Symposium Organizers
P. Shiv Halasyamani University of Houston
David G. Mandrus The University of Tennessee/Oak Ridge National Laboratory
Kyoung-Shin Choi Purdue University
Simon J. Clarke University of Oxford
EE3: Poster Session: Solid State Chemistry of Inorganic Materials VIII
Session Chairs
Tuesday AM, November 30, 2010
Exhibition Hall D (Hynes)
EE1: Novel Synthetic Methods
Session Chairs
P Shiv Halasyamani
Arthur Mar
Monday PM, November 29, 2010
Ballroom A, 3rd floor (Hynes)
9:30 AM - **EE1.1
Fullerene Superconductivity: Alive and Kicking.
Kosmas Prassides 1
1 Chemistry, Durham University, Durham United Kingdom
Show AbstractC60-based solids are archetypal examples of molecular superconductors with Tc as high as 33 K. Tc of the face-centered cubic (fcc) A3C60 (A = alkali metal) fullerides increases monotonically with the interC60 separation, which is in turn controlled by the sizes of the A+ cations – this physical picture has remained unaltered since 1992. Pressure-induced trace superconductivity (s/c fraction<<1%) at ~40 K was reported in 1995 in multiphase samples in the CsxC60 phase field. Despite numerous attempts by many groups worldwide, this remained unverified and the structure and composition of the material responsible for superconductivity unidentified. This has hindered any attempt to push Tc even higher and make contact with theory which predicts correlation-enhanced superconductivity for expanded fullerides near the metal-insulator transition. Here I will present our recent work in this field that led to the discovery of pressure-induced bulk superconductivity emerging out of parent magnetic insulating states in fulleride polymorphic phases at the highest Tc currently known for any molecular material [1,2,3].References[1] A.Y. Ganin et al. Nature Mater. 7, 367 (2008). [2] Y. Takabayashi et al. Science 323, 1585 (2009).[3] A.Y. Ganin et al. Nature, doi:10.1038/nature09120 (2010).
10:00 AM - EE1.2
Novel Phase of Rubidium Superoxide: Oxygen-deficient RbO2-δ.
Syarif Riyadi 1 , Shivakumara Giriyapura 1 , Robert de Groot 1 2 , Thomas Palstra 1 , Graeme Blake 1
1 Solid State Materials for Electronics, University of Groningen, Groningen Netherlands, 2 Electronic Structure of Materials, Radboud University of Nijmegen, Nijmegen Netherlands
Show AbstractAlkali metal superoxides (e.g. NaO2, KO2, RbO2) are among rare oxide materials in which the magnetic properties originate from electrons in the p-shell. In these materials, the superoxide molecule, a dioxygen dumbbell, has one unpaired electron in its π* level. Alkali superoxides are known to undergo multiple structural phase transitions with temperature. In most cases, the structural change involves cooperative reorientation or shifts of the dioxygen dumbbells. A novel oxygen-deficient phase of rubidium superoxide (RbO2-δ) has been synthesized by thermal decomposition of fully-stoichiometric tetragonal RbO2. The crystal structure of RbO2-δ at room temperature is very similar to that of the disordered-pyrite structure of NaO2, where the orientations of the dioxygen dumbbells are disordered but with a preference for the four body-diagonals of the cubic unit cell. Structural studies at low temperature indicate a slow reorientation of the superoxide dumbbells starting around 230 K, below which the orientation of the dumbbells becomes confined to the basal plane of a tetragonal unit cell; the degree of remaining disorder depends on the speed at which the sample is cooled. Magnetization measurements indicate magnetic frustration below ~50 K. We suggest that the superoxide anions are segregated into ferromagnetic and antiferromagnetic clusters, with ferromagnetic interactions dominant at the lowest temperatures. Both ferromagnetic and antiferromagnetic interactions are possible due to the presence of both orthogonal and parallel arrangements of nearest-neighbor oxygen dumbbells.
10:15 AM - EE1.3
Preparation, Physical Properties and Chemical Reactivities of Ambient Pressure and High Pressure Oxide Phases.
Mario Bieringer 1 , Miguel Alario Franco 2
1 Chemistry, University of Manitoba, Winnipeg, Manitoba, Canada, 2 Departamento de Quimica Inorganica I, Universidad Complutense, Madrid Spain
Show AbstractUnderstanding solid state reaction pathways provides important insights for the rational design of new extended solid state materials. We are investigating the formation of oxide phases in real time using in situ diffraction methods and have placed particular emphasis on the exploration of metastable intermediates that can be accessed by topotactic reactions. Novel phases with excellent control of oxidation states, oxide defect concentrations and oxide ordering have been discovered. In addition high pressure synthesis gives access to the formation of metastable high density structures that can be contrasted with the ambient structure equivalents. These phases show very distinct physical properties and also allow probing our structure-reactivity relationships. We can now control the solid state reactivity of these phases leading to ordered or disordered products. Particularly intriguing is a system of vanadates and titanates that provides ample of opportunities for the targeted synthesis of novel oxide structures. Rich phase diagrams and reactivity schemes have resulted from these systems. Topotactic reduction and oxidation pathways will be illustrated and the very diverse physical properties as well as magnetic structures of these systems will be the focus of this discussion.
10:30 AM - EE1.4
Superconducting Parent Compound Pr2CuO4 Achieved by Special Post-reduction.
Hideki Yamamoto 1 , Osamu Matsumoto 2 , Keitaro Yamagami 1 , Michio Naito 2 , Yoshiharu Krockenberger 1
1 , NTT Basic Research Labs., NTT Corporation, Atsugi-shi Japan, 2 , Tokyo Univ. of Agriculture and Technology, Koganei-shi Japan
Show AbstractIt is commonly believed that the parent compounds of high-Tc cupratres are universally Mott insulators. In our experiments using metal-organic decomposition (MOD), however, accumulating evidences show that the parent compounds of “electron-doped” superconductors, RE2-xCexCuO4 [RE = rare earth element] with x = 0, are not Mott insulators but superconductors [1]. They have Tc of 30 K and crystallize in the Nd2CuO4 (T’) structure. Most likely, the sharp contradiction between our results and commonly achieved data originates from the complicated oxygen chemistry in these materials. The as-synthesized specimens contain a fair amount of impurity interstitial oxygen. Throughout the reduction process it is inherent to remove exclusively impurity oxygen while preserving regular oxygen site occupied in order to obtain superconductivity. More stringent reduction control is necessary with decreasing x to fulfill this requirement. In this study, we systematically investigated the post-reduction process using MBE-grown T’-Pr2CuO4 films. The aim is to establish a synthesis route to the parent compound superconductors other than MOD. The MBE films were reduced ex-situ in a tubular furnace following a specially designed 2-step process, as in the case of MOD films. The films were annealed at Ta = 700 - 850°C in a reducing atmosphere (PO2 = 2 x 10-5–2 x 10-3 atm) and finally reduced at a lower temperature Tred = 450 – 700°C under vacuum (< 10-4 Torr). The film properties systematically changed with Ta, PO2, and Tred. The optimized Tred varies from 475°C to 650°C mainly depending on Ta. This is most likely since the microstructure and grain size of the films are determined by Ta, judging from AFM observation. Optimal superconducting properties are Tc of 26-27 K, while ρ(300 K) = 250μΩcm, and RRR ~ 10. We believe the combination of thin-film synthesis and specially designed post-reduction process enabled us to obtain nearly intact CuO2 planes. Samples prepared by above-mentioned method unveiled the intrinsic properties of the parent compounds, which are not Mott insulators. This result also agrees with the recent calculation result indicating the parent compounds with T’ structure are not Mott insulators[2].[1] O. Matsumoto et al., Phys. Rev. B 79 (2009) 100508(R); Physica C 469 (2009) 924.[2] C. Weber, K. Haule, G. Kotliar, arXiv: 1005.3095; arXiv: 1005.3100.
11:15 AM - **EE1.5
The Utility of Salt-inclusion Chemistry in the Formation of Water-soluble Solids Comprised of High Nuclearity Transition-metal Oxide Clusters.
Wendy Queen 1 , Jennings West 1 , Trent Anderson 2 , Matthew Dunlap 1 , Shiou-Jyh Hwu 1
1 Chemistry, Clemson Uninversity, Clemson, South Carolina, United States, 2 Chemistry, Augustana College, Rock Island, Illinois, United States
Show AbstractTransition metal oxide (TMO) clusters, also known as polyoxometalates (POMs), offer an assortment of different structural motifs that serve as molecular like building blocks for extended solids. Prior to this report, POMs have been synthesized using a variety of different methods such as hydrolytic aggregation in non-aqueous media, conventional hydrothermal or solvothermal techniques, and reductive aggregation processes. Using salt inclusion chemistry, a new class of polyoxovanadate (POV) containing materials was discovered. This is the first time these aggregates have resulted from a high temperature technique (T > 500°C), and their water solubility can allow further chemical manipulation in aqueous media.Recent reports have highlighted the inclusion of active halide fluxes (molten salt) as a structure-directing agent to synthesize low-dimensional solids that contain nanostructured metal-oxide lattices. Although no reaction mechanism is known, one can imagine that the metal oxides are first “dissolved” in the corrosive molten salt and then, upon cooling, the covalent lattice begins to aggregate within and/or around the inherent structure of the molten ionic salt, resulting in the formation of special frameworks. These all-inorganic salt-inclusion solids (SISs) possess a fascinating structural chemistry where bonding at the interface of the dissimilar components appears to be directional. This property has been revealed through the formation of salt-templated porous frameworks, noncentrosymmetric (NCS) lattices, and now for the first time, magnetic metal-oxide clusters.Here we will report the synthesis and characterization of a fascinating family of hybrid materials containing high nuclearity vanadium oxide clusters. The four new compounds to be discussed have been investigated using single-crystal X-ray diffraction and their structural compositions are Cs11Na3(V15O36)Cl6 (1), Cs5(V14O22)(As2O5)4Cl (X = Cl, Br, I) (2a∼c), Cs5(V14As8O42X)●1.5 H2O (X = Br or I) (3a,b), and Cs5(V14O34)(AsO3)2Cl●2.6H2O (4), respectively. Compounds 1 and 2 were synthesized using high-temperature methods in molten-salt media while 3 and 4 were controllably formed after the dissolution of 2. These new SISs contain polyoxometallate cores with the compositions [V15O36Cl]9− (1), [V14As8O42X]5− (2a and 3a,b), and [V14As2O40Cl]5− (4). In this presentation, we will also address its utility as a synthone for the synthesis of porous solids comprised of high nuclearity POV clusters as a charge reservoir for redox intercalation.
11:45 AM - EE1.6
Controlled Hydrothermal Synthesis of Complex Mixed Oxides Using Solution Redox Chemistry.
Richard Walton 1 , Kripasindu Sardar 1 , Deena Modeshia 1 , Craig Hilley 1
1 Department of Chemistry, University of Warwick, Coventry United Kingdom
Show AbstractHydrothermal synthesis has proved already to be a versatile method for the synthesis of a variety of transition-metal oxides, including important members of the perovskite family such as BaTiO3, PZT, NaNbO3 and Ln1-xAxMnO3. It provides a low-temperature single-step synthesis of fine powders of functional materials without the need for any post-synthesis annealing and in some cases with control of crystal morphology on the nanoscale.[1-3] In this presentation I will report our recent results in an investigation of the scope of the hydrothermal method in the synthesis of more complex oxide systems, where the control of the metal oxidation state is important in dictating their properties. The aqueous solutions used in synthesis provide a convenient means for the inclusion of oxidising or reducing agents to permit the control of metal oxidation state in the final product. Some new examples of this approach to synthesis will be described.Reaction between NaBiO3 and CeCl3.7H2O in basic conditions at 200 oC allows the production of nanocrystalline mixed CeIV-BiIII oxides, with crystal size 5-20 nm depending on composition. The average structure of these materials is the fluorite type, as found for δ-Bi2O3, so they may be viewed as solid solutions with oxide ion deficiency to balance charge. The structures of these materials have been studied using neutron diffraction and their redox properties for catalysis have been investigated. Alkali-earth metal peroxides have proved to be useful oxidising agents in hydrothermal synthesis. We can thus prepare a family of pyrochlore oxides, such as Ca2M2O7 (M = Sb, Ru, for example) from M3+ precursors. We will also show in the presence of H2O2 and NaOH a novel Ru(IV) pyrochlore (Na0.33Ce0.67)2Ru2O7 can be produced: this material shows magentic frustration at low temperatures. The pyrochlores formed are metastable and we have used in situ XRD to investigate their collapse. The use of KBH4 in the presence of basic solution has provided us with a useful reducing agent under hydrothermal conditions. We have thus prepared a series of reduced vanadium oxides, including NaV2O5, V2O3, Ba2V3O9 and CaV3O7. These materials, all characterised by X-ray diffraction and electron microscopy, are formed in one step, in contrast to conventional synthetic methods that often require the reduction of a precursor with hydrogen gas at high temperature [1]Demazeau, G., J. Mater. Chem. 1999, 9, 15.[2]Riman, R. E.; Suchanek, W. L.; M.M. Lencka, Annales de Chimie 2002, 27, 15.[3]Modeshia, D.R.; Walton, R. I., Chem. Soc. Rev. 2010, 39, in press. DOI:10.1039/b904702f
12:00 PM - EE1.7
Spontaneous Room Temperature Reactions to Give Complex Metal Oxides and Particle Size Control.
