS samples (80% w/w), PVDF (10% w/w) and carbon black (10% w/w). They were mixed to make slurry, and then spread onto Ni mesh. The charge-discharge process was done in the three-electrode cell with CNS as working electrode, Li metal as counter and reference electrodes. As electrolyte, 1M-LiX-/EC+DEC (1:1) (X- = BF4-, PF6-) or 1M-LiBF4/PC was used. TEM observation of CNS in 500 nm diameter after the first charge-discharge cycle in LiX-/EC+DEC did not show any changes in the morphology of carbon particles. Concerning SEI structure, on the other hand, its morphology and thickness are sensitively influenced by the density of carbon layer edges exposed on the surface of graphitized CNS particles. CNS particles heat-treated at 3073 K were totally covered with amorphous or less-crystalline film with uniform thickness (2-3 nm), while the ones at 1373 K were coated with SEI with irregular surface. Our previous studies showed that these features in SEI morphology and thickness were also seen on CNS in 200 nm diameter. It is also noted that SEI features as mentioned above were maintained even after 100 cycles for CNSs heat-treated at 3073 K. By using LiBF4/PC as electrolyte, it seems that carbon structure sometimes suffers damage even at the first charge-discharge cycle: TEM observation showed an exfoliation of a stack of carbon layers on the surface of graphitized CNS particles. Microanalysis of SEI films in these samples was additionally carried out by EDS and EELS. Presence of lithium, carbon and oxygen was confirmed, while there was little fluorine in the SEI formed in LiBF4/EC+DEC. It was also found that SEI films formed in LiPF6/EC+DEC (1:1) were composed of lithium, carbon, oxygen and phosphorus.


PP13.5
Magnetic Clustering in Layered Cathode Materials for Lithium-Ion Batteries as a Probe of Local Structural Ordering. Natalya A. Chernova and M. Stanley Whittingham; Chemistry and Materials, SUNY Binghamton, Binghamton, New York.

Transition metal ordering has a significant effect on the electrochemical properties of layered oxide cathode materials. Different superstructure models, for example, flower and zigzag, proposed for LiNi0.5Mn0.5O2 and NaNi0.5Mn0.5O2, respectively, and honeycomb found in Li2MnO3 reveal distinctively different magnetic order at low temperatures, which allows using magnetic properties as an indicator of structural ordering. However, a long-range transition metal order has not been observed in Li1+x(Ni, Mn, Co)1-xO2 cathode materials, although ordering tendencies have been found by Li NMR and local ordered domains were observed in electron diffraction. In this case long-range magnetic order is not possible either. The spins order within finite-size clusters or domains in magnetically concentrated systems or undergo spin-glass transition when the layers are well diluted with non-magnetic Li+ and Co3+. In this work we show that two main kinds of ferrimagnetic clusters, i.e. interlayer, coupled by 180° magnetic exchange through Ni ions in the lithium layer, and intralayer, coupled by 90° exchange, undergo magnetic ordering at different temperatures. This is reflected by two well-resolved maxima in the temperature dependences of the magnetic susceptibility (ac or dc) measured in a small field after zero-field cooling. The amplitude and temperature of these maxima increase with the size of magnetic clusters, which depends upon the amount Ni in the Li layer and the amount of non-magnetic ions in the transition metal layer. In the frames of this model we rationalize magnetic properties of Li1+x(Ni, Mn, Co)1-xO2 compounds as a function of composition and suggest the distributions of transition metal and Li ions in the layers. These results are used to corroborate and enhance the data obtained by the x-ray diffraction and NMR. Several examples, where magnetic studies play critical roles in structure determination are considered. This work is supported by the US Department of Energy, Office of FreedomCAR and Fuel Partnership, through the BATT program at Lawrence Berkeley National Laboratory.


PP13.6
Spontaneous Degradation of Ball-Milled Tin(II)-Containing Fluoride Ion Conductor on Aging. Georges Denes, M. Cecilia Madamba and Abdualhafed Muntasar; Chemistry and Biochemistry, Concordia University, Montreal, Quebec, Canada.

For a long time, the best fluoride ion conductors were those crystallizing in the MF2 fluorite type (CaF2 type). This was explained by the presence of empty 0F8 cubes ([0 = vacancy), that can be used as interstitial sites for fluoride ions, tout make a Frenkel defect type of conduction. However, this theory does not explain why the conductivity of beta-PbF2 is much higher than that of BaF2, and why alpha-SnF2 has a conductivity higher than beta-PbF2, even though it has no obvious sites than can be used to form fluoride ion interstitials. Later derivatives of fluorite-type MF2 and SnF2 that have a structure related to the fluorite were found to have much higher conductivities. The case of MSnF4 (M = Ba and Pb) is striking since their conductivity is three orders of magnitude higher than that of the corresponding MF2, with an ionic conduction rate still above 0.99. More recently, we have found that all the MF2/SnF2 compounds can be ball-milled to give fully disordered cubic fluorite-type phases that have lost all evidence of M/Sn order (i.e. the superstructures have disappeared) and of lattice distortion (peak splitting has disappeared). In addition, these phases are nanocrystalline and have a molecular volume larger than the starting ordered phase. It is expected that the extra space can make it easier for the fluoride ions to move when an electric field is applied. The cubic nanocrystalline ball-milled phases are in a metastable state and can be expected to return more or less slowly to a more stable lower energy state, that will likely be more compact, and will probably be less conducting. Degradation of these ball-milled phases, i.e. a phase change to return back to the starting phase, or more often to another phase, has been observed to take place in the following conditions: (i) very rapidly when stirred in water, (ii) very rapidly when annealed above a critical temperature, and (iii) very slowly spontaneously on aging at ambient conditions (over several years).


 

SESSION PP14: Poster Session: Theory
Chair: Richard Dronskowski
Thursday Evening, December 4, 2008
8:00 PM
Exhibition Hall D (Hynes)


PP14.1
Optimization of Transport Properties in AlSb from First Principles Calculations. Daniel Aberg, Paul Erhart, Kuang Jen Wu and Vincenzo Lordi; Lawrence Livermore National Laboratory, Livermore, California.