Edmund Cussen 1 , Thomas Yip 1 , Donald MacLaren 2 , Claire Wilson 3
1 Department of Pure and Applied Chemistry, University of Strathclyde, Glasgow United Kingdom, 2 Department of Physics, University of Glasgow, Glasgow United Kingdom, 3 , Rigaku Europe, Sevenoaks, Kent, United Kingdom
Show AbstractThe synthesis of continuous framework solids usually requires high temperatures and long reaction times in order; (i) to break large numbers of bonds in the lattices of the reagents and (ii) to overcome the large activation energies that are typical for ion-diffusion in the solid state. We have recently found a number of direct reactions that proceed at room temperature from stable crystalline starting materials that avoid these requirements. These reactions occur without the use of heating or purification steps and so are extremely efficient routes to new compounds that may be unstable under higher temperature synthetic conditions. Direct reaction between lithium hydroxide monohydrate and molybdenum trioxide leads to the formation of lithium molybdate within minutes at room temperature. This reaction occurs without input of either thermal or mechanical energy and calorimetery measurements show that this spontaneous reaction is endothermic. This suggests that the reaction is driven by the entropy increase associated with the liberation of water from the lattices of the starting materials and this is confirmed by the failure of anhydrous lithium hydroxide to replicate the reaction. The rapidity of the reaction limits particle growth to give a regular aspect ratio of four with particle sizes in the range 0.1 to 4 μm.A similar approach has been used to prepare the compositional series of layered perovskites H1-xLixLaTiO4 for the first time. Reaction between the solid acid HLaTiO4 and lithium hydroxide monohydrate leads to stoichiometric exchange of Li+ for H+ and a product that retains the morphology of the oxide, indicating that the ion-exchange takes place in the solid state. The material remains crystalline and neutron powder diffraction data show that H+ are found in crystallographically-disordered hydroxyl units, whilst the Li+ cations are four coordinated by oxide in a unusual geometry that is intermediate between tetrahedral and square planar. As facile solid-state ion-exchange is required for this reaction it is likely that this reaction will produce new fast-ion conductors.(1) T. W. S. Yip, E. J. Cussen and C. Wilson, Dalton Trans., 2010, 39, 411. (2) T. W. S. Yip, E. J. Cussen and D. A. MacLaren, Chem. Commun., 2010, 46, 698.
12:15 PM - EE1.8
Complex Nanostructures from Layered Metal Chalcogenides.
Wolfgang Tremel 1 , Aswani Yella 1 , Faegheh Hoshyargar 1 , Steffen Pfeiffer 1 , Martin Panthoefer 1 , Enrico Mugnaioli 2 , Ute Kolb 2
1 Institut für Anorganische Chemie und Analytische Chemie, Johannes Gutenberg-Universität, Mainz Germany, 2 Institut für Physikalische Chemie, Johannes Gutenberg Universität, Mainz Germany
Show AbstractIn addition to carbon nanotubes, non-carbon nanostructures have attracted much attention over the past few years. In particular, inorganic nanotubes and fullerenes have become a key topic in nanoscale research. Chalcogenide nanostructures are of interest for a variety of applications ranging from nanotribology, nanoelectronics or battery materials to the active use in heterogeneous catalysis. Similar as their carbon congeners the chalcogenide nanoparticles are not equilibrium but high-temperature and low-pressure phases in the that are obtained by quenching “hot” gas phase species. Various approaches to chalcogenide nanoparticles have been established so far, among them oxide to sulfide conversion, transport reactions, or from the elements using metal droplets. Except for the oxide to sulfide conversion, which has been scrutinized, the growth mechanism of such nanostructures is still subject to discussion. We have used a novel approach to unravel the formation mechanism of MoS2 nanotubes and fullerenes by taking TEM snapshots of reaction intermediates that were obtained by annealing amorphous Mo-S-I nanoparticle precursors captured from an MOCVD reaction. This approach allows a trapping of reaction intermediates by thermal quenching and a control of the reaction process and monitoring the particle growth by the choice of the experimental conditions (precursor etc.). We used amorphous Mo-S-I precursor nanoparticles to exclude solid state diffusion as a rate determining step in the formation of the nanostructures. Thermal decomposition of the precursors leads in the first step to the formation of giant fullerenes with diameters > 150 nm. At higher temperature fullerene particles segregate within these giant fullerenes. In the next reaction step a “shrink-down” process leads to the formation of tubular MoS2 structures containing fullerene-particles in a peapod-type fashion. In the final steps twinned fullerenes and nested fullerene particles are formed. By changing the reaction parameters nanotubes containing fullerenes with diameters of approx. 10 nm can be obtained. Finally, WxNb1-xS2 “coin roll nanowires” were obtained through reductive sulfidization of core-shell Nb2O5-WO3 precursors. The resulting nanowires with dimensions of several micrometers contain stacks of graphene-type WxNb1-xS2 2D-nanosheets with lateral diameters of about 30 nanometers. The resulting nano-aggregates have not only unprecented tribological properties, they exhibited also excellent electrochemical performance for lithium-ion batteries. By delamination of these stacks free and laterally confined graphene-type sheets could be obtained.
12:30 PM - EE1.9
Homochiral Crystals of Lanthanide Antimony Tartrates: Syntheses, Structures and Properties.
Qiang Gao 1 , Xiqu Wang 1 , Allan Jacobson 1
1 Chemistry, University of Houston, Houston, Texas, United States
Show AbstractA series of new lanthanide antimony tartrates have been synthesized in single crystal form by using aqueous solutions of the anionic cluster Sb2L2, L =(R,R)-O2C(HCO)2CO2, at temperatures below 100 °C. All phases obtained are homochiral, i.e., containing solely the enantiomer (R,R)-tart. Three types of crystal structures are observed from single crystal X-ray structure determinations. In the 0D structure [La(H2L)(H2O)4]2[Sb2L2](H2O)7, space group P1, a=8.059(2), b=8.180(2), c=14.813(4) Å, α=98.87(1) °, β=99.26(1) °, γ=90.60(1) °, separated Sb2L2 clusters are located between La(H2L)(H2O)4 infinite rods. The 1D structure [La(NO3)(H2O)5(Sb2L2)](H2O), space group P212121, a=10.313(1), b=11.391(2), c=17.183(2) Å, consists of helical chains formed by interlinking the Sb2L2 clusters with LaO9 polyhedra. In the 2D structure [(La(H2O)5)2(Sb2L2)3](H2O)5, space group P21, a=8.4442(5), b=26.187(2), c=12.1840(8) Å, β=109.61(1)°, the Sb2L2 clusters are each connected to four LaO9 polyhedra to form infinite slabs. The LaO9 polyhedra are each linked to four Sb2L2 clusters. An isostructural series of the 1D type have been obtained for the complete lanthanide series (La –Lu except Pm), while the 0D and 2D structures are limited only to the large lanthanide cations. To our knowledge, the 1D structure is the first homochiral structure that can be formed by the whole lanthanide series. Measurements of second order nonlinear optical properties on selected 1D samples show weak SHG efficiencies comparable to that of quartz. Other optical properties will be reported.
12:45 PM - EE1.10
Building 3D Materials from Adjustable 2D-units; Towards the Design of a Family of Acentric Bi-based Compounds.
Marie Colmont 1 , Olivier Mentre 1 , Diana Endara 1 , Marielle Huve 1 , Sergey V. Krivovichev 2
1 , Unité de Catalyse et de Chimie du Solide, Villeneuve d'Ascq France, 2 , Saint Petersbourg State University, Saint Petersbourg Russian Federation
Show AbstractWe have investigated the possibility to design new inorganic Bi-based phosphates from the intergrowth of versatile building units (Bus). In the large series of compounds predicted/synthesized up today, a structural description based on the arrangement of original Bus has been used to evidence the relationship existing between all members. The Bus consist of 2D ribbon-like polycations formed of edge-sharing oxo- centered O(Bi,M)4 tetrahedra, with versatile size (n tetrahedral-long). The intergrowth between them is performed by PO4 isolated groups, which also create 1D-cationic channels. The stability of such polymorphs is achieved by the possibility of particular sites to guest mixed Bi3+/Mn+ cations, leading to a good chemical adaptability. Here, we show the possibility to stabilize a broad series of those Bus, covering any possible n values, from the chain (one O(Bi,M)4 tetrahedron wide) to the infinite planes. A mega series of new intergrowths has been fully anticipated, prepared and characterized thanks to a design based on empirical rules priory deduced from known parent-members. Finally, it is noteworthy that for particular n values (n = 3n’ + 2), the BUs are polar and arrange in acentric structural types. The deviation from centrosymmetry in term of electronic density repartition is due to Bi3+ position and then rather strong. For example compounds with n= 5, n= 8 and n= 11 have been reached and show second harmonic generation (SHG).
EE2: Solid State Materials - Perovskites
Session Chairs
Kosmas Prassides
Richard Walton
Monday PM, November 29, 2010
Ballroom A, 3rd floor (Hynes)
2:30 PM - **EE2.1
Topochemical Synthetic Routes for the Construction of Metal-nonmetal Arrays within Layered Perovskite Hosts.
Jonglak Choi 1 , K. G. Sanjaya Ranmohotti 1 , Elisha Josepha 1 , Dariush Asadi 1 , Dana Whitemore 1 , John Wiley 1
1 Department of Chemistry and Advanced Materials Research Institute, University of New Orleans, New Orleans, Louisiana, United States
Show AbstractEfforts to develop topochemical reaction strategies are motivated in the short term by the promise of new compounds with interesting structures and in the long term by the desire to develop a library of reactions, akin to that available to the modern organic chemist. Herein we present recent results on new metal-nonmetal arrays constructed within layered perovskite hosts. Sequential intercalation reactions based on reduction and oxidation steps direct the formation of several compounds including a series of halides and chalcogenides. The synthesis and characterization of compounds of the general formula, (A2Xn)LaNb2O7 (A = alkali metal, X = halide or chalcogenide), will be presented along with a discussion on compound stability. Further, the implication of this work for the long term development of topochemical reactions will be highlighted.
3:00 PM - EE2.2
A-Site Magnetism in A-Site-ordered Perovskites.
Takashi Saito 1 , Ryuta Yamada 1 , Hiroshi Shiraki 1 , Yuich Shimakawa 1
1 Institute for Chemical Research, Kyoto University, Uji, Kyoto, Japan
Show AbstractA-site ordered perovskite oxides AA’3B4O12 provide a rich variety of physical properties, such as from metals to insulators and from ferromagnetism to antiferromagnetism. The compounds accommodate transition metals at the 3/4 of the A site (A’ site) of the simple perovskite ABO3, because the BO6 octahedra are heavily tilted in the 2a × 2a × 2a unit cell (a: unit cell of a cubic simple perovskite), to form square planner coordination at the A’ site. The transition metals with partially filled d bands at the A’ site can produce electronic interactions between A’-A’ and/or A’-B sites, in addition to the ordinary B-B interaction, which gives rise to novel functions beyond simple perovskites. In this study, we are very interested in synthesizing new A-site ordered compounds with A-site magnetism. In search for new materials we first examine the structural stability using a computer program SPuDS and choose candidate compositions. We then prepare the samples under high pressure conditions because they often need such extreme conditions to stabilize the highly distorted perovskite structure. We succeeded in obtaining CaCu3Sn4O12 with A’-site Cu2+ (S = 1/2) ferromagnetim [1]. We also synthesized Ln2/3Cu3B4O12 with magnetic lanthanides at the A site. Magnetic interactions between A’-A’ and A’-A were investigated, and the magnetism of these compounds are discussed. [1] H. Shiraki, et al., Phys. Rev. B 76, 140403(R) (2007), Y. Shimakawa, et al., J. Phys. Soc. Jpn. 77, 113702 (2008).
3:15 PM - **EE2.3
Thermal Expansion, Chemical Expansion, Ferroelasticity and Valance State of Mn in Sr Substituted LaMnO3±δ.
Julian Tolchard 1 , Sverre Selbach 1 , Tor Grande 1
1 Materials Science and Engineering, NTNU, Trondheim Norway
Show AbstractSr substituted lanthanum manganites are among the most studied magnetic oxide materials, showing colossal magnetoresistance, and are also the state of the art cathode materials in SOFCs. The magnetic, electrical and thermal properties of these perovskite materials are strongly dependent on both the alkaline earth substitution level and the oxygen stoichiometry. Here we report on a high temperature X-ray diffraction study of Sr substituted LaMnO3±δ. The anisotropic thermal expansion of the materials is reported, and the crystallographic data are discussed in relation to the ferroelastic to paraelastic transition, as previously reported for the isostructural material LaCoO3 [1,2]. Chemical expansion of the manganites was also measured by recording diffraction data at two different oxygen partial pressures. At low substitution level and high partial pressure of oxygen, the materials are oxygen hyper-stoichiometric due to oxidation of Mn3+ to Mn4+. In this region the oxidation state of Mn is affected and controlled by slow diffusion of cation vacancies [3,4]. At high substitution level, the materials become oxygen deficient and the valance state of Mn is equilibrated fast due to the significantly faster diffusion of oxygen vacancies. The importance of the valance state of Mn in perovskites is discussed with examples from multiferroic BiFe1-xMnxO3+δ [5], YMnO3 and HoMnO3. Finally we discuss the important possibility of chemical strain relaxation of thin films in materials containing transition metal cations. 1. J. Mastin, M.-A. Einarsrud and T. Grande, Chem. Mater. 18 (2006) 1680-1687.2. J. Mastin, M.-A. Einarsrud and T. Grande, Chem. Mater. 18 (2006) 6047-6053. 3. L. Rørmark, K. Wiik, S. Stølen and T. Grande, J. Mater. Chem. 12 (2002) 1058-1067.4. M. Palcut, K. Wiik and T. Grande, J. Phys. Chem. B 111 (2007) 2299-2308.5. S.M. Selbach, T. Tybell, M.-A. Einarsrud and T. Grande, Chem. Mater. 21 (2009) 5176-5186.
3:45 PM - EE2: Perovskites
BREAK
4:15 PM - **EE2.4
Physical Properties of Ternary Rare-earth Germanides.
Haiying Bie 1 , Arthur Mar 1
1 Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada
Show AbstractAlthough numerous ternary rare-earth germanides RE–M–Ge have been previously identified (especially with M = Fe, Co, Ni, Cu), much less is known about those containing an early transition metal. Among these, RETiGe3 is an unusual example of an intermetallic phase adopting the hexagonal perovskite structure type (BaNiO3- or BaVS3-type), consisting of isolated chains of face-sharing metal-centred octahedra. CeTiGe3 orders ferromagnetically at TC of 14 K. We have now extended this series to REVGe3 and RECrGe3. The substitution with V leads to the development of antiferromagnetism, whereas the substitution with Cr dramatically increases the critical temperatures for ferromagnetic ordering, coinciding with transitions in the electrical resistivity. Solid solutions involving mixtures of different transition metals (M = V, Cr, Mn) were also investigated.
4:45 PM - EE2.5
New Materials Research: Crystal Growth and Magnetic Properties of the Perovskite Osmium Oxide and Related Compounds.