Aluminum antimonide is a promising material for high-resolution room-temperature radiation detection due to its indirect band gap of 1.6 eV, large average atomic mass, and potential for high electron and hole mobilities. However, achievement of ultimate performance has been hindered by defects. We present a theoretical assessment of defects and impurities in AlSb, related to their effects on carrier mobility and lifetime, and demonstrate experimental improvement in melt-grown bulk material using the theoretical results. All native defects and 10 different impurities were considered, based on those most prevalent in experimental material measured by SIMS. The Al interstitial Ali1+, the Sb antisite SbAl1+, and the Al vacancy VAl3- are identified as the most important intrinsic defects. Using a self-consistent scheme to enforce charge neutrality, we find that the material is intrinsically n-type, despite grown material often exhibiting p-type behavior from unintentional C doping. The theoretical results show that group IV elements substitute for Sb and behave as acceptors, except for Sn which is amphoteric. Group VI elements also substitute for Sb, but behave as donors, with the exception of O. Oxygen is incorporated as an interstitial and acts as an acceptor, according to our calculations. For all impurities considered, the carrier scattering cross section decreases with increasing atomic mass, therefore Te and Se emerge as the most favorable candidates for compensating unintentional p-type doping. Oxygen acts as severe mobility killer. By modifying the growth process to reduce O content and incorporate Te as a compensating dopant, we have achieved simultaneously high mobility and high resistivity material. Finally, we carried out electronic structure calculations to determine the effects of Auger and Schottky-Read-Hall recombination processes, to establish fundamental limits for the carrier lifetimes. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.


PP14.2
Theoretical Study of Strain Effects on ELNES and Electronic Structure of AlGaN. David Holec1, Michal Petrov2, Liverios Lymperakis2, Colin J Humphreys1 and Jörg Neugebauer2; 1Dept. of Materials Science and Metallurgy, University of Cambridge, Cambridge, United Kingdom; 2Max-Planck Institut für Eisenforschung GmbH, Düsseldorf, Germany.

Wurtzite AlGaN is a wide band gap semiconductor alloy of great importance for optoelectronic devices such as light diodes emitting in the UV range or short wave-length laser diodes, both incorporating GaN/AlGaN epitaxial multilayers. Due to different lattice constants of AlN and GaN, the heteroepitaxy leads to either strained (unrelaxed) layers, fully relaxed layers or most often partially relaxed layers (the latter two being defective). As a consequence, the active regions of the devices consisting of several thin layers with varying Al fraction are often under either tensile or compressive strain (depending on a particular device design). Electron energy loss spectroscopy (EELS) performed in a transmission electron microscope offers high spatial (below 1nm) and energy (below 0.1eV with state-of-the-art monochromators) resolution. Its subset, electron energy loss near edge structure (ELNES) is known to reflect the electronic structure of materials. The effect of strain on the N K-edge of ELNES have been reported for InGaN alloys by Keast et al. (J. of Microscopy 210, 89 (2003): Strain may enhance the effects of N K-edge evolution due to changing In concentration, indicating that ELNES may provide an alternative method to lattice imaging to determine the presence of strain. Although there is a large number of experimental and theoretical works which report on the ELNES of N K-edge in AlN, GaN and/or AlGaN, none of them mentions the effect of strain which is almost certainly present in the experimental epitaxial samples. Therefore we have performed plane wave pseudopotential calculations within the density functional theory (DFT) on AlN, GaN and their pseudobinary AlGaN alloys. Based on our calculations we investigated the strain effects on the site and angular momentum projected density of states (PDOS) for several deformation modes and alloy compositions. Biaxial, uniaxial, as well as hydrostatic deformation modes have been assumed and their influence on the N K-edge spectra has been explored. Based on the PDOS we calculated the actual ELNES for some special cases with implications drawn for experimental measurements of ELNES. Subsequently, the changes in the PDOS and ELNES due to strain are linked to variations in the electronic structure. Finally, we discuss how the various deformation modes affect the band structure and the band gap.


PP14.3
Modelling the Crystal Structure of Bi4Ti3O12. Haiming Lu1, Dave Parfitt1, Simon Phillpot3, David R Clark2 and Robin Grimes1; 1Materials, Imperial College, London, United Kingdom; 2Materials, University of California, Santa Barbara, California; 3Material Science and Engineering, University of Florida, Florida, Florida.

Classical molecular dynamics (MD) and density functional theory (DFT) simulations have been employed to investigate the structure of the three-layer Aurivillius phase Bi4Ti3O12, over a range of temperatures. Our particular interest is to investigate the low temperature structure and the existence of intermediate structures during the ferroelectric-para electric transition. The DFT and low temperature MD results show the cell angle is 90.04 and 90.05 respectively matching the experiment results, which suggest a monoclinic structure. However, DFT calculations suggest very small energy differences as a function of the monoclinic angle, resulting in a broad minimum in energy.


PP14.4
A Comparison of Computational Methods that Predict Energies and Structures of Mixed Calcium Strontium Fluorapatites. Emily M Michie1, Eleanor Elizabeth Jay1, Robin W Grimes1, Shirley K Fong2 and Brian Metcalfe2; 1Materials, Imperial College London, London, United Kingdom; 2Material Science Research Division, AWE, Aldermaston, Berkshire, United Kingdom.

Atomic scale local density functional and classical potential simulations, in conjunction with configurational averaging have been used to predict the energies and lattice parameters associated with mixed calcium/strontium fluorapatites, CaxSr10-x(PO4)6F2. In particular, the preference that a Sr2+ ion exhibits to occupy a 6h rather than a 4f cation site has been determined. This is used to establish the occupancy of 6h and 4f sites across the entire compositional range. The internal energy of mixing predicted by the local density functional simulations are in closer agreement with experimental data and exhibit a decidedly less symmetric variation as a function of Ca2+/Sr2+ content than are results generated using the pair potential model. Variations in lattice parameters and lattice volume are also reported as a function of cation content and again differences are apparent.