Kazunari Yamaura 1
1 , National Institute for Materials Science, Tsukuba Japan
Show AbstractOur group is currently conducting a new materials research toward superconducting and magnetic phenomena emerge in transition metal oxides. A hot material currently we study is the complex osmium oxide, such as NaOsO3, Na2OsO4, and Ca3LiOsO6, prepared under a high temperature and high pressure condition [1-3]. They are newly synthesized or remain unstudied so far. The perovskite NaOsO3 shows a metal-insulator transition (MIT) coupled with an antiferromagnetic transition at 410 K [1]. The MIT features are qualitatively comparable with what were observed for Cd2Os2O7 (T_MIT = 226 K), and do not meet the MIT features observed for LnNiO3 (Ln = Pr, Nd, Sm). The MIT likely accords with the Slater transition scheme. Na2OsO4 and Ca3LiOsO6 each have a fully opened electronic gap, being consistent with predictions from the first principles study [2,3]. It appears that Ca3LiOsO6 is highly valuable to study nature of extended superexchange magnetic interaction in solid [3]. In this talk we will overview progress of our research on the osmium oxides. [1] Y. G. Shi et al., Phys. Rev. B 80, 161104(R) (2009).[2] Y. G. Shi et al., J. Solid State Chem. 183, 402(2010).[3] Y. G. Shi et al., J. Am. Chem. Soc. 132, 8474 (2010).
5:00 PM - EE2.6
Phase Transitions in Cu2+ Based Double Perovskites.
Don West 1 , Peter Davies 1
1 Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States
Show AbstractRecent studies have shown that ordered nanoscale microstructures can be achieved in Jahn-Teller distorted spinels through phase separation into cubic and tetragonal phases[1], thus making nanomaterials available using facile solid state synthesis. This work presents the study of a similar family of double perovskite solid solutions featuring Jahn-Teller distorted Cu(II) and mixed valence for both the A-site (2+/3+) and B-site (2+/5+). These materials exhibit a complex array of octahedral tilt systems, with evidence for multiple tilt systems co-existing over temperature ranges larger than 10 °C. Structures are characterized by electron and synchrotron X-ray diffraction. Through chemical substitution, we observe a large temperature range (~700 °C) over which the Jahn-Teller distorted samples transition to cubic symmetry. High temperature diffraction studies on samples made under a variety of annealing conditions reveal interesting aspects of cation ordering at the synthesis temperatures. Also, the introduction of oxygen vacancies disrupts the cation ordering by an unexpected preference to be located between pairs of 5+ B-site cations, rather than between Cu2+/M5+ pairs. While an end member of the solid solution, with no vacancies, transitions to cubic symmetry around 1000 °C, 2% oxygen vacancy results in cubic symmetry at room temperature. Calculations are underway to understand the energetics of oxygen vacancies in these systems. The microstructure of these materials are currently being investigated with transmission electron microscopy. Initial observations show similarity to the spinels mentioned above. Results will be discussed.[1] - Zhang, C.L. et al. Magnetic nanocheckerboards with tunable sizes in the Mn-doped CoFe2O4 spinel. Appl. Phys. Lett. 91, 233110-3 (2007).
5:15 PM - EE2.7
Perovskites with Broken Corner Sharing Connectivity of the Octahedral Framework.
Graham King 1 3 , Artem Abakumov 2 4 , Patrick Woodward 3 , Anna Llobet 1 , Evgeny Antipov 4
1 LANSCE, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 3 Chemistry, The Ohio State University, Columbus, Ohio, United States, 2 EMAT, University of Antwerp, Antwerp Belgium, 4 Chemistry, Moscow State University, Moscow Russian Federation
Show AbstractThe ideal perovskite (ABX3) and double perovskite (A2BB'X6) structures consist of corner sharing networks of BX6 (or BX6 and B'X6) octahedra with the A-site cations filling the voids within the network. Octahedral tilting distortions are commonly observed in perovskites when the A-site cation is too small to fill these voids. The tilting distortions will lower the symmetry below cubic and lead to larger supercells. The possible space group symmetries and lattice vectors that can result from the various combinations of in-phase and out-of-phase octahedral tilting modes have already been enumerated for simple ABX3 perovskites and most cation ordered variants using group theoretical methods. When deriving the possible structures that can result from octahedral tilting it is always assumed that the corner sharing connectivity of the octahedral framework must be maintained. Here we present our work on two double perovskite related compounds, K3AlF6 and Sr3WO6, in which the tilting is not cooperative and the corner sharing connectivity of the octahedral framework is broken. By removing the restriction of corner sharing connectivity it is possible to obtain new structure types that have not been characterized before. Both of these compounds are found to pass through a series of phase transitions upon heating from room temperature, eventually adopting the cubic double perovskite structure at high temperature. The structures of these phases are exceptionally complex and have been solved using a combination of electron diffraction, synchrotron powder X-ray diffraction, and neutron powder diffraction. The structures that exist at temperatures below the transition to cubic symmetry involve ~45° rotations of some of the smaller AlF6 or WO6 octahedra. These large rotations serve to increase the coordination numbers of the larger B-site K or Sr ions from 6 to 7 or 8. In the case of Sr3WO6 a polar crystal structure results. The crystal chemistry required to stabilize such structure types is discussed. It is shown that the primary requirements needed to observe such patterns of octahedral tilting are a very large size mismatch between the B and B' cations and a small tolerance factor. We also show using pair distribution function (PDF) analysis that the local structure of the high temperature phase of K3AlF6 differs greatly from its average cubic structure.
5:30 PM - EE2.8
Magnetic Properties of A-site Mn Ions in A-site-ordered Perovskites AMn3B4O12.
Takenori Tohyama 1 , Takashi Saito 1 , Masaichiro Mizumaki 2 , Yuichi Shimakawa 1
1 Institute for Chemical Research, Kyoto University, Uji Japan, 2 Japan Synchrotron Radiation Research Institute, SPring-8, Hyogo Japan
Show AbstractA-site-ordered perovskites AA’ 3B4O12, in which A and A’ ions are ordered at A site in a simple perovskite structure, have considerable attraction recently because they show useful and intriguing physical properties. For example, CaCu3Ti4O12 shows large dielectric response at room temperature and LaCu3Fe4O12 shows unusual intersite charge transfer between A-site Cu ion and B-site Fe ion. The A’ site in this structure is usually occupied by Jahn-Teller ions such as Cu2+ or Mn3+. In order to stabilize these transition metal ions at the originally 12-fold coordinated site in a simple perovskite structure, the BO6 octahedra are heavily tilted, resulting in A’O4 square planar oxygen coordination. In this study, we focus on the magnetic interaction between the A’ site Mn ions. With high-pressure synthesis technique, we succeeded in synthesizing several new AMn3B4O12 materials. For YMn3Al4O12, the structural analysis with synchrotron x-ray diffraction data and the Mn L-edges x-ray absorption spectrum revealed that the compound had a chemical composition Y3+Mn3+3Al3+4O2-12 with magnetic Mn3+ at the A’ site and non-magnetic Al3+ at the B site[1]. From the magnetization measurements, antiferromagnetic interaction between the Mn3+ spins was confirmed[1]. The result of electronic structure calculation suggested that the antiferromagnetic property was mainly caused by Mn-Mn direct magnetic exchange interaction[1]. We will also present experimental results of structural and magnetotransport properties of AMn3Ti4O12 and discuss the differences from those of AMn3Al4O12. [1] T.Tohyama, et al. Inorganic Chemistry 49, 2492 (2010).
5:45 PM - EE2.9
Direct Mapping of Structural Distortions in Perovskites Using Aberration-corrected STEM.
Albina Borisevich 1 , Hye Jung Chang 1 , Oleg Ovchinnikov 2 , Mark Oxley 1 , Ramamoorthy Ramesh 3 , Stephen Pennycook 1 , Sergei Kalinin 1
1 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 , University of Tennessee, Knoxville, Tennessee, United States, 3 , University of California Berkeley, Berkeley, California, United States
Show AbstractStructural distortions of MO6 octahedra such as Jahn-Teller splitting and cation off-centering, and distortions of octahedral network such as tilts, underpin the functionality of a large number of perovskite-based materials. At interfaces, discontinuities in these parameters give rise to new functionalities that do not exist in the bulk, including interface superconductivity, improper ferroelectricity, and magnetoelectric coupling phenomena. Furthermore, at ferroelastic domain walls, symmetry changes alone often give rise to new properties. With the advent of the aberration correction, it became possible to map structural distortions on a unit cell scale, from polarization to octahedral tilts. Here we report on the application of the STEM structural analysis to reveal structural origins of new interface properties in multiferroic thin films.Epitaxial BiFeO3 (BFO) film was grown using molecular-beam epitaxy on single-crystal SrTiO3 (STO) substrates. A thin layer of epitaxial (La,Sr)MnO3 (LSMO) was used as a bottom electrode to facilitate electrical contact and heteroepitaxial growth. STEM images and EEL spectra were collected using a VG Microscopes HB 603 U operated at 300 kV, equipped with a Nion aberration corrector and Gatan Enfina® spectrometer.The direct quantitative unit-cell-by-unit-cell mapping of oxygen octahedral tilts across the interface is performed using bright field STEM images, elucidating how the change of crystal symmetry is accommodated. Combined with low-loss electron energy loss spectroscopy imaging, we demonstrate a mesoscopic antiferrodistortive-induced phase transition in a thin layer directly adjacent to the interface [1]. Beyond direct imaging, we introduce a method for order parameter mapping in complex oxides based on a shape analysis of Z-contrast images of the heavy atomic columns. In a thick sample the light atomic columns such as O columns are not resolved. However, the overlap of the Bi and O columns distorts the shape of the Bi column. Using principal component analysis (PCA) the column shape can be identified based on eigenshapes, and corresponding loading maps provide the spatial distribution of the symmetry-resolved distortions.This research was sponsored by the Division of Materials Science and Engineering, office of Basic Energy Sciences, US DOE (AB, HJC, SJP and SVK). OO was supported by the ORNL HERE program.References[1]A. Borisevich et al., arXiv:1002.2989v1 [cond-mat.mtrl-sci].
EE3: Poster Session: Solid State Chemistry of Inorganic Materials VIII
Session Chairs
Tuesday AM, November 30, 2010
Exhibition Hall D (Hynes)
9:00 PM - EE3.1
Luminescent Enhancement of SrSi2O2N2:Eu2+ Through Doping with Mg and Y.
Kang Sik Choi 1 , Chang Hae Kim 1
1 , Korea Research Institute of Chemical Technology, DaeJeon Korea (the Republic of)
Show Abstract SrSi2O2N2:Eu2+ phosphors were prepared by conventional solid state method in reduction atmosphere. The phosphor has 534 nm main emission peak under 450 nm excitation light. Mg2+ and Y3+ were added in raw materials to improve the emission efficiency. The emission efficiency of metal-codoped phosphor was higher than that of non-codoped phosphors, about 40%. There was no change of crystal structure when Mg2+ and Y3+ cations were added. This green phosphor and a red phosphor could make white light with InGaN blue LED.
9:00 PM - EE3.12
Process Development for Synthesis of Oxynitride Phosphors.
Shyan-Lung Chung 1 , Yen-Chun Liu 1 , Huang Shu Chi 1
1 , NCKU, Tainan Taiwan
Show AbstractOxynitride phosphors have been reported to be of potential for applications in solid state lighting.However, presently available methods for the synthesis of oxynitride phosphors all require relatively severe conditions such as high temperature, high pressure and long reaction duration. In this presentation, we report the development of a new method for the synthesis of a yellow oxynitride phosphor (i.e.,Ca-α-SiAlON:Eu2+) based on self-propagating high temperature synthesis (SHS) reactions. The reactants used for the synthesis include calcium, silicon, aluminum, silicon nitride and europium oxide. These powders are mixed and pressed into compacts. The reactant compacts are then wrapped up with an igniting agent (e.g., Al+Fe3O4) . The reactant compact is ignited by electrical heating under a N2 atmosphere of 5 atm. The Ca-á-SiAlON:Eu2+ phosphor can thus be produced under a low pressure and a short duration time. We also investigated the effects on the properties of the product of several important experimental parameters including compositions and different ratios in the amount of reactant compact and igniting agent. The luminescence properties are also compared with the commercial phosphors. The results showed that the luminescence intensity and wavelength of the Ca-α-SiAlON:Eu2+ phosphors are affected by experimental parameters. A typical product has an excitation spectrum in the range of 220-500nm and a single broadband emission in the range of 400-670nm centered at 555nm upon excitation at 380nm. The luminescence intensity is 94.1% as compared with a corresponding commercial phosphor.
9:00 PM - EE3.13
Synthesis of New Layered Oxides through a Multistep Approach.
Elisha Josepha 1 , Catherine Rodriguez 1 , Lea Gustin 1 , John Wiley 1
1 Department of Chemistry and Advanced Materials Research Institute, University of New Orleans, New Orleans, Louisiana, United States
Show AbstractTopotactic methods allow for the formation of new compounds while maintaining salient structural features. By combining such methods, one can design a multistep approach that leads to the formation of products not obtainable through traditional solid state techniques. The synthesis of a series of new compounds, (AxCly)M0.5LaM’2O7 (A = Li, Rb; M = Fe, Ni, VO; M’ = Nb,Ta), was investigated. Initially, M0.5LaM’2O7 (M = Fe, Ni) and (VO)0.5LaNb2O7 were made through ion-exchange. This was followed by a reductive intercalation step with n-butyllithium or Rb metal to produce, AxM0.5LaM’2O7 (x ≤ 1.5). Subsequently, an oxidative intercalation step was carried out using chlorine gas at room temperature under dynamic flow. Results are consistent with the formation of compounds isostructural with (Rb2Cl)LaNb2O7. Details on the synthesis and the characterization of these new layered compounds will be presented and discussed.
9:00 PM - EE3.14
One–Dimensional Growth of Ruthenium Oxide.
Lamartine Meda 1 , Geoffrey Stevens 1
1 Chemistry, Xavier University of LA, New Orleans, Louisiana, United States
Show AbstractRuthenium oxide (RuO2) nanometer-sized rods have been grown by metalorganic chemical vapor deposition (MOCVD) on glass substrates at 400 C by controlling the oxygen content in the gas mixture, the distance of the substrate to the precursor, and the rate of evaporation of the precursor. The precursor used in the deposition process was ruthenocene and the nanorods were grown without employing any metal catalysts, which is usually needed for one dimensional (1-D) growth structure by CVD. Field-emission scanning electron microscopy (FE-SEM) equipped with EDAX show the rods ranging from 50 to 90 nm in diameter and X-ray diffraction revealed that the rods are polycrystalline. A growth mechanism for the RuO2 nanorods is proposed.
9:00 PM - EE3.15
Synthesis of Hierarchical Layered Titanate Microspherulite for Efficient Pollutant Treatment in Aqueous Media.
Yuxin Tang 1 , Dangguo Gong 1 , Yuekun Lai 1 2 , Zhili Dong 1 , Zhong Chen 1
1 School of Materials Science and Engineering, Nanyang Technological University, Singapore Singapore, 2 State Key Laboratory of Physical Chemistry of Solid Surfaces and College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, Fujian, China
Show AbstractAn ultrafast and template-free method to synthesize three-dimensional (3D) hierarchical layered titanate microspherulite (TMS) particles with high surface area is reported. The synthesis makes use of an electrochemical spark discharge spallation (ESDS) process, during which fast anodic reaction on titanium surface creates a layer of titanium dioxide that instantly breaks down by the applied electrical field into the solution in the form of titanium oxide particles. The spalled particles readily react with the heated NaOH electrolyte to form the titanate particles. A typical as-prepared TMS with a diameter of 0.4~1.5 µm and high surface area of ~406 m2g-1 is synthesized by ESDS of Ti foils in 10 M NaOH solution under an applied current density of 0.5 Acm-2, leading to a reaction yield of approximately 0.10~0.15 g per square centimetres of exposed Ti foil within 20 min. On the Ti surface, crystalline rutile TiO2 nanoporous structure is formed, which is attributed to the local exothermic heat caused by the spark discharge. The formation mechanism of the TMS is discussed based on field emission scanning electron microscopy (FESEM) study and Raman scattering spectroscopy analysis. The as-prepared TMS shows excellent adsorption performance compared with a titanate micro-particle (TMP), nanowire (TNW) and nanotube (TNT) when methylene blue (MB) and PbII ions are used as representative organic and inorganic pollutants. The mechanism of adsorption has also been discussed.[1] Y. X. Tang, Y. K. Lai, D. G. Gong, K.-H. Goh, T.-T. Lim, Z. L. Dong, Z. Chen. Chem. Eur. J., 2010, doi: 10.1002/chem.201000330.[2] Y. X. Tang, D. G. Gong, Y. K. Lai, Y. Q. Shen, Y. Y. Zhang, Y. Z. Huang, J. Tao, C. J. Lin, Z. L. Dong, Z. Chen. 2010, submitted.[3] Y. K. Lai, Y. C. Chen, Y. X. Tang, D. G. Gong, Z. Chen, C. J. Lin. electrochem.Commun., 2009, 11, 2268-2271.
9:00 PM - EE3.16
Thermodynamic Aspects of Transition Metals Doped ZnO.
David Sedmidubsky 1 , Zdenek Sofer 1 , Jindrich Leitner 1
1 , Institute of Chemical Technology, Prague Czechia
Show AbstractDilute magnetic semiconductors (DMS) recently attracted great attention as potential candidates for spintronic applications. Among them, wide band gap DMS such as GaN and ZnO doped by transition (TM) and rare-earths metals reveal relatively high transition temperatures into ordered ferromagnetic state which makes them attractive for room temperature applications. However, there is nowadays a strong evidence of inhomogeneous character of the ferromagnetic state in wide band gap DMS, frequently coexisting with a prevailing paramagnetic phase. These observations suggest a possible tendency to clustering of magnetic impurities which might be a precursor for real phase separation. In TM doped ZnO, the competing phase whose thermodynamic stability limits the solubility of TM in ZnO wurtzite structure is the ZnTM2O4 spinel. The ferromagnetic behavior can thus be attributed either to nano-scale regions in ZnO enriched by TM or to spinel clusters whose magnetic behavior can differ from bulk material (usually ordered antiferromagnetically).In this paper we present a thermodynamic study of Cr, Mn, Fe solubility in ZnO based on the assessment of available thermodynamic data, our DSC experimental results and ab-initio calculations in the respective TM-Zn-O systems. The ab-initio DFT calculations of enthalpies of formation of the involved phases and the energies of substitutional defect (TM-Zn) formation were performed using the full-potential APW+lo technique (WIEN2k code) within GGA+U approximation. The entropies at the reference temperature 298 K of some selected phases were evaluated from low temperature heat capacity either measured by relaxation method or calculated by direct method within harmonic crystal approximation (Phonon program). The calculated energies of mixed oxides and virtual (unstable) TMO end-members of (Zn,TM)O solid solutions were referred to well established thermodynamic data of binary oxides taken from SGTE database. The assessed thermodynamic data were subsequently used for calculation of phase equilibria and construction of the respective phase diagrams. Since the TM exhibit a variable TM valency in different involved phases, the phase equilibria including the TM solubility in ZnO are dependent on oxygen potential, p(O2). Hence the presented results are actually the sections of p(O2)-T-x phase diagram, where x refers to Zn/TM ratio. The preliminary results suggest the TM solubility in ZnO not exceeding 1 mol% which is below the nominal TM concentrations in commonly prepared ZNO based DMS. The analysis of magnetic properties of ZnO ceramics and thin films with low doping rates of Cr, Mn, and Fe will be also presented.
9:00 PM - EE3.17
Stable Complex Oxides of Pd2+ and Au3+ as Model Compounds for Heterogeneous Catalysis.
Joshua Kurzman 1 , Xiaoying Ouyang 1 , Susannah Scott 1 4 , Ram Seshadri 1 2 3
1 Chemistry and Biochemsitry, University of California Santa Barbara, Santa Barbara, California, United States, 4 Chemical Engineering, University of California Santa Barbara, Santa Barbara, California, United States, 2 Materials, University of California Santa Barbara, Santa Barbara, California, United States, 3 Materials Research Laboratory, University of California Santa Barbara, Santa Barbara, California, United States
Show AbstractAn emerging paradigm in catalysis is the use of PGM ions, as opposed to PGM nanoparticles, as oxidation catalysts. One particular class of PGM-substituted complex oxides, dubbed "intelligent catalysts," undergo reversible redox cycles, extruding PGM metal ions out of the oxide host as nanoparticle precipitates under reducing conditions, and reincorporating the precious metal into the framework under oxidizing conditions. Such materials suppress the sintering of nanoparticles under working conditions through this egress/ingress behavior, which occurs in response to the characteristic redox fluctuations in an exhaust stream. Previous work in our group identified the perovskite BaCeO3, and the metastable hexagonal compound YFeO3, as suitable host lattices for Pd2+. In both cases, the most active catalysts were found to be the fully oxidized materials containing Pd ions in the host. In this context, we explore some aspects of the solid state chemistry and reactivity of well defined compounds containing isoelectronic Pd2+ and Au3+, as model compounds for probing heterogeneous catalysis by noble metal ions. Though La2BaPdO5 and La4LiAuO8 are both square planar d8 compounds, they show widely different activity for CO oxidation. We address this difference in the context of the density functional electronic structures of these model systems.
9:00 PM - EE3.18
Rhombohedral-tetragonal Transition and Enhancement of Piezoelectric Constant in (1-x)BiFeO3-xBiCoO3 Solid Solution Thin Films.
Yoshitaka Nakamura 1 , Masanori Kawai 1 , Masaki Azuma 1 , Yuichi Shimakawa 1
1 Institute for Chemical Research, Kyoto University, Uji, Kyoto Japan
Show AbstractPb(Zr,Ti)O3 (PZT), a solid solution between PbZrO3 and PbTiO3, shows an excellent piezoelectric property at a morphotropic phase boundary (MPB) between rhombohedral and tetragonal phases. There is growing interest in development of lead-free replacement because the toxic lead causes environmental problems. We are studying similar rhombohedral-tetragonal solid solution (1-x)BiFe3-xBiCoO3 (BFCO) as a candidate lead free piezoelectric material. Bulk BFCO changes from BiFeO3-type rhombohedral structure to BiCoO3-type tetragonal one with a large tetragonality (c/a = 1.26) at around x = 0.25 and these two phases coexist at the phase boundary [1]. Epitaxial BFCO thin films (x = 0 - 0.30) were prepared on SrTiO3 (STO) and LaAlO3 (LAO) (001) substrates by chemical solution deposition. The structural changes of the films were investigated by measuring reciprocal space mappings of X-ray diffraction. The films on STO (cubic with a lattice parameter a = 3.90 Å) showed gradual second order change from rhombohedral to tetragonal phases at around x = 0.15 - 0.20. The rhombohedral phase was relaxed from the substrates while the tetragonal phase was fixed to the substrates. The c/a of the tetragonal phase (x = 0.30) is 1.03, far smaller than the bulk value of 1.26 [2]. This small c/a should be attributed to the tensile strain from STO substrate which elongated the in-plane lattice constant of the BFCO film. On the other hand, films on a substrate with a small lattice parameter, LAO (rhombohedral with a pseudocubic lattice parameter a = 3.79 Å), showed a distinct structural change. Relaxed rhombohedral phase with a = 3.95 Å, α = 89.7o was observed for x = 0 - 0.05 while strained tetragonal phase with a = 3.79 Å and c = 4.65 Å (c/a = 1.23) was observed for x = 0.20 - 0.30. Both rhombohedral and tetragonal phases coexists for x = 0.075 - 0.15. The piezoelectric properties of the films were evaluated with an atomic force microscope system. The piezoelectric constant, d33, estimated from a slope of a displacement-electric field curve for BiFeO3 film on LAO was 51 pm/V. The d33 value increased with increasing the Co content and reached maximum value of 100 pm/V at x = 0.10, rhombohedral-tetragonal MPB composition. The d33 value then decreased as the fraction of the tetragonal phase further increased. It is therefore confirmed that Co substitution for Fe in BiFeO3 leads to a formation of a rhombohedral-tetragonal MPB and the enhancement of piezoelectric constant. [1] M. Azuma, S. Niitaka, N. Hayashi, K. Oka, M. Takano, H. Funakubo, and Y. Shimakawa, Jpn. J. Appl. Phys. 47, 7579 (2008). [2] Y. Nakamura, M. Kawai, M. Azuma, and Y. Shimakawa, Jpn. J. Appl. Phys. 49, 051501 (2010).
9:00 PM - EE3.19
Structure Analysis and Photocatalytic Properties of Novel Spinel Zinc Gallium Oxy-nitride Photocatalysts.
Bharat Boppana 1 , Raul Lobo 1
1 Department of Chemical Engineering, University of Delaware, Newark, Delaware, United States
Show AbstractNovel zinc gallium oxy-nitrides, with the spinel structure and visible light band gaps, have been synthesized by nitridation of zinc gallate, produced by sol-gel synthesis. These spinel oxy-nitrides have band gaps of 2.5 to 2.7 eV, surface areas of 16 to 36 m2/g, and nitrogen content less than 1.5%. They also degrade methylene blue dye in visible light and produce oxygen from silver nitrate. The reduction in band gap for these oxy-nitrides is associated with the incorporation of nitrogen in the zinc gallate structure and corresponding changes in the anion position parameter as well as the presence of a small fraction of gallium tetrahedral centers and anion vacancies. While spinel oxy-nitrides are produced under nitridation at 550oC, at higher temperatures they are consumed to form wurzitic oxy-nitrides. The wurzite materials also have band gaps less than 3 eV but their surface areas are 2 to 5 m2/g. The changes associated with the gallium coordination (from octahedral to tetrahedral) as the spinel zinc gallate precursor transforms into the spinel oxy-nitride at 550oC, and further changes into the wurzite oxy-nitride at 850oC are studied through x-ray diffraction, ultraviolet-visible diffuse reflectance spectroscopy, neutron powder diffraction, x-ray absorption spectroscopy and other techniques. Electronic structure and formation energies of the spinel and wurzite oxy-nitrides are also studied using density-functional theory (DFT) with the Linear Augmented Plane Wave (LAPW) method at varying dopant concentrations. The protocol developed opens an avenue for the synthesis of semiconductors having the spinel crystal structure and band gaps engineered to the visible region with potential applications for both opto-electronic devices and photocatalytic processes.
9:00 PM - EE3.2
Preparation of Ca7(SiO4)2(PO4)2:Eu Green Phosphors and Their Optical Properties under Near-UV Irradiation.
Ha-Kyun Jung 1 , Sungho Choi 1 , Se-Won Tae 1
1 Advanced Materials Division, Korea Research Institute of Chemical Technology, Daejeon Korea (the Republic of)
Show AbstractIn order to obtain white light emitting diodes (LEDs) with an appropriate color temperature and a high color-rendering index (CRI), in recent, a new approach using near ultraviolet LED chips (near UV LEDs) combined with tricolor phosphors has been introduced. Tricolor phosphor based white LEDs have significant CRI, low color temperature and broad color range that originated from blended phosphor. The performance of white LEDs such as CRI, color temperature and color range can be significantly dependant on phosphors. Therefore, the phosphor materials play an important role in tricolor based white LEDs. Eu2+ activators exhibit wide-ranging emission between around 350 nm and 600 nm, depending upon the crystal field and nephelauxetic effect originated from host material. Also, it is known that phosphors based on phosphates have distinctive characteristics such as good thermal stability and stabilization of ionic charge in the lattice. In this work, Eu2+-activated calcium silicophosphate phosphors for application as a novel green component for white emission using UV LEDs were fabricated. The emission properties under near UV irradiation were optimized with Eu2+ concentration changes. Powder samples of Ca7(1-x)(SiO4)2(PO4)2:Eux2+ were synthesized by a solid-state reaction. After the mixing of raw materials, the mixture were fired at 1200C for 5 h under a reducing atmosphere of 5% H2/N2 gas stream. The crystal structures of the phosphors were investigated by powder X-ray diffraction. To characterize the luminescence properties, the photoluminescence excitation and emission spectra were measured. The X-ray diffraction results indicated that the prepared phosphors are formed to a nagelschmidtite phase with heat treatment at 1200C. In the excitation spectrum, it was observed that Ca7(SiO4)2(PO4)2:Eu phosphor absorbs the ultraviolet ray between 225 nm and 475 nm with the maximum intensity at 370 nm. Under the excitation of 370 nm-wavelength, the Ca7(SiO4)2(PO4)2:Eu phosphor showed broad green emission band centered at 505 nm. Optimum concentration of Eu2+ which exhibits maximum emission intensity was investigated to be 1.5 mole%. As a result, the optimized phosphor can be used as a potential green phosphor for generation of white emission using near UV LEDs.