PP14.5
Predicted Energies and Structures of β-Ca3(PO4)2. Emily Michie1, David Parfitt1, Robin W Grimes1 and Shirley K Fong2; 1Materials, Imperial College London, London, United Kingdom; 2Material Science Research Division, AWE, Aldermaston, Berkshire, United Kingdom.

Atomistic scale computer simulation is used to examine the β-Ca3(PO4)2 structure. Static lattice calculations using classical energy minimization are performed with the GULP code. The Buckingham potential describes the short range interactions between ions with Morse and three body potentials applied to (PO4)3- groups [1]. One of the 6a cation sites of the β-Ca3(PO4)2 structure has previously been assigned half occupancy from fitting to experimental data [2]. Conversely, there are a number of different ways to arrange Ca2+ ions on this 6a site, giving rise to a series of unique ordered arrangements. Alternatively we can use a mean field average occupancy. A comparison of different models is reported, in terms of energy and structure. The most stable arrangement identified gives rise to a lower symmetry space group than reported in literature, R3 rather than R3c. We compare simulated x-ray diffraction patterns of the lowest energy configuration to the average presently accepted and discuss the differences. The reasons as to why the most stable structure should dominate the material is analysed. The stability of the most stable structure over other possible arrangements is analysed in terms of coulomb interactions and lattice relaxations. [1] D. Mkhonto and N.H. de Leeuw; Journal of Materials Chemistry, 12 (9) 2633-2642, 2002 [2] M. Yashima, A. Sakai, T. Kamiyama, A. Hoshikawa; Journal of Solid State Chemistry, 175 (2003) p272-277


PP14.6
Phase Equilibria at Pt-HfO2 Interfaces from first Principles Thermodynamics. Hong Zhu and Rampi Ramprasad; Department of Chemical, Materials and Biomolecular Engineering, Institute of Materials Science, University of Connecticut, Storrs, Connecticut.

Interfaces between metals and metal oxides (such as hafnia, zirconia, etc.) are relevant within the context of electronic devices, fuel cells, batteries, etc. For instance, next generation electronic devices will use a HfO2 based dielectric layer (instead of the currently used silica layer), and a metal gate on top of HfO2 (instead of polycrystalline Si). The choice of the metal on top of HfO2 is determined by the metal work function (i.e., the alignment of the metal Fermi level with the band edges of the Si substrate beneath hafnia). There is very strong evidence that the shifts in the metal work function occurs depending on the morphology of the metal:HfO2 interface. Thus, controlling the interface structure and morphology is seen as an approach to controlling the performance of future electronic devices based on these new materials. We have performed computations based on density functional theory and statistical thermodynamics to study the phase equilibria and atomic level morphology at Pt-HfO2 interfaces as a function of oxygen chemical potential and temperature. Using the “abrupt” interface containing 1 monolayer (ML) of O at the interface as the reference, O-deficient and O-rich situations (spanning 0-2ML) were considered. Based on the total energy of the system for the range of interfacial O coverage obtained from DFT calculations, the probability of a given interfacial O coverage as a function of the O chemical potential was determined. In addition to the expected result that low (high) O chemical potential leads to O-deficient (O-rich, or oxidized) interfaces, our work shows that at temperatures and O pressure values corresponding to typical experimental deposition conditions, several values of interfacial O coverage are equally probably, implying a “rough” interface. Our work provides a technique for directly relating the results of first principles computations to experimental processing conditions, and thus offers a method for guiding the creation of desired interface morphologies.


PP14.7
Surface Structures of Mg/Ag(001): Surface Segregation and Intermixture. Ji-Hwan Kwon1, Jin-Nam Yeo2, Miyoung Kim1 and Byung Deok Yu2; 1Materials Science and Engineering, Seoul National University, Seoul, South Korea; 2Physics, University of Seoul, Seoul, South Korea.

Formation of ultrathin oxide films on metal substrates has attracted a great deal of interest due to their role in applications for catalysis, gas sensors, protective coatings, and electronic devices. In particular, the electrically conductive nature of the metal-supported oxide films allows investigations with various modern experimental techniques that were inhibited by charging effects typical of insulating oxide surfaces. In contrast to surfaces of thicker or bulk-like oxides, the ultrathin oxide films have been found to exhibit more diverse chemical properties for metal adsorbates. Despite these extensive studies, basic mechanisms underlying the formation of the ultrathin oxide films on metal substrates have remained uncertain. In this work, we chose MgO/Ag(001), as a prototypical ultrathin oxide example, that is commonly used to study the properties of metal nanoclusters [1]. By employing ab initio electronic structure calculations based on the density functional theory, we studied the adsorption, formation, and structural properties of Mg atoms on Ag(001) as initial stages of the formation of MgO on Ag(001). The adsorption of a single Mg atom on Ag(001) surfaces was first investigated. Our calculations showed that the Mg atom is substitutionally incorporated into Ag substrates. Furthermore, we also examined the formation and structural properties of Ag(001) with additional Mg atoms by calculating free energies as a function of the Mg chemical potential. Interestingly, the free energy calculations in this study showed that the surface segregation of Ag and the intermixing of Mg and Ag favorably happen. These results provide fundamental and important information to understand very initial stages of the formation procedures of thin oxide films on metal substrates, including oxidation of predeposited Mg films and deposition of Mg in an oxygen atmosphere. We gratefully acknowledge support from the KOSEF through the Basic Research Program under Grant No. R01-2007-000-20249 (B.D.Y.). [1] H.-J. Frend, Surf. Sci. 601, 1438 (2007).


PP14.8
Theoretical Investigation of the Vibrational Properties of BeH2 and Li2BeH4. Hakim Iddir and Peter Zapol; Materials Science Division, Argonne National Laboratory, Argonne, Illinois.