9:00 PM - EE3.20
Design and Fabrication of Reflective Coatings using the Optical Properties of Oxides.
Evelyn DeLiso 1 , Mei Wen 2 , Jennifer Kruschwitz 3
1 , Stanton Advanced Ceramics, Inc., Cleveland, Ohio, United States, 2 , Consultant, Longmeadow, Massachusetts, United States, 3 , JK Consulting, Inc., Rochester, New York, United States
Show AbstractThe design and fabrication of a reflective thin film coating using atomic layer deposition for a three-dimensional object is described. The coating development is motivated by a desire to replace decorative chrome coatings and to thus create a reflective environmentally friendly coating. A multi-layer oxide thin film is designed and deposited onto a metal substrate. The thin film dielectric stack reflects visible light. A transmission electron micrograph of the deposited layers demonstrates the ability of atomic layer deposition to uniformly deposit the nanostructured layers with remarkable accuracy, thus creating the desired visual effect.
9:00 PM - EE3.21
The True Nature of Conducting Proton in Perovskite Ceramic Membrane.
Aneta Slodczyk 1 , Philippe Colomban 1 , Oumaya Zaafrani 1 , Olivier Lacroix 2 , Beatrice Sala 2
1 , LADIR UMR 7075 CNRS-UPMC, Thiais France, 2 , AREVA NP - CNRS - UM2, Montpellier France
Show AbstractThe proton conducting perovskites are widely investigated due to their high potential as electrolyte membranes in fuel cells, water steam electrolysers and CO2/syngas converters [1]. Prior to this industrial application it is necessary to understand their complex physical/chemical behaviour and clarify numerous discrepancies, especially those ones concerning the amount, type and nature of protonic species at the ceramic surface and in the bulk. Our comprehensive spectroscopic (Raman, IR, neutron), thermogravimetric, elastic and quasi-elastic neutron diffusion as well as conductivity studies performed on Ln/RE- modified zirconates ceramics with controlled densification (90-99% of theoretical density) [2,3] reveal the important differences between the surface and bulk protonic species. The results clearly show that trivialization of the protonation process complexity can favourite the adsorption of the surface protonic species (hydroxide, hydrocarbonates, etc) and prohibit the incorporation of bulk protons, i.e. species responsible for the proton conduction. We will prove that most of available literature data consider the behaviour of surface protonic species only and in consequence the statements concerning the proton nature (ion OH-) and conductivity mechanism should be revised. 1. Ph. Colomban Ed. Proton Conductors, Cambridge University Press, Cambridge (1992) 2. PCT patent WO 2008/152317 A2 (18-12-2008)3. Ph. Colomban et al. J. Phys. Soc. Jpn. 79 Suppl. A (2010) 1-6.
9:00 PM - EE3.23
Thermodynamics of Oxygen Chemistry on PbTiO3 and LaMnO3 (001) Surfaces.
Ghanshyam Pilania 1 , R. Ramprasad 1
1 IMS, CMBE, University of Connecticut, Willimantic, Connecticut, United States
Show AbstractSince the 1970s, perovskite based catalysts have been extensively investigated within the context of a number of reactions. Very recently perovskites, especially when doped, have been shown to be superior (relative to conventional Pt based catalysts) for the treatment of NOx in diesel exhaust. Experimentally, it is difficult to determine the state of the catalytic surface and the nature of the catalytically active local sites during various stages of the catalytic oxidation processes. As a first step towards gaining a microscopic understanding of perovskite-based catalytic process, we present a density functional theory (DFT) study of O ad-atoms and vacancy formation on (001) surfaces of the PbTiO3 (PTO) and LaMnO3 (LMO) cubic perovskites. We first predict the relaxed atomic structure and energetics of clean and O ad-atoms/vacancy covered surfaces. In the case of the PTO (001) surfaces, the adsorbate oxygen atom was found to form a peroxide-type molecular species along with a surface lattice oxygen atom on both PbO- and TiO2-terminated surface facets. On the other hand, the most stable oxygen adsorption site for the LMO (001) surfaces corresponds to the one expected from a natural continuation of the perovskite lattice. Moreover, the dissociative adsorption of molecular oxygen varies from being only slightly exothermic on the PTO (001) facets to being highly exothermic on the LMO (001) facets. Our calculations predict a highly endothermic O vacancy formation process (at zero temperature) for the four surfaces. Through calculation of the Gibbs free energy (by combining 0 K DFT results with statistical thermodynamics) and taking into account the temperature and pressure via the oxygen chemical potential, we further obtain the(p,T) phase diagram of the perovskite (001) surfaces in thermodynamic equilibrium with the gaseous O2. Our results show that, owing to the highly energetically unfavorable nature of O vacancy formation on these surfaces, the surface structures with O vacancies appear only at high temperatures and practically irrelevant low pressures on the (p,T) surface phase diagram. In contrast, effortless formation of thermodynamically favorable O ad-atoms on the surfaces appears as the stable O ad-atom covered surface structures on the surface phase diagrams at practically achievable pressures and temperatures. Above room temperature and close to atmospheric pressures, we predict clean PbO and TiO2-terminated (001) PTO surfaces as the stable surface phases while partially or fully O ad-atom covered surfaces are found to be more stable for the LMO. Our results suggest that besides the variable oxidation states of transition metal ions (e.g., in LMO), the availability of the adsorbed surface O atoms is predicted to play a crucial role in the observed catalytic activity of the perovskite surfaces.
9:00 PM - EE3.24
Ordering Effects on the Crystal Microstructure and Electronic Properties of Gd0.5Ba0.5B1-xB’xO3-δ (B, B’= Mn, Co, Fe).
Susana Garcia-Martin 1 , Subakti Subakti 1 , Daniel Munoz 1 , Miguel Alario-Franco 1
1 , Complutense University, Madrid Spain
Show AbstractTransition metal oxides of general formula Ln1-xAxBO3-δ (Ln=lanthanide A=Ca, Sr, Ba; B=transition metal) with perovskite-related structures do have important electric and magnetic properties. The composition of the compounds, the size of the cations and the ordering or disordering between them play an important role in the modification of such properties. In this sense, charge ordering (CO) and colossal magneto resistance (CMR) have been observed in the Ln1-xAxMnO3 (Ln=Pr, Sm; A=Ca, Sr) systems (1). Variations of the magnetic properties and CO with the substitution of Mn by other transition metal atoms has been reported in the case of Pr0.5Ca0.5Mn1-xBxO3 (B= Fe, Ti, Al, Cr, Ru, Co) (2). In addition to this, some perovskite oxides with Ba and rare earth atoms within the A positions, as for instance Ba0.5Gd0.5MnO3-δ and Ba0.5Gd0.5CoO3-δ, can present layered-type ordering of these cations. This ordering seems to favour the oxygen anion diffusion throughout the structure (3). This fact have developed an increasing interest on materials based on layered perovskites as cathodes for intermediate temperature-operating solid oxide fuel cells.We are studying the influence of the cation ordering and the microstructure in the electronic properties of Gd0.5Ba0.5B1-xB’xO3-δ (B, B’= Mn, Co, Fe). Preparation of these materials under different conditions have a significant effect on the ordering of both the La/Ba cations and the anion vacancies. We present in here a study of these materials by Selected Area Electron Diffraction and High Resolution Transmission Electron Microscopy. We observe different superstructures of the perovskite-type associated to ordering of cations and/or vacancies and to CO effects. We also present the electric and magnetic properties of these materials and the influence of the ordering effects on these properties. References:1.C. Martin, A. Maignan, M. Hervieu and B. Raveau, Phys. Rev. B. 2000, 60, 12191.F.2.Martin, A. Maignan, M. Hervieu and B. Raveau, J. Mag. Magn. Mater.1998, 183, 143; B. Raveau, A. Maignan, and C. Martin, J. Solid State Chem. 1997, 130, 162.3.Taskin A. A., Lavrov A. N., Yoichi A., Progress in Solid State Chemistry 35, (2007), 481.
9:00 PM - EE3.26
Syntheses and Characterization of CdSiO3 in Low Temperatures by Molten Salt.
Leonardo Santana 1 , Flavio Vichi 1 , Erick Sousa 1
1 Department of Chemistry, Usp, São Paulo, São Paulo, Brazil
Show AbstractIon-exchange reactions are used in the synthesis of many important materials. While these reactions are very well known in the gaseous and liquid states, they have received relatively little attention in the solid state. Recently, low temperature reactions have been studied as an alternative to conventional, energy-intensive processes. In this context, soft chemistry routes based on hydrothermal and microwave radiation have been proposed.An interesting alternative, which has not been as extensively explored as others, is the molten-salt synthesis, in which a molten salt flux acts either as a solvent or as a reactant. Cadmium metasilicate (CdSiO3) is an important matrix for use in devices having persistent luminescence, due to its good chemical and physical stability, ease of preparation, and low cost. Therefore, interest in this type of material has been increasing recently.1 Traditionally, cadmium metasilicate has been prepared by solid state synthesis, yielding pure, crystalline CdSiO3 at temperatures ranging from 900 – 1050°C. However, these preparations involve long periods of ball-milling followed by long heating times, typically from 5 to 12 h. Moreover, materials prepared this way exhibit large highly aggregated particles.1Sol-gel routes, which involve the use of tetraethylorthosilicate (TEOS) as the silicon precursor, have also been proposed, but pure CdSiO3 is obtained in pure form only after heat treatments above 870°C for several hours, also yielding large aggregated particles.In this contribution we report the successful preparation of single-phase CdSiO3 nanowires and nanorods at temperatures as low as 360°C. Cadmium chloride and cadmium nitrate were used as a molten reactants. The resulting materials were characterized by x-ray diffraction (XRD), focused ion beam (FIB) microscopy, field-emission scanning electron microscopy (FESEM), surface area by nitrogen adsorption (BET). The characterization confirms the preparation of pure, single-phase, crystalline CdSiO3 nanoparticles in the form of nanowires and nanorods.1Qu, X.; Liu, W.; Su,G.;Qu, H.; Xu, C. J. Alloys Comp. 2009, 484, 641,644
9:00 PM - EE3.28
Effect of Boron on Processing and Phosphorescence Behavior of SrAl4O7 (SA2) Co-doped with Eu2+ and Dy3+.
Murat Gokhan Eskin 1 , Hasan Kurt 1 , Mehmet Ali Gulgun 1 , Cleva Ow-Yang 1
1 Materials Science & Engineering, Sabanci University, Istanbul Turkey
Show AbstractStrontium aluminate phosphors luminesce with sufficiently high intensity to make them attractive for inexpensive lighting and safety illumination applications. It has been noted that the afterglow persistance of such phosphors can be enhanced by addition of boron, although the actual role of boron is not well-understood. To this end, we have investigated the effect of boron on the phosphorescence properties of Eu2+ and Dy3+ co-doped SrO-(Al2O3)2, (SA2). Since B was observed to impact the powder processing as well as the phosphorescence, we intend to present the effect of B incorporation on the processing and optical properties.The use of solution polymerization for the powder processing enabled a surprising degree of control over the crystal structure. Up to 30 mol% B could be introduced into the SA2 crystal lattice without significant perturbation to the monophase structure, as revealed by XRD. We have also observed that addition of B even facilitated maintaining the phase purity of the single-phase SA2. In order to elucidate the role of B on enhancing the phosphorescence properties of Eu2+ and Dy3+ co-doped SA2, the electronic structure was characterized by luminescence spectroscopy and electron energy loss spectroscopy for compounds containing 0, 10, 20 and 30 mol% B. Thermally stimulated luminescence measurements were performed to understand the impact of B on energy trap states, to complement the information obtained from fluroescence and photoluminescence spectra and phosphorescence decay curves Finally, to tie the electronic structure information to the atomic bonding environment, electron energy loss spectroscopy in the TEM was performed. Inspection of the ELNES revealed that B occupies neither pure BO3 or pure BO4 coordination polyhedra in the SA2 compound.
9:00 PM - EE3.29
Single Step Synthesis of Pb(Mg1/3Nb2/3)O3 from an Aqueous Suspension.
Marija Kosec 1 , Gregor Trefalt 1 , Barbara Malic 1 , Danjela Kuscer 1 , Janez Holc 1
1 , Jozef Stefan Institute, Ljubljana Slovenia
Show AbstractThere are firm principles concerning solid state synthesis of oxide powder i.e. particles of starting compounds should be small and as much as possible homogeneously distributed to each other. It is very true for simple binary system, however not necessary true for complex system involving several starting compounds that may show also complex reaction pathway during heating. It is quite common that non desirable reaction and non desirable compounds that form at lower temperatures finally react to final product, however its phase purity and chemical homogeneity is questionable. In many cases simple solid state synthesis is therefore not useful. The question is how to avoid parasitic reactions and how to force the correct one. We demonstrated that by manipulation of pH and consequently the surface charge of starting compound in water suspension we limited the contacts between those starting compounds that give non desirable product and brought to the contact those species that were needed for final product. Pb(Mg1/3Nb2/3)O3 (PMN) is a relaxor with high dielectric and electrostrictive properties. One of the major problems related to PMN is the difficulty to prepare pure perovskite phase via a conventional solid state synthesis from constituent compounds. Due to the high reactivity of lead and niobium reactant compounds, secondary pyrochlore PbyNbyOz phases form, which are difficult to eliminate afterwards. With the design of contacts between the reactants PbO, (MgCO3).4Mg(OH2.4H2O and Nb2O5 we were able to control the reactions to get pure perovskite PMN in a single step. Powder mixtures homogenised at pH 10.0 upon heating at 900oC react to mixture of pyrochlore and perovskite. At pH 10.0, Pb-species and Nb2O5 have opposite surface charges as determined by zeta potential measurements and are therefore attracted. The formed contact surfaces favour the formation of lead niobate based pyrochlore. In contrast, at pH 12.5 the surface charges of Pb - and Nb- species are of the same sign and therefore repulse which is less favourable for the pyrochlore formation and pure perovskite phase is obtained. The formation of various aggregates as a function of pH is also confirmed by Monte Carlo simulation. Furthermore the ceramics prepared from this powder is sintered to 95 % of theoretical density at only 950oC, which is at least 200 K lower in comparison to conventional synthesis routes and exhibits excellent dielectric and electrostrictive properties.