Beryllium hydride, BeH2, exhibits one of the highest hydrogen-to-metal mass ratio (more than 18 wt.%) and presents great fundamental and technological interest as a potential candidate for nuclear industry, energy-conversion devices, rocket propellant, hydrogen storage material. Doping with other light elements, e.g. Li, to keep the compound’s weight low, could be a possible way to decrease the hydride decomposition temperature to a practically acceptable value. An understanding of Li doping effect on the beryllium - hydrogen interaction is a logical way to investigate and design prospective hydrogen storage materials. First principles modeling of BeH2 and Li2BeH4 was performed using density functional theory. The crystal structure (P21/c space group) of Li2BeH4 contains BeH4 tetrahedral units similar to those in BeH2 (body-centered orthorhombic α-BeH2, <it>Ibam2BeH4. Electronic density of states shows considerable differences for the two compounds. The theoretical investigation provided a better understanding of the nature of the bonding in these materials as well as a clear determination of the major vibrational modes contributing to the phonon spectra. This work is supported by the U.S. Department of Energy under Contract No. DE-AC02-06CH11357.


PP14.9
Structural and Vibrational Studies of Nanoporous Silicon. A Novel Approach Using the Tersoff Interatomic Potential. Juan Carlos Noyola1, Alexander Valladares2, R. M Valladares2 and Ariel A. Valladares1; 1Materia Condensada, Instituto de Investigaciones en Materiales, UNAM, Mexico, D.F., Mexico; 2Departamento de Fisica, Facultad de Ciencias, UNAM, Mexico, D.F., Mexico.

Nanoporous silicon periodic supercells with 1000 atoms and 50 % porosity were constructed using the Tersoff interatomic potential and our novel approach [1]. The approach consists in constructing a crystalline diamond-like supercell with a density (volume) close to the real value, then halving the density by doubling the volume, and subjecting the resulting periodic supercell to Tersoff-based molecular dynamics processes at a temperature of 300 K, followed by geometry relaxation. As in the ab initio approach presented in [1] the resulting samples are also essentially amorphous and display pores along some of the “crystallographic” directions. We report the radial (pair) distribution function (RDF) and the pore structure where prominent. We also report a computational prediction for the vibrational density of states for this structure and compare it to the corresponding crystalline one. [1] Computer modeling of nanoporous materials : An ab initio novel approach for silicon and carbon, Ariel A. Valladares, Alexander Valladares and R. M. Valladares, Mater. Res. Soc. Symp. Proc. (2007) Simposyum QQ. Accepted.


PP14.10
Transition Metal Content and its Role in Petroleum Asphaltenes. Olienka Patricia De la O and Russell R Chianelli; Materials Research Institute, University of Texas at El Paso, El Paso, Texas.

Environmental concern has led to increasingly drastic regulations on sulfur, nitrogen and transition metal content in fuels. Sulfur content in the motor and diesel fuels is continuously reduced by regulations to lower levels. The current specification in Europe and USA calls for maximum sulfur content of 50 ppm in gasoline and diesel by 2005, and this level will be reduced to below 10 ppm by 2010. The asphaltenes are not used in its vast potential in the refinery process, in the conversion to lighter fractions of the crude, due to its high content of contaminants; like metals, sulfur and nitrogen. Even they can be converted with great difficulty and expense by addition of hydrogen at high temperature and pressure or they can be destroyed by coking, they present a disposal problem. Asphaltenes are complex mixtures of polyaromatic molecules and are thought to be the remains of biological molecules from which petroleum was formed. Therefore they contain metals like vanadium and nickel in porphyrinic ring-like structures reminiscent of biological molecules. Transition Metal (TM) catalysts play an important role in the petroleum industry. Due to their resistance to poisons, these catalysts are important for the removal of heteroatoms (N, S, O) in the presence of large amounts of hydrogen. The need to meet more stringent standards limiting the TM content of crude oils urges a deeper understanding of the different structures that is composed like asphaltenes and the mechanisms to reduce that metal content (catalysts). In order to understand the behavior and crystalline structure of Asphaltenes it is realized Molecular simulations through Density Functional Theory, under Gaussian, Cerius2, Materials Studio softwares designed to visualize structures, predict the properties and behavior of chemical systems, refine structural models, and modify the synthesis process to improve and to adapt the structures to specific necessities very important in the creation or regeneration of sources of energy that could satisfied the world consume avoiding the contamination factor, crucial in the green energy generation.


PP14.11
Morphological Evolution of Hydrated Phases and their Relation with Molar Concentrations of Interstitial Solution in Cement and Concrete. Nicanor Rubiera Prendes, Esperanza M Menendez and Ignacio Echegoyen; Geology, Public Work Ministry, Madrid, Madrid, Spain.

Hydration, as a result of physical and chemical reactions between water and anhydrous phases, generates a series of mechanically resistant microstructures whose crystallochemical properties are ruled by the solute’s conditions. The results are a series of crystalline phases which conform a porous network, which is “refill” as hydration progresses and in which liquid phases are concentrated in micropores. The presence of some of these minerals, at different ages and with different morphologies, provides very valuable information about the texturization kinetics and the hydrated product characteristics. Using the ideas of D’Ans, J. et Pick, H. & Mehta, P. K., as web as the works of Bentz, D. & Zinder, K.A. as a starting point, and making use of Scanning Electron Microscopy (SEM), in secondary electron detection mode, a ‘paragenesis’ - or sequences of formation of mineral phases - has been proposed for cement and concrete, which can explain the ‘chemical mismatches’ that occur in certain mortars and that are associated to cement or concrete pathologies. The theoretical approach is therefore very simple. Starting from phase equilibrium diagrams, which define the molecular concentrations of these compounds, their fields of existence are delimited (ettringites, portlandites, etc) and their previous salinity conditions are deduced (pH, molar concentrations, etc), as well as the formation sequence for those specific variables (as follows from percolation theory and critical degree of hydration, according to the criteria experimentally established by Sohn, D.). The proposed development is an evolution - and interaction - between current systems, which lean towards an equilibrium conditions in which the hardening and solidification of the paste must be achieved. In the case of mismatches and variations (frequently associated to the reticular complexity of silicates) the degree and type of hydrations is altered, therefore favoring the development of phases that can be considered ‘anomalous’, such as ‘Delayed ettringites’, portlandites concentrations or the appearance of tobermoritic compounds. Thus, ettringite would always be formed - under normal conditions - during the first stages of hydration and in those when during its growth, given some ‘high plasticity’ conditions, its disruptive tensions were to be absorbed; but if, because of processes associated to pH or molar concentration (μ) variations, ettringite were to be formed during the late stages (under rigidity conditions), tensional development and the appearance of pathologies (micro fissures) would be favored. The morphological development of these phases is, therefore, a structural and crystallochemical stability criterion. As a result, the growth of portlandite crystals which develop in prismatic habits, or the presence of acicular ettringite crystals, define a certain set of local textured of hydration products, apart from their temperature, molar concentration, and microporous structure.


 

SESSION PP15: Characterization of Complex Structures
Chairs: Peter Chupas and John Evans
Friday Morning, December 5, 2008
Back Bay C (Sheraton)


8:30 AM *PP15.1
Advanced Nitrides and Neutrons: New Nitridic Itinerant Ferromagnets and the High-Performance Time-of-Flight Neutron Diffractometer POWTEX. Richard Vinzenz Dronskowski and Andreas Houben; Institute of Inorganic Chemistry, RWTH Aachen University, Aachen, NRW, Germany.

The last decade has witnessed an unprecedented increase in magnetic data storage, not necessarily by the miniaturization of components, but through the application of novel physical phenomena, e.g., giant magnetoresistance. Sooner or later, however, magnetic data storage and the thus defined “digital age” will face up to the problem of the superparamagnetic limit. Solid-state chemistry can play a major role in postponing the latter problem by making novel storage technologies possible, for example through the synthesis of exceptionally hard ferromagnetic materials used as advanced recording heads. Inspired by the existence of the known ferromagnetic nitride Fe4N, electronic-structure calculations of density-functional type have turned out extremely useful for the prediction and rational design of superior ternary and, also, quaternary nitrides adopting the same perovskite-like crystal structure. The new phase RhFe3N, for example, also exhibits a high saturation magnetization, but combined with a much lower coercive field, which makes it an ideal candidate for above-mentioned recording heads. A further improvement of the physical properties can be accomplished by the partial or complete substitution of Rh against Co, Ni, Ru, and Pd. These berthollide materials, however, are difficult to characterize using X-ray diffraction due to the similar scattering factors of, say, Fe, Co, and Ni, but also those of Rh and Ru. Above analytical problems clearly demand neutron diffraction experiments. In order to provide the German and international chemistry and materials-science communities with the most powerful tool for rapid neutron-data acquisition, the novel time-of-flight diffractometer POWTEX will be installed at the new FRM II reactor at Munich. The POWTEX machine, a collaboration between RWTH Aachen University, Forschungszentrum Jülich, Göttingen University and the Technical University of Munich, is expected to outperform comparable monochromator instruments by one order of magnitude in intensity (> 3 × 10^7 neutrons/cm2s) for small samples of less than a cubic centimeter. The technical design of POWTEX utilizes modern neutron components such as focusing super-mirror neutron guides, a four-unit high-speed disk-chopper system, and linear position-sensitive detectors covering a solid angle of about 5.2 steradian. While POWTEX is under construction at the very moment, we expect to conduct the first measurements in the year 2012.


9:00 AM PP15.2
Characterization of Subtle Framework Distortions using Solid-state NMR and First Principles Calculation. Anne Soleilhavoup, John Evans and Paul Hodgkinson; Department of Chemistry, Durham University, Durham, United Kingdom.

Solid-state NMR is a powerful tool for probing local structural environment and dynamic behavior in a wide variety of solid materials. We have shown, for example, how 17O NMR, in combination with diffraction measurements, can be used to characterize oxygen dynamics in the negative thermal expansion material α-zirconium tungstate1. The characterization of dynamics via NMR is relatively straightforward since there are simple, direct relationships between the dynamic behavior and its effect on the different NMR parameters (such as relaxation times). In contrast, the connections between structure and NMR parameters is much less direct; for example, chemical shifts are extremely sensitive to subtle variations in local environment, but it is not feasible to infer structure directly from NMR measurements. Recent developments in first principles calculation mean, however, that NMR parameters can now be calculated relatively straightforwardly, for a given structural model, using DFT-based techniques that use plane-wave basis sets to describe the bonding electrons in periodically repeating i.e. crystalline structures. Codes, such as CASTEP, provide a vital link between structure and NMR observables. We show how 17O NMR provides direct information on the nature of the oxygen environments in different phases of zirconium tungstate2, including the material obtained by pressure-induced amorphization; information that can be readily incorporated into structural modeling. DFT calculations are also used to connect the subtle temperature dependence of the 17O chemical shifts of the normal α phase to structural models of vibrational averaging deduced from total scattering studies. 17O NMR has also proved invaluable in characterizing the subtle series of framework distortions undergone by tungsten oxide as a function of temperature. Using DFT calculations, we can determine how different distortions of the WO6 octahedra affect NMR parameters such as the 17O chemical shift and quadrupole coupling. Hence NMR parameters can be linked to structure in a much more direct and fundamental fashion than is possible from traditional approaches. It is found that the NMR spectra are sensitive to picometre structural distortions within the error limits set on diffraction-derived structures set by the modeling of diffraction peak shapes. 1. M. R. Hampson, J. S. O. Evans and P. Hodgkinson, J. Am. Chem. Soc. 127 15175 (2005) 2. A. Soleilhavoup, M. R. Hampson, S. J. Clark, J. S. O. Evans and P. Hodgkinson, Magn. Reson. Chem. 45 S144 (2007)


9:15 AM PP15.3
Structure Determination of Modulated Structures in the γ-Brass System Through a (3+1)-dimensional Space Description. Olivier Gourdon1 and Gordon Miller2; 1ORNL, Oak Ridge, Tennessee; 2Iowa State University, AMes, Iowa.