9:00 PM - EE3.3
Direct Fabrication of La2Ti2O7 Film on Titanium Metal Substrate by Hydrothermal Method.
Chihiro Izawa 1 , Tomoaki Watanabe 1
1 Applied Chemistry, Meiji University, Kawasaki, Kanagawa, Japan
Show AbstractHydrogen has now attracted as future energy source. It is the most ideal way to produce hydrogen by using water splitting photocatalyst, which allow to generate hydrogen directly from sun light. The only early work on photocatalytic materials was TiO2 related materials. TiO2 is currently widely used as self cleaning materials, however the TiO2 is driven only under ultraviolet light irradiation. For visible light active water splitting photocatalysts are desirable from the viewpoint of efficient solar energy conversion into hydrogen. Recently,LaTiO2N has been demonstrated as an effective visible light active water splitting photocatalysts. However, no detailed photocatalytic mechanisms analysis has been reported. Therefore, investigation of the photocatalystic reaction mechanism of the LaTiO2N film on metal electrode should be important to improve the photocatalytic activities. The LaTiO2N film is prepared by nitriding of the La2Ti2O7 film. To fabricate LaTiO2N film on titanium substrate, in generally, La2Ti2O7 film on the titanium substrate is needed as a precursor film. However, to our best knowledge, there are no reports for synthesis of the La2Ti2O7 film on the metal substrate directly. Therefore, our target of this research is to synthesize the La2Ti2O7 film on titanium metal substrate. It is difficult, due to oxygen defect, to synthesize La2Ti2O7 film by RF sputtering or vapor deposition process. In this study, La2Ti2O7 films were synthesized by hydrothermal method with La(OH)3 solution at 300°C. The dependence of crystallinity, crystallite size, and dielectric properties of the products on the experimental parameters such as temperature, reaction time and additives has been studied.
9:00 PM - EE3.30
Engineering Oxygen Vacancy Defects on Ceria Nanotubes for Enhanced Catalytic Oxidation.
Neil Lawrence 1 , Joseph Brewer 1 , Lu Wang 2 , Jamie Wells-Kingsbury 1 , Wai-Ning Mei 2 , Chin Li Cheung 1
1 Chemistry, University of Nebraska-Lincoln, Lincoln, Nebraska, United States, 2 Physics, University of Nebraska at Omaha, Omaha, Nebraska, United States
Show AbstractOxygen vacancy defects (OVDs) play critical roles in influencing the catalytic activities of ceria. We report our study to modulate the density, and morphology of OVDs by applying low pressure thermal annealing in air and doping with very low gold content in ceria nanotubes. Transmission electron microscopy study revealed that three different types of OVDS were present in the ceria nanotubes. Compared to bulk and nanoparticle samples, ceria nanotube samples doped with 0.01 at.% of gold were found to have a much larger Ce3+/Ce4+ ratio in their chemical composition via x-ray photoelectron spectroscopy studies. These findings suggested that the density of OVDs in gold doped ceria nanotube catalysts was much higher that that of the bulk or nanoparticles with similar sample treatment. These gold doped nanotube samples were also found to have drastic increases in their oxidative catalytic activity towards carbon monoxide (CO) oxidation. The combined treatments of ceria nanotubes led to a large decrease in the T50 from 205 °C to 80 °C for CO oxidation. A postulated simulation model for the role of gold atom and small cluster dopants in the stabilization of OVDs in ceria nanotubes will be discussed.
9:00 PM - EE3.32
Metal and Non-metal Atoms Doping in Hematite as Photo-catalysts for PEC Hydrogen Production.
Muhammad Huda 1 , Aron Walsh 2 , Yanfa Yan 3 , Su-Huai Wei 3 , Mowafak Al-Jassim 3
1 Department of Physics, University of Texas at Arlington, Arlington, Texas, United States, 2 Chemistry, University College London, London United Kingdom, 3 , National Renewable Energy Laboratory, Golden, Colorado, United States
Show AbstractSemiconductor materials for economical photoelectrochemical (PEC) production of hydrogen using solar energy have attracted great attention since the demonstration of water splitting using a TiO2 photoanode illuminated with ultraviolet light almost forty years ago. α-Fe2O3 (hematite) has been considered a promising material that may potentially meet the PEC photo-catalysts criteria because of the following advantages: α-Fe2O3 is inexpensive, abundant, nontoxic, and stable in most alkaline electrolytes. It has a bandgap of 2.2 eV, which is capable of absorbing roughly 40% of the solar spectrum, leading to a maximum theoretical solar-to-hydrogen conversion efficiency of about 13% under AM1.5 illumination (the global standard spectral irradiance). However, despite these favorable characteristics, the maximum experimental solar-to-chemical efficiency reported in the literature for hematite is less than 3%. As α-Fe2O3 is a charge-transfer type insulator, the extremely low electrical conductivity and the indirect band gap (weak optical absorption) are the two most critical factors that limit the PEC performance of α-Fe2O3. Here we will present the band structures by first principle theories to better understand the conduction properties of α-Fe2O3, and also how to improve its performance by 3d transition metal atoms and group-III elements doping. All the calculations were done with density functional theory (DFT+U). We find that the incorporation of 3d transition metals in a -Fe2O3 has two main effects: (1) The valence and conduction band edges are modified. In particular, the incorporation of Ti provides electron carriers and reduces the electron effective mass, which will improve the electrical conductivity of α-Fe2O3. (2) The unit cell volume changes systematically: the incorporation of Sc increases the volume, whereas the incorporation of Ti, Cr, Mn, and Ni reduces the volume monotonically, which can affect the hopping probability of localized charge carriers (polarons). For non-metal atoms doping, while for Al-doping, the band gap remained almost the same, for Ga and In substitution the band gap marginally increased. However, increased conduction and PEC efficiency has been experimentally reported for Al-doped α-Fe2O3. It will be shown that here also the change in volume plays an important role in this behavior. Over all, even after group IIIA doping, the mechanism for charge conduction would be still small polaron hopping. A dramatic increase in photo-response cannot be expected for this type of doping in α-Fe2O3.
9:00 PM - EE3.33
Crystal Structure and Thermal Properties of Al6Ti2O13.
Stefan Hoffmann 1
1 Anorg. Chem., Max-Planck-Institut fuer Chemische Physik fester Stoffe, Dresden Germany
Show AbstractSystematic studies of the phase system Al2O3 – TiO2 by means of an arc-imaging furnace have recently revealed the crystal structure of the new compound Al6Ti2O13 [1]. It shows striking structural similarities to the well-known neighboring compound Al2TiO5 [2], which has received a considerable scientific interest due to its low thermal expansion and shock resistance [3]. Synchrotron powder X-ray diffraction (PXRD) studies in the range from 20 K to 1173 K (PXRD) proved the strong anisotropic thermal expansion of Al6Ti2O13 with an almost vanishing value along one axis. According to in situ high temperature PXRD the compound starts to decompose at higher temperatures into the binary oxides corundum and rutile, which react at about 1673 K and form the compound Al2TiO5. Additional high resolution synchrotron PXRD (Grenoble, beamline ID31) established a new modification of Al6Ti2O13 with a very small monoclinic distortion. Ref.: [1] S. T. Norberg, S. Hoffmann, M. Yoshimura, N. Ishizawa, Acta Crystallogr. C61 (2005) i35-i38. [2] A. E. Austin, C. M. Schwartz, Acta Cryst. 6 (1953) 812-813. [3] H. A. J. Thomas, R. Stevens, Br. Ceram. Trans. J. 88 (1989) 144-151.
9:00 PM - EE3.34
K3Ln[OB(OH)2]2[HOPO3]2 (Ln = Yb, Lu): Layered Rare-earth Dihydrogen Borate Monohydrogen Phosphates.
Yan Zhou 1 2 , Stefan Hoffmann 1 , Ya-Xi Huang 2 , Yurii Prots 1 , Walter Schnelle 1 , Prashanth Menezes 1 , Jin-Xiao Mi 2 , Ruediger Kniep 1
1 , Max-Planck-Institut für Chemische Physik fester Stoffe, Dresden Germany, 2 Department of Materials Science and Engineering, College of Materials, Xiamen University, Xiamen China
Show AbstractUntil recently the only compounds reported for the systems LnOx – B2O3 – P2O5 – (H2O) (Ln = rare earth) are given by Ln7O6[BO3][PO4]2 [1-3], which, however, are accessible by solid state reaction at high temperature only. We succeeded to synthesize two isotypic layered rare-earth borate phosphates, K3Ln[OB(OH)2]2[HOPO3]2 (Ln = Yb, Lu) by mild hydrothermal treatment of the appropriate educts at 453 K. The crystal structures were determined by single-crystal X-ray diffraction (R-3, Z = 3, Yb: a = 5.6809(2) Å, c = 36. 594(5) Å, V = 1022.8(2) Å3, Lu: a = 5.6668(2) Å, c = 36.692(2) Å, V = 1020.4(1) Å3). The overall crystal structure can be rationalized as consisting of two kinds of layers. One slab is K2Ln[HOPO3]2 similar to Glaserite (K3Na(SO4)2), which is composed of LnO6 octahedra connected with six PO4 tetrahedra by sharing common oxygen vertexes. Another is [OB(OH)2KOB(OH)2] which is composed of KO6 octahedra linked with six planar OB(OH)2 units. The two kinds of layers are stacked alternately along [001]. Field and temperature dependent measurements of the magnetic susceptibility of the Yb-compound revealed a paramagnetic behavior from 120 K to 400 K (4.84 μB). Magnetic ordering was not observed down to 1.8 K. Ref.: [1] Palkina, K. K.; Maksimova, S. I.; Chibiskova, N. T.; Dzhurinskii, B. F.; Gokham, L. Z. Izv. Akad. Nauk, Neorg. Mater. 1984, 20, 1063. [2] Shi, Y.; Liang, J.; Zhang, H.; Yang, J.; Zhuang, W.; Rao, G. J. Solid State Chem. 1997, 129, 45. [3] Ewald, B.; Prots, Yu.; Kniep, R. Z. Kristallogr. - New. Cryst. Struct. 2004, 219, 213.
9:00 PM - EE3.36
The (La0.7Ca0.3MnO3 - Mn3O4) Composite System: Remarkable Electrical and Magnetic Properties Below and Above the Percolation Threshold.
Benedicte Vertruyen 1 , Beatriz Rivas-Murias 1 2 , Jean-Francois Fagnard 1 3 , Philippe Vanderbemden 1
1 SUPRATECS, University of Liege, Liege Belgium, 2 Departamento de Química Física, Universidad de Santiago de Compostela, Santiago de Compostela Spain, 3 CISS, Royal Military Academy, Brussels Belgium
Show AbstractPolycrystalline manganites are known to exhibit low-field grain-boundary-related magnetoresistance in addition to the intrinsic colossal magnetoresistance. It has been shown that the extrinsic magnetoresistance may be enhanced by mixing the manganite with an insulating secondary phase. High temperature sintering of these composites, however, promotes ionic diffusion and usually results in a pronounced shift of the manganite composition and magnetic transition temperatures. In the present work, we report the synthesis and properties of a composite system that can be submitted to long sintering treatment without leading to significant modification of the manganite composition: the unique properties of the manganite/Mn3O4 system result from the fact that no compound with Mn/(La + Ca) > 1 exists in the composition, temperature and pressure ranges used during the synthesis. An additional advantage is the possibility to synthesize the composite samples in a single step by thermal treatment of a spray-dried precursor, instead of mixing pre-synthesized manganite and insulating powders. In the case of the La0.7Ca0.3MnO3/Mn3O4 series, a percolation threshold occurs for a La0.7Ca0.3MnO3 volume fraction of 20%. The dependence of the electrical resistivity can be described by percolationlike phenomenological equations. Below the percolation threshold (i.e., for conductive samples), we show that the resistivity vs. magnetic field curves display an unusual behavior below the Curie temperature of ferrimagnetic Mn3O4, due to local demagnetization field effects. Above the percolation threshold, the insulating character of the samples makes it possible to characterize the dielectric properties, which are found to be influenced by an external magnetic field.
9:00 PM - EE3.37
Phase Diagrams of BiFe1-xMnxO3+d and Bi1-xLaxFeO3.
Sverre Selbach 1 , Thomas Tybell 2 , Mari-Ann Einarsrud 1 , Tor Grande 1
1 Department of Materials Science and Engineering, Norwegian University of Science and Technology, Trondheim Norway, 2 Department of Electronics and Telecommunications, Norwegian University of Science and Technology, Trondheim Norway
Show AbstractChemical substitution of BiFeO3 enables tailoring of physical properties, crystal structures and phase transition temperatures. Mn and La are the most studied elements for substitution of Fe and Bi, respectively. Here we report the influence of chemical composition on the crystal structure, electronic properties and phase transitions of Bi1-xLaxFeO3 and BiFe1-xMnxO3+d. The crystal structure and phase transitions of BiFeO3 is strongly affected not only by Mn substitution, but also on the oxygen stoichiometry (3+d).[1] Depending on the synthesis conditions, a fraction of Mn3+ can be oxidized to Mn4+. This is charge compensated by oxygen hyperstoichiometry, inducing cation vacancies. BiFe0.7Mn0.3O3+d is demonstrated to undergo two structural phase transitions of first order with increasing temperature, first from the rhombohedral ferroelectric R3c to the orthorhombic paraelectric phase (Pbnm) at the ferroelectric Curie temperature Tc, and finally to cubic perovskite structure with space group Pm-3m.[2] Increasing Mn-content and oxygen hyperstoichiometry depresses the Néel temperature TN, and the temperatures of the two structural transitions.[1]Thermodynamic origins [3] of the ambient pressure solid solubility limit of xMn = 0.3 and challenges associated with chemical compatibility [4] of BiFeO3 towards supporting materials are also discussed.In the system Bi1-xLaxFeO3 the space group Pbnm (of pure LaFeO3) is found for x > 0.5, while for x < 0.5 the system goes through several single- and two-phase regions. La substitution strongly depresses the ferroelectric Tc, while mildly raising TN. Finally, phase diagrams for the systems BiFe1-xMnxO3+d and Bi1-xLaFeO3 are presented, establishing the stability regions of three, two, one and zero simultaneous ferroic properties, respectively. [1] S. M. Selbach, T. Tybell, M.-A. Einarsrud, T. Grande, Chem. Mater. 21, 5176 (2009).[2] S. M. Selbach, T. Tybell, M.-A. Einarsrud, T. Grande, Phys. Rev. B 79, 214113 (2009).[3] S. M. Selbach, M.-A. Einarsrud, T. Grande, Chem. Mater. 21, 169 (2009).[4] S. M. Selbach, T. Tybell, M.-A. Einarsrud, T. Grande, J. Solid State Chem. 183 (2010) 1205.
9:00 PM - EE3.38
Structure Property Investigations of Dy2MnCrO6.
Ganeshraj Chellappan 1 , Santhosh Nair 1
1 Low Temperature Physics Laboratory, Department of Physics, IIT MADRAS, Chennai India
Show AbstractDy2MnCrO6 was synthesized by solid state method. Rietveld refinement of X-ray powder diffraction data revealed that this compound crystallized in orthorhombic structure with Pnma space group, containing distorted (Cr/Mn) octahedra. We present here the correlations between the magnetic properties and the corresponding structural data collected at different temperatures. Dy2MnCrO6 shows magnetic ordering below 100K and the type of ordering exhibited by this system is investigated by ac and dc magnetic susceptibility measurements. The magnetic properties is explained with the well known super-exchange rules between the Mn and the Cr-ions.
9:00 PM - EE3.39
Graphene Oxide Framework (GOF) Materials: Theoretical Predictions and Experimental Results.
Jacob Burress 1 , Gadipelli Srinivas 1 2 , Jamie Ford 1 2 , Jason Simmons 1 , Wei Zhou 1 3 , Taner Yildirim 1 2
1 NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 2 Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States, 3 Materials Science and Engineering, University of Maryland, College Park, Maryland, United States
Show AbstractGraphene oxide chemistry has shown a recent resurgence in interest. Yet, there has been little attention paid to the gas storage capabilities of graphene oxide and graphene oxide based materials. We propose that by using the well-known chemistry between boronic acids and hydroxyl groups, graphene oxide layers can be linked together to form a new layered structure. This new nanoporous material, a so called graphene oxide framework (GOF), formed of layers of graphene oxide connected by benzene-boronic acid pillars is being investigated as a potential storage medium for hydrogen and other gases. Grand Canonical Monte Carlo adsorption simulations reveal that an idealized GOF structure could adsorb hydrogen up to 6 wt% at 77 K and 1 bar, a value higher than any other porous material known. Our initial synthesized GOF materials exhibit isosteric heats at zero coverage of 9 kJ/mol and 32 kJ/mol for H2 and CO2, respectively. The nitrogen BET surface area of these initial materials is around 500 m2/g. Despite this low surface area, GOFs exhibit 1 wt% H2 uptake at 1 bar. This is much less than what the ideal GOF structure can hold, suggesting that our initial GOF materials could be significantly optimized. Powder x-ray diffraction revealed tunable interlayer spacing, eventually reaching a maximum. Neutron spectroscopy studies of graphene oxide and GOFs with in-situ hydrogen loading have been performed. Results on the hydrogen dynamics in these systems will be presented. Additionally, GOF elemental composition has been determined via prompt gamma neutron activation analysis. In the future, GOF structures will be synthesized with tunable pore widths, volumes, and binding sites depending on the linkers chosen.
9:00 PM - EE3.4
Hydrothermal Synthesis and Characterisations of PerovskiteACrO3 (A= La, Pr, Sm, Gd, Dy, Yb, Ho, Lu and Y).
Kripasindhu Sardar 1 , Richard Walton 1
1 Department of Chemistry, University of Warwick, Coventry United Kingdom
Show AbstractIn an effort to find a common chemical route for the synthesis of perovskite rare-earth and yttrium orthochromites, a hydrothermal technique has been investigated. A single-source amorphous mixed hydroxide when heated in water under hydrothermal conditions is found to yield crystalline perovskite orthcohromites containing, La, Pr, Sm Gd, Dy, Yb, Ho, Lu and Y in a single step. A custom built hydrothermal apparatus designed to be operated to 500 oC has been employed in this purpose. The hydrothermal apparatus also enables to monitor temperature and pressure of the growth solution in-situ. It is observed that in order to obtain crystalline perovskite orthochromite materials, it is necessary to employ temperatures higher than 325 oC, which is beyond the temperature regime of conventional hydrothermal techniques (≤240 oC) and contrast with well documented studies of titanate, niobate and manganite perovskites[1]. The hydrothermally derived perovskite orthochromites have been analyzed using profile refinement of powder X-ray diffraction, Raman spectroscopy and magnetisation measurement. This shows high quality and purity of the samples. Additionally, some control over particle sizes and shape are evidenced to be possible by using different additives. The successful hydrothermal synthesis of perovskite oxides employing the present hydrothermal technique is note-worthy and the method may indeed be useful in practice in the areas such as solid oxide fuel cells, catalysis and multiferroics [2-4].References:(1) D. R. Modeshia and R.I. Walton Chem. Soc. Rev. 2010, 39 DOI:10.1039/b904702f.(2) G. A. Thompsett and N. M. Sammes, J. Power Sources, 2004, 130, 1.(3) M. Siemons, A. Leifert and U. Simon, Adv. Funct. Mater. 2007, 17, 2189.(4) C. R. Serrao, A. K. Kundu, S. B. Krupanidhi, U. V. Waghmare and C. N. R. Rao, Phys. Rev. B, 2005, 72, 220101(R).
9:00 PM - EE3.40
Structure-property Relations in Y3Al5O12:Ce and CaSc2O4:Ce Yellow Phosphors from Scattering and 27Al/45Sc NMR Studies.
Nathan George 1 , Ram Seshadri 2 , Bradley Chmelka 3
1 Chemical Engineering and Materials Research Laboratory, UCSB, Santa Barbara, California, United States, 2 Materials Department, Department of Chemistry and Biochemistry, and Materials Research Laboratory, UCSB, Santa Barbara, California, United States, 3 Chemical Engineering, UCSB, Santa Barbara, California, United States
Show AbstractSolid-state lighting systems consisting of a blue InGaN source in conjunction with a yellow phosphor are a promising way of creating efficient white light in systems that are long-lived and are durable. Efficient white LED lighting is often at odds, however, with the effective reproduction of the wide spectral gamut of sunlight i.e. a high color rendering index, CRI. The widely used and studied yellow phosphor, Y3Al5O12:Ce (YAG:Ce), is explored here using 27Al NMR and neutron pair distribution function studies. Changes in the 27Al spectra are monitored as a function of paramagnetic Ce3+ introduced into the YAG host lattice. 45Sc NMR of CaSc2O4:Ce are also discussed for the first time. In this relatively new phosphor system, the excitation and emission need to be further red-shifted in order for the CaSc2O4:Ce system to become useful with blue LED excitation and appropriate white light generation. 45Sc NMR results are combined with neutron pair distribution function data to relate structure and composition to quantum efficiency and excitation/emission spectra of the phosphors.
9:00 PM - EE3.41
pO2 Stability of Ba0.5Sr0.5Co0.8Fe0.2O3-δ.
Christian Niedrig 1 , Simon Taufall 1 , Holger Goetz 1 , Stefan Wagner 1 , Wolfgang Menesklou 1 , Stefan Baumann 2 , Ellen Ivers-Tiffee 1
1 Institut fuer Werkstoffe der Elektrotechnik (IWE), Karlsruhe Institute of Technology, Karlsruhe Germany, 2 Institut fuer Energieforschung (IEF-1), Forschungszentrum Juelich GmbH, Juelich Germany
Show AbstractThe mixed-conducting perovskite oxide Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF), given its outstanding oxygen ionic and electronic transport properties, is considered a promising material composition for oxygen transport membranes (OTM) operated at high temperatures. Its long-term stability under operating conditions is, however, still an important issue. Although the incompatibility of BSCF with CO2-containing atmospheres can be avoided by appropriate means (oxyfuel processes in the absence of carbon dioxide), the thermal as well as the chemical stability of BSCF itself are still under thorough investigation. This work is focused on the stability of BSCF in the targeted temperature range for OTM applications (700...900 °C) and in atmospheres with low oxygen contents. Previous studies in literature suggest limited chemical stability below oxygen partial pressures pO2 of around 10-6 bar. By employing a coulometric titration method based on a zirconia “oxygen pump” setup we were able to precisely control the oxygen partial pressure pO2 between 1 bar and 10-16 bar. Combining electrical measurements on dense ceramic bulk samples performed as a function of pO2 with an XRD phase composition study of single phase BSCF powders subjected to various pO2 treatments, an assessment of the chemical stability of BSCF is facilitated as a function of oxygen partial pressure. It could thus be shown that the pO2 stability limit is considerably lower than previously assumed in literature.
9:00 PM - EE3.42
Single Crystalline Zinc Structures Synthesized Spontaneously in Solution.
Seungho Cho 1 , Kun-Hong Lee 1
1 Chemical Engineering, Pohang University of Science and Technology (POSTECH), Pohang Korea (the Republic of)
Show AbstractWe report a method for the synthesis of Zn structures with a variety of morphologies through a spontaneous solution phase reaction without application of an electropotential under ambient conditions. We also describe, in detail, the influence of several experimental conditions on the morphology and microstructure of the Zn structures. The morphology of the Zn structures transitioned from hexagonal disks to dendritic forms as the reaction temperature was increased due to an increase in the driving force for Zn structure formation (over a temperature range from room temperature, 22°C, to 95°C). The size of the Zn structures was controlled by adjusting the concentration of zinc acetate dihydrate added to the reaction solution. When the concentration of zinc salt was reduced, smaller Zn structures were synthesized. Control experiments revealed that the aluminum layer, ammonia additions, and ammonia concentration were key factors for the formation of Zn metal structures. Zn nanowires were synthesized in the presence of thick Al layer. Based on these observations, we propose possible formation mechanisms for the spontaneous assembly of the various Zn structures.
9:00 PM - EE3.43
Ultra-fast Microwave Assisted Synthesis of Nanomaterials.
Keith Porter 1 , E. Barnhardt 1
1 Synthesis Division, CEM Corp, Matthews, North Carolina, United States
Show AbstractUntil the beginning of this decade, typical microwave (MW) reactions were conducted in domestic MW ovens. The advent of the dedicated MW system brought temperature and pressure control as well as greater safety features and reproducibility. In the beginning, common palladium catalyzed cross coupling reactions, such as Suzuki and the Heck reactions, were completed in just a fraction of the conventional reaction time. MW irradiation is now becoming widely used as a rapid heating method for the synthesis of inorganic nanoparticles due to the direct activation of the inorganic precursors which causes an increase in kinetics of nucleation and promotes particle uniformity and monodispersity. This work will focus on the benefits of MW irradiation for the synthesis of several different types of nanomaterials.
9:00 PM - EE3.44
Deviations from Vegard's Law in Ternary III-V Alloys.
Samuel Murphy 1 , Alexander Chroneos 1 , Chao Jiang 2 , Udo Schwingenschlogl 3 , Robin Grimes 1
1 Department of Materials, Imperial College London, London United Kingdom, 2 Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 3 PSE Division, KAUST, Thuwal Saudi Arabia
Show AbstractVegard's law states that, at a constant temperature, the volume of an alloy can be determined from a linear interpolation of its constituent's volumes. Deviations from this description occur such that volumes are both greater and smaller than the linear relationship would predict. Here we use special quasi-random-structures and density functional theory to investigate such deviations for MxN1-xAs ternary alloys, where M and N are group III species (B, Al, Ga and In). Our simulations predict a tendency, with the exception of AlxGa1-xAs, for the volume of the ternary alloys to be smaller than that determined from the linear interpolation of the volumes of the MAs and BAs binary alloys. Importantly, we establish a simple relationship linking the relative size of the group III atoms in the alloy and the predicted magnitude of the deviation from Vegard's law.
9:00 PM - EE3.45
Dehydrogenation and Regeneration of AB-BmimCl System.
Tessui Nakagawa 1 , Anthony Burrell 1 , Andrew Sutton 1 , John Gordon 1
1 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractAmmonia borane NH3BH3 (AB) is one of a number of strong candidates for a hydrogen storage material in automotive applications. AB still has three serious issues to overcome before it can be considered a useful storage material. These are somewhat slow hydrogen release kinetics, impurity gas emission, and reversibility. In order to improve AB performance, we investigated the dehydrogenation reactions of a mixture of AB and 1-butyl-3-dimethylimidazolium chloride (BmimCl), based upon the work of Seddon et al.. We selected an initial weight ratio of AB:BmimCl at 3:7. The result of differential scanning calorimetry showed that the dehydrogenation peak temperature of AB-BmimCl is 110 °C. The results of isothermal dehydrogenation measurement using burette system demonstrated that AB-BmimCl desorbs ~2 eq. of hydrogen with no (or only slight) foaming at 110 °C. At 90 °C, AB-BmimCl also desorbed 2 eq. of hydrogen over 110 minutes. The results of thermogravimetric analysis, infrared, and residual gas analysis revealed that the amount of the impurity gases desorbed from AB-BmimCl are slightly smaller than that of AB and gas desorption is almost completed by 120 °C. We have also examined the regeneration of AB-BmimCl after hydrogen desorption using hydrazine as the regenerating agent. Decoupled solution NMR results showed that the peak at ~-21 ppm, which corresponding to AB, recovered after regeneration, indicating regeneration of AB is successful. However, the resonance at ~30 ppm is associated with the BH3 carbene impurity. These results confirm that ionic liquid based ammoinia borane have potential for correcting some of the deficiencies associated with ammonia borane, but much more work is required.