Our investigations in the γ-brass system are related to the idea that a prototypic 1-dimensional (1D) quasicrystal, as defined by the Fibonacci sequence, can be regarded both as a quasicrystal and as an incommensurately modulated crystal. Consequently, there are two different ways to achieve the atomic structure. Six different new structures, closely related to the γ-brass structure, in the Zn1[|#1#|]xPdx system have been synthesized. A misfit character of all structures with two distinct main subsets and satellite reflections is clear from the diffraction patterns. Among these structures, two specific examples, Zn10.65Pd2.35 (Zn0.819Pd0.181) and Zn212Pd64 (Zn0.768Pd0.232), have been refined by single crystal X-ray diffraction using traditional refinement methods but also usingthe (3+1)D formalism (superspace group Xmmm(00γ)0s0). Analogies with the Fibonacci sequence are possible if we identify dimers of Pd-centred Zn icosahedra (DI) as short segments, S, and trimers of Pd-centred Zn icosahedra (TI) as long segments, L. By defining these S and L segments, Zn11Pd2 and Zn212Pd64 correspond to the two first simplest approximants of a hypothetical 1D quasicrystal.


9:30 AM PP15.4
Abstract Withdrawn


9:45 AM PP15.5
Nanocomposite Formation on AAMMO6 Perovskites. A Transmission Electron Microscopy Study. Susana Garcia-Martin1, Esteban Urones-Garrote1, Meghan Knapp2, Graham King2 and Patrick Woodward2; 1Department of Inorganic Chemistry, Faculty of Chemistry, Complutense University, Madrid, Spain; 2Department of Chemistry, The Ohio State University, Columbus, Ohio.

The properties of complex AAMMO6 perovskites can be highly sensitive to order/disorder effects of the cation sublattices. M-site cation ordering (usually rock salt-type) is more common than A-site cation ordering, which generally consist of a layered arrangement and it is often found in combination with anion vacancies, A-site cation vacancies or pronounced octahedral tilting distortions. Examples where both cation sublattices order are rare. Thus it is significant that we have been able to prepare a number of new quintinary stoichiometric perovskites which present both A and M-site cation ordering (1, 2). Interestingly, some of them show intriguing complexities in their neutron diffraction patterns probably related to the crystal microstructure of these compounds. Powder X-ray and neutron diffraction techniques probe the average structure of these solids. Small deviations from an average structure such as short range ordering of cations are very difficult to detect by these techniques. However, electron diffraction and transmission electron microscopy are powerful methods which provide complementary information for studying the crystal structure of the materials, especially certain defect structures. We have studied the crystal microstructure of some AAMMO6 perovskites by Selected Area Electron Diffraction (SAED), High Resolution Transmission Electron Microscopy (HRTEM), and Scanning TEM-Electron Energy-Loss Spectroscopy (STEM-EELS). We find spontaneous phase separation to form ordered nanocomposite superlattices in NaLaMgWO6. Similar features are found in other substitutional derivatives of this structure. This compositional modulation of the crystal structure will undoubtedly impact the physical properties of these oxides. Their behaviour can resemble that of materials made from layer by layer growth of two dimensional thin film perovskite heterostructures, which can present attractive dielectric, magnetic and/or ionic conductivity properties. 1. Knapp, M. C.; Woodward, P. M. J. Solid State Chem. 2006, 179, 1076. 2. King, G.; Thimmaiah, S.; Dwivedi, A.; Woodward, P. M. Chem. Mater. 2007, 19, 6451.


10:30 AM PP15.6
Persistent Tetragonality at High Temperature in Ferroelectric Perovskites. David Michael Stein and Peter K Davies; Materials Science & Engineering, University of Pennsylvania, Philadelphia, Pennsylvania.

Environmental regulations dictate the need for reducing or eliminating lead content in ferroelectric and piezoelectric applications. Substitution of bismuth for the lead cations and specific coordinating B-site cations into the ferroelectric perovskite lead titanate (PT) has produced promising solid-solution systems with tunable Curie temperatures and tetragonality in excess of the PT end-member. Capturing these enhanced properties for piezoelectric applications requires carefully choosing additives that maintain the increased tetragonality while approaching a morphotropic phase boundary (MPB) for maximized piezoelectric properties. In support of this research goal, we present a family of solid solution systems with MPB-forming additives, Bi(Mg1/2Ti1/2)O3 and Bi(Mg1/2Zr1/2)O3, substituted into a tetragonality-enhanced system: PbTiO3-Bi(Zn1/2Ti1/2)O3. These systems exhibit multiple dielectric maxima at temperatures above room temperature, including a high-temperature maximum near 600°C exhibiting the hysteretic behavior common in ferroelectric to paraelectric transitions. Neutron and X-ray diffraction techniques reveal that a typical tetragonal to cubic phase transition is responsible for the lower temperature dielectric maximum, but are unable to resolve a structural symmetry change origin for the high temperature dielectric maximum. However, the hysteretic behavior of that maximum is inconsistent with a purely cubic phase. We will explain the data as an effect of localized clusters of bismuth-rich tetragonal structure that persist to higher temperatures than the surrounding matrix and we will provide indirect thermal expansion evidence for this theory.


10:45 AM PP15.7
The Non-stoichiometry-induced Crystal Chemistry of Perovskite Ba3CoNb2O9. Bostjan Jancar1, Matjaz Spreitzer1, Anatolii Belous3, Oleg Ovchar3, Olexandr Kramarenko3 and Giuseppe Annino2; 1Advanced materials, Jozef Stefan Institute, Ljubljana, Slovenia; 2Istituto per i Processi Chimico-Fisici CNR, Pisa, Italy; 3Solid state chemistry, V.I.Vernadskii Institute of General and Inorganic Chemistry,, Kyiv, Ukraine.

Perovskite materials that exhibit B-site cation order have been attracting the interest of the dielectric-research community for decades. Ceramics based on these are being utilized for the production of the base-station dielectric resonators that are part of the wireless telecommunication networks. It has been established that the degree of cation order is one of the key parameters controlling the dielectric loss of such ceramics. Such a crystal-structure ordering is usually kinetically sluggish and therefore requires extended annealing times. As a consequence majority of the research has been devoted to altering the chemistry of this type of perovskites in such a way to achieve a high degree of cation order within economically acceptable time frame. Lately investigations regarding the introduction of defects into the crystal structure of such perovskites has received much attention. It has been argued that cation vacancies increase the ordering kinetics, however, the literature data ont this matter is scarce and often appears to be contradictory. We have investigated the effect of non-stoichiometry on the formation of the defects in the perovskite Ba3CoNb2O9. The combined electron diffraction and electron -probe microanalysis showed that slight B-site cation deficiency results in a defect perovskite that exhibits a faster kinetics of cation ordering compared to a stoichiometric composition. Furthermore high-resolution phase-contrast electron microscopy has shown that deviation from stoichiometry causes formation of polytypic planar faults that are coherently grown with the perovskite matrix. Such faults are local disruption of cubic close packing that result in face-sharing instead of edge-sharing of BO6 polyhedra. The experiments have shown that such coherent intergrwoths tend to considerably reduce the dielectric loss of the ceramics based on perovskite Ba3CoNb2O9.


11:00 AM PP15.8
EELS Study of Atomic Vacancies and Nitrogen Position in SrTiO3-x:Ny Single Crystal Obtained by Microwave Plasma Ammonolysis. Myriam Haydee Aguirre1, Andrey Shkabko1, Dmitry Logvinovich1, Rosa Robert1, Laura Bocher1, Anke Weidenkaff1, Peng Wang2 and Ursel Bangert3; 1Solid State Chemistry and Catalysis, EMPA, Duebendorf, Switzerland; 2SuperSTEM, Daresbury Laboratory, Daresbury, Cheshire, United Kingdom; 3School of Materials, The University of Manchester, Manchester, United Kingdom.

Perovskite oxides have been the subject of intense research on account of their ferroelectric and dielectric properties, which can be used effectively in a wide range of applications, such as non-volatile ferroelectric and high-density dynamic random access memory devices [1]. Phenomena like 2D-Electron Gas [2] or resistivity switching [3] have been recently discovered in perovskite materials. From the perovskite material knowledge area, the oxynitride-perovskites AB(O,N)3 are a growing class of materials with prospective optical and catalytic properties [4]. One method to introduce nitrogen (N) into SrTiO3 (STO) perovskite structure is by mean of microwave induced NH3 plasma procedure. In this two step treatment, the following modifications of the chemical composition are used to change the electronic structure and properties of STO: i) formation of oxygen vacancies, and ii) an anionic substitution N3- → O2-. Substitution of O2- with N3- in perovskites is possible due to the similar ion size of both elements. However, due to the charge compensating mechanism complete anionic substitution of O2- by N3- keeping the perovskite type structure can not be realized without the presence of anionic vacancies (collapsed in dislocations, stacking faults and new structures or superstructures). With the reduction scaling of microelectronic devices, lattice defects in these materials become increasingly important. Therefore, it is extremely demanding the careful characterization of defects produced during the ammonia plasma treatment. Several questions arise in this work such as the defect type, how the lattice distortion is around the defect, the local change in composition, and where the N is inserted in the structure. High-resolution transmission electron microscopy (HRTEM) is the first essential step for research on lattice defects. But, the distinct composition changes around the defects can be better studied by Z-contrast image and mapped with sub-nanometer spatial resolution utilizing EELS in scanning transmission electron microscopy (STEM). On the basis of collected Ti L2,3, O and N K-line EELS spectra around defect zones and free defect zones, and combined with high resolution HAADF and HRTEM, bonding and composition information will be correlated with the atomic structure of SrTiO3-x:Ny. References [1] N. Setter and R. Waser, Acta Mater. 48 , 151 (2000) [2] Ohtomo A. and Hwang H. Y., Nature, 427 , 423(2004). [3] K. Szot, W. Speier, G. Bihlmayer, et. al. Nat. Mater. 5 , 312 (2006). [4] F. Tessier and R. Marchand, J.Sol. Stat. Chem. 171 , 143(2000).


11:15 AM PP15.9
Imaging of the Profiles of Intrinsic Defects in Cd1-xZnxTe Crystals by Tracer Diffusion Experiments. Thomas Wichert, Joerg Kronenberg, Frank Wagner and Herbert Wolf; Technische Physik, Universitaet des Saarlandes, 66041 Saarbruecken, Saarland, Germany.

The diffusion of the group-I elements Ag and Cu in Cd1-xZnxTe crystals can result in the formation of unusual diffusion profiles that start at a constant low concentration level from the surface and exhibit a peak-shaped increase which is symmetrical with respect to the center of the crystal. This type of diffusion profile is observed after one-sided implantation of the radiotracer 111Ag (67Cu) with 60 keV into typically 800 µm thick crystals and subsequent annealing at 800 K for 60 min under Cd pressure. It turns out that the formation of those diffusion profiles is connected with the depth distribution of intrinsic defects [1,2]. Meanwhile, similar profiles have been observed for Na, but not for K or the group-I element Au. As far as it concerns this investigation, an outstanding feature of the Cd1-xZnxTe systerm is the possibility of forming large deviations from stoichiometry. Since the most prominent intrinsic defects in CdTe are the interstitial Cd atom Cdi and the Cd vacancy VCd the deviation from stoichiometry is well approximated by the quantity [ΔC] = [Cdi] - [VCd]. Thus, at thermal equilibrium at 800 K, the deviation from stoichiometry ranges from [ΔC] = -3×1016 cm-3 in Te saturated vapor to [ΔC] = +2×1015 cm-3 in Cd saturated vapor. Usually, after growth Cd1-xZnxTe crystals exhibit a strongly negative deviation from stoichiometry. Therefore, annealing under Cd pressure, causing a penetration of interstitial Cd atoms from both surfaces into the Cd deficient crystal, creates a transition from Cd rich material ([ΔC] > 0) to Te rich material ([ΔC] < 0) towards the interior of the crystal. Due to the fact that the Cdi and VCd defects act as donors and as acceptors, respectively, this transition constitute a pn junction, as well, propagating from both surfaces into the crystal. The actual position of the pn junction depends on the diffusion coefficient of the more mobile intrinsic defect, which is the Cdi defect in this case, and on the annealing time. In this description, the shape of the dopant profile is completely understandable if the dopant atoms are largely present as interstitially incorporated, positively charged ions with high mobility. Recent tracer diffusion experiments performed with the transition metals Ni and Co yield box shaped profiles which are understandable under the assumption that Ni and Co are highly mobile and are present as negatively charged ions. The financial support of the BMBF under contract 05 KK7TS1 is gratefully acknowledged. [1] H. Wolf, F. Wagner, Th. Wichert, and ISOLDE Collaboration, Phys. Rev. Lett. 94 (2005) 125901. [2] H. Wolf, F. Wagner, Th. Wichert, R. Grill, E. Belas, and ISOLDE collaboration, J. Electr. Mater. 35 (2006) 1350.


11:30 AM PP15.10
Stabilization of Misfit Layer Compounds by Metal Cross Substitution. Hans Starnberg1, Matthias Kallaene2, Kai Rossnagel2, Martin Marczynski-Buehlow2, Sven Stoltz1,3 and Lutz Kipp2; 1Department of Physics, University of Gothenburg, Gothenburg, Sweden; 2Institute for Experimental and Applied Physics, University of Kiel, Kiel, Germany; 3School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts.

Misfit layer compounds, in which layers of cubic monochalcogenides are alternated with layers of hexagonal transition metal dichalcogenides, are characterized by nanoscale modulations along certain directions due the two subsystems being incommensurate. They are remarkably stable, however, despite the deviations from perfect crystalline order, and there has been controversy over the nature of interlayer bonding. We have used spatially resolved photoelectron spectroscopy to study (PbS)1.13TaS2, and found evidence for significant substitution of Pb into TaS2 layers and Ta into PbS layers. This metal cross substitution may be the key to stability for this compound, by causing a bonding charge redistribution between the layers. We have also verified that metal substitution occurs in other misfit layer compounds, and thus may be a general feature for this class of materials. The photoemission experiments were done at MAX-lab, HASYLAB and the ALS, with support from the Swedish Natural Science Research Council and the Deutsche Forschungsgemeinschaft.


11:45 AM PP15.11
A New Application for Old Techniques: Combined Use of X-ray Powder Diffraction and Mössbauer Spectroscopy for the Study of Tin(II)-Containing Ionic Conductors. Georges Denes, M. Cecilia Madamba and Abdualhafed Muntasar; Chemistry and Biochemistry, Concordia University, Montreal, Quebec, Canada.

The highest performance fluoride ion conductors are based on combinations of tin(II) fluoride and a fluorite-type MF2. These have conductivities up to three orders of magnitude higher than that of the parent MF2. The structural characterization of many of these phases is particularly difficult because the diffraction method, is not as powerful as usual, due to (i) reduced crystallinity, high preferred orientation and sometimes high internal strain, in ordered phases, and (ii) disorder in other phases. A judicious combination of X-ray powder diffraction and Mössbauer spectroscopy has made it possible to extract key information about their crystal structure and electronic structure. The knowledge of the latter is particularly useful in order to determine whether electrons can also be mobile, without the need for transport number measurements. Comparison of the X-ray diffraction pattern with that of the fluorite type MF2 shows whether they are related, and how: (i) peak splitting shows the presence of a lattice distortion (tetragonal for α-MSnF4 (M = Sr, Ba and Pb) and orthorhombic for o-PbSnF4); (ii) additional peaks at low angles indicate the probable presence of a superstructure characteristics of M/Sn order); (iii) lack of peak splitting and superstructure peaks show full M/Sn disordered (PbSn4F10, γ-PbSnF4, μγ-MSnF4 (M = Ba and Pb), μγ-Pb2SnF6, M1-xSnxF2 (M = Ca and Pb; (iv) highly intense superstructure peaks with poorly reproducible intensities from one sample to another and indicate high preferred orientation, usually due to clustering of tin(II) lone pairs in sheets. The identification of the direction of preferred orientation, from the peak indexation, has made it possible, using the crystal symmetry, to identify the type of M/Sn order and provide a starting solution that was then used with neutron diffraction data. Full M/Sn disorder raises the question about the tin bonding type and coordination: is bonding at tin ionic with a regular coordination (cubic in the fluorite type structure) like for the M2+ion? Tin-119 Mössbauer spectroscopy is a local probe that provides invaluable information that complements those obtained from diffraction: (a) a tin(II) doublet shows covalent bonding, whereas a single line indicates that bonding at tin is ionic; (b) a strong doublet anisotropy changing with sample orientation results from high preferred orientation and helps identifying the direction of the lone pair axis; (c) a milder doublet anisotropy increasing when temperature is raised shows that bonding is highly anisotropic; (d) the presence of stannic oxide due to surface oxidation is also accomplished by Mössbauer spectroscopy. When bonding is covalent, the tin(II) electron lone pair is locked on hybrid orbital (stereoactive lone pair) and therefore cannot be a charge carrier, while in the case of ionic bonding, it is on the native 5s orbital and can contribute to the total conductivity.

 

AdAd Back To Top

Publishing Partner

Corporate Partners

AdAdAd