9:00 PM - EE3.46
Synthesis and Characterization of New Topotactically-prepared Mixed-valance Titanates, KAxLa2Ti3O9.5 (A = K, Rb, Cs)
Kulugammana Gedera Ranmohotti 1 , John Wiley 1
1 Department of Chemistry and Advanced Materials Research Institute, University of New Orleans, New Orleans, Louisiana, United States
Show AbstractReductive intercalation of alkali-metals is an effective approach for electron-doping since electrons can be transferred from inserted metals to a host material. We describe the transformation of the Dion-Jacobson phase, KLa2Ti3O9.5, to the Ruddlesden-Popper phases, KAxLa2Ti3O9.5, (A = K, Rb, Cs) via alkali-metal intercalation through a low-temperature topotactic route. First, following the procedure of Gonen et al. (Inorg. Chem., 2006), K2La2Ti3O10 was combined with tetraphenyl-phosphonium bromide at 300 °C to produce KLa2Ti3O9.5. Reductive intercalation was then carried out by reacting the KLa2Ti3O9.5 phase with excess potassium, rubidium and cesium metal in evacuated Pyrex tubes at 290 °C, 250 °C and 290 °C, respectively. The increase in layer spacing due to the intercalation of the alkali-metals follows the order of the relative sizes, K< Rb < Cs. Since the intercalation step in KLa2Ti3O9.5 introduces unpaired electrons, magnetic susceptibility measurements on K1+xLa2Ti3O9.5 were performed. Field-cooled (FC) and zero-field cooled (ZFC) dc magnetic susceptibility curves split below 300 K. The temperature dependent susceptibility data at different fields were collected and they suggest magnetic ordering with a significant ferromagnetic component. Magnetization measurements as a function of field at different temperatures showed hysteresis. In this presentation, topochemical manipulation of KLa2Ti3O9.5 and the magnetic properties of K1+xLa2Ti3O9.5 will be presented and structure-property relationships discussed.
9:00 PM - EE3.47
First-principles Study of Structural and Elastic Properties of Monoclinic and Orthorhombic BiMnO3.
Zhi-Gang Mei 1 , Shun-Li Shang 1 , Yi Wang 1 , Zi-Kui Liu 1
1 Materials science and engineering, Penn State University, University Park, Pennsylvania, United States
Show AbstractThe structural and elastic properties of BiMnO3 with monoclinic (C2/c) and orthorhombic (Pnma) ferromagnetic (FM) structures have been studied by first-principles calculations within the LDA+U and GGA+U approaches. The equilibrium volumes and bulk moduli of BiMnO3 phases are evaluated by equation of state (EOS) fittings, and the bulk properties predicted by LDA+U calculations are in better agreement with experiment. The orthorhombic phase is found to be more stable than the monoclinic phase at ambient pressure. A monoclinic to monoclinic phase transition is predicted to occur at pressure about 10 GPa, which is ascribed to magnetism vs. volume instability of monoclinic BiMnO3. The single-crystal elastic stiffness constants cij’s of the monoclinic and orthorhombic phases are investigated using the stress-strain method. The c46 of the monoclinic phase is predicted to be negative. In addition, the polycrystalline elastic properties including bulk modulus, shear modulus, Young’s modulus, bulk modulus/shear modulus ratio, Poisson ratio, and elastic anisotropy ratio are determined based on the calculated elastic constants. The presently predicted phase transition and elastic properties open new directions for investigation of the phase transition in BiMnO3, and provide helpful guidance for the future elastic constant measurements.
9:00 PM - EE3.5
Changes in Optical Absorption and Tb3+ Luminescence Due to the Variation of Tb3+ and Ag Co-dopants in Li2O-LaF3-Al2O3-SiO2 Glass.
P. Piasecki 1 , A. Piasecki 1 , Z. Pan 1 , S. Morgan 1 , R. Mu 1
1 Physics, Fisk University, Nashville, Tennessee, United States
Show AbstractTb3+ and Ag co-doped Li2O-LaF3-Al2O3-SiO2 (LLAS) glasses were synthesized via melt-quenching technique. Optical absorption was used to confirm the presence of Ag nanoparticles (NPs); NP size was modified by heat treatment-driven nucleation. The interaction between Tb3+ ions and Ag NPs was compared for two types of co-doping: variation of Ag with Tb3+ held constant, and variation of Tb3+ with Ag held constant. Photoluminescent excitation/emission and absorbance were studied. Two competitive effects were seen with variation of dopant concentrations and annealing times: the enhancement/quenching of Tb3+ luminescence and the growth of the Ag absorbance band about the Surface Plasmon Resonance wavelength (420 nm). The wavelength-specific quenching of emission intensity with Ag NP growth suggests the existence of an energy transfer-based relaxation process from the excited Tb3+ ions to the Ag NPs. Changes in the optical absorbance and photoluminescence were noted both for variation of dopants and for variation of annealing times.
9:00 PM - EE3.6
Glassy and Crystalline APSe6 (A = K, Rb) Thin Films Exhibiting Strong Second-order Nonlinear Optical Responses via a Solution-based Deposition Process.
In Chung 1 , Joon I. Jang 2 , John Ketterson 2 , Mercouri Kanatzidis 1
1 Chemistry, Northwestern University, Evanston, Illinois, United States, 2 Physics and Astronomy, Northwestern University, Evanston, Illinois, United States
Show AbstractWe present highly crystalline and glassy thin films of promising infrared second-order nonlinear optical (NLO) materials of KPSe6 (χ(2) = 151.3 pm/V) and RbPSe6 (χ(2) = 149.4 pm/V) via a solution-based deposition process. The compounds are soluble in a polar solvent of N2H4. The resulting solutions can be deposited by a spin coating process to give uniformly transparent, glassy thin films of those materials. As-prepared glassy films exhibited strong, intrinsic second harmonic generation (SHG) responses over a wide range of wavelengths through an infrared and visible region. Highly crystalline, optically transparent APSe6 (A = K, Rb) thin films can be readily obtained by annealing the corresponding glassy films at 215 - 230 °C for 5-10 min since they can reversibly switch between crystal and glass states. The crystallized thin films exhibited significantly enhanced SHG and difference frequency generation (DFG) responses. We propose that this approach can be widely applied to fabricate stable NLO glassy and crystalline thin films using materials that undergo a phase-change behavior.
9:00 PM - EE3.7
A Computational Study into the Role of Defects in BaTiO3.
James Dawson 1 , Ben Bin 1 , Colin Freeman 1 , John Harding 1 , Derek Sinclair 1
1 Department of Engineering Materials, University of Sheffield, Sheffield United Kingdom
Show AbstractIt is well known that the BaTiO3 perovskite structure can accommodate a wide range of both isovalent and aliovalent dopant ions and that these dopant ions have a significant effect on the electrical properties of the material. For instance, a small concentration of La on the Ba-site has a dramatic effect on resistivity and causes the material to exhibit n-type semiconductivity, however when the La concentration is increased the material becomes insulating [1]. XRD has been used to establish ternary phase diagrams for Rare Earth (RE3+) ion doping of BaTiO3 and to gain insightful information on solid solution limits and substitution sites. Large rare earth ions, such as La have been found to exclusively dope at the Ba-site with a large solid solution limit (up to 25%). Intermediate sized cations such as Gd, show very limited Ba or Ti-site solubility; yet show extensive solid solutions (up to 20%) according to a self-compensation mechanism, i.e. RE3+ substitution at both the Ba2+ and Ti4+ sites. Small dopants such as Yb, doped exclusively on the Ti-site with a solid solution limit of up to 5% for the cubic phase and between 5% and 15% for the hexagonal phase. Isovalent dopants such as Ca2+ and Sr2+ on the Ba-site are also common. A solid solution limit of 100 mol% exists for Sr2+, but only a 25% limit for Ca2+ due to the size mismatch [2]. Such dopant ions are known to have a significant effect on the Tc of BaTiO3. Atomistic methods have been used to study the defect chemistry of BaTiO3 at both the dilute limit and beyond. New Ba-O and Ti-O interatomic potentials have been created and calibrated against ab initio simulations. Both cubic and hexagonal phases have been considered. Numerous dopant incorporation methods have been studied for RE3+ incorporation and excellent correlation with experimental findings has been observed. Exploration of solid solutions for Ca2+, Sr2+ and RE3+ ions in BaTiO3 have also been carried out. We also discuss the implications for the method of semiconductivity in the material based upon the energetics of the dopant incorporation mechanisms. References1. Jonker G. H., Some aspects of semiconducting barium titanate, Solid-State Electron., 1964, 7 (12): p. 895-903.2. Matra D., Ferroelectric ceramics, 1966, London: Maclaren and Sons Ltd.
9:00 PM - EE3.9
Design of New Complex Layered Oxychalcogenides and Oxyhalides as Potential Electronic and Ionic Materials.
Ardak Kusainova 1 , Patrick Woodward 2
1 , science fund, Astana Kazakhstan, 2 Chemistry, Ohio State University, Columbus, Ohio, United States
Show AbstractA systematic search of new physically functional materials is focused on two crystallochemical families with layered structures: complex oxychalcogenides and complex oxyhalides. To design new materials we use the principles of structural chemistry. Particular interest is placed in new crystallochemical families with layered structure as MOCuX family, where M=Bi, RE, X=S, Se, Te and BIPOX (bismuth perovskite oxyhalides) class with non-centrosymmetric (optically active) structure. Both types of structures open a new way of investigation for the same reason as the related families of Sillen and Aurivillius phases. In recent years more then 19 members of new crystallochemical family of oxychalcogenides with general formula (MO)(TX) where M=Bi, Pb, T=Cu, Ag, X=S, Se, Te such as LaOAgS (M. Palazzi etc// Acta Crystallogr, Sect. B.37, 1981, 1337), BiOCuS (L.Kholodkovskaya etc// EPDIC-2, Materials Science Forum, vv133-136, pp 958, 1993 and A.M.Kusainova etc// J. Solid State Chem., 1994,112,p. 189-191) have been prepared and characterized by powder X-ray diffraction. First members have shown good superionic and electronic properties. Recently some interest to this class of materials has increased owing to the observation of high-Tc superconductivity in isostructural and doped compound LaOFeAs (KamiharaY etc// J.Am.Chem.Soc, 130 (11), March 19, 2008).In a BIPOX family, new integrowth phases can be made by stacking fluorite-perovskite-halide layers of differing “thickness”. It has been shown that BIPOX members with one, two or three perovskite layers possess ferroelectric properties(A.M.Kusainova etc// J. Mater. Chem. , 2002, 12, pp.3413-3418).
Symposium Organizers
P. Shiv Halasyamani University of Houston
David G. Mandrus The University of Tennessee/Oak Ridge National Laboratory
Kyoung-Shin Choi Purdue University
Simon J. Clarke University of Oxford
EE4: Solid State Materials and Energy
Session Chairs
Simon Clarke
G. Jeffrey Snyder
Tuesday AM, November 30, 2010
Ballroom A, 3rd floor (Hynes)
9:30 AM - **EE4.1
Materials and Energy; Processing, Storage and Conversion.
Duncan Gregory 1
1 Chemistry, Univeristy of Glasgow, Glasgow United Kingdom
Show AbstractIf society is to overcome many of the environmental and economic challenges that are emerging in the 21st century, then finding sustainable energy solutions is imperative. Materials chemistry is central to addressing these challenges; not least in providing ways in which we can harness energy and convert it while also supplying means to store it and effectively transport it as a vector. Further one needs to consider how one might develop new processing routes to important materials that could consume considerably less energy than those in use today, while remaining economically viable.This lecture considers some of these materials chemistry topics drawing on examples from our work, including lithium ion batteries, hydrogen storage materials, thermoelectrics and sustainable materials processing. The importance of new compounds and new synthesis approaches is discussed in relation to designing materials with improved functionality.
10:00 AM - EE4.2
A Computational Investigation of Alkali Metal Borohydrides and Amidoboranes for Hydrogen Storage.
Philippe Aeberhard 1 2 , Keith Refson 2 , Peter Edwards 1 , William David 2 1
1 Department of Chemistry, University of Oxford, Oxford United Kingdom, 2 ISIS Facility, Rutherford Appleton Laboratory, Chilton, Oxfordshire, United Kingdom
Show AbstractThe development of materials for the safe and efficient storage of hydrogen is regarded as the crucial barrier for an energy economy based on hydrogen instead of fossil fuels to become reality. Many chemical hydrides of light elements (alkali metals, alkaline-earth metals, first and second row elements) offer great promise for hydrogen storage at the operating temperatures of fuel cells (ca. 80°C); however, almost all potential hydrogen storage materials with an attractive storage capacity suffer from irreversibility of the hydrogen desorption/absorption reaction and high kinetic barriers to thermal desorption. After hydrogen desorption, it is difficult and, most often, practically not viable to rehydrogenate the products. Despite the practical importance of reversibility, surprisingly little is known about the desorption mechanisms in many key systems. In order to be able to improve the desorption properties, it is important to develop a detailed understanding of the dehydrogenation reaction – kinetics, thermodynamics, structural changes, and reaction mechanism.We undertake ab initio studies of several important complex metal hydrides in the solid state using density functional theory (DFT) based methods. The systems studied include lithium and sodium borohydride (LiBH4 and NaBH4), and lithium and sodium amidoborane (LiNH2BH3 and NaNH2BH3). We study the crystal structures and dynamical disorder of these systems at both ambient temperature and near the decomposition temperature using DFT and ab initio molecular dynamics (AIMD) simulations, and determine plausible decomposition reaction pathways in the crystalline phase. The AIMD simulations at various temperatures show that the large amplitude motions of the metal atoms as the systems are heated up are important for inducing hydrogen release; however, even though the metal ion mobility is an important factor in the decomposition reaction mechanism, the reaction-inducing step is the breakage of a B-H bond in all systems studied. Calculations show that the metal ion is unable to abstract this hydrogen atom, consistent with the experimentally observed high ionic mobility of Li and high desorption temperature of LiBH4. The reaction mechanisms for hydrogen release are revealed using the nudged elastic band (NEB) and metadynamics methods for NaBH4 and LiNH2BH3.
10:15 AM - EE4.3
First-principles Modeling of Diffusion Reactions in the Dehydrogentation of NaAlH4.
Kyle Michel 1 , Vidvuds Ozolins 1
1 Materials Science and Engineering, University of California, Los Angeles, Los Angeles, California, United States
Show AbstractIt has been proposed in experimental studies that diffusion of metal species may be the rate limiting step in various hydrogen storage reactions. However, a theoretical model has yet to be developed that adequately explains the underlying processes that are involved. Here we present such a model within the framework of a diffusion reaction and apply it to the dehydrogenation of NaAlH4. Using density functional theory, the concentration gradients and diffusivities of native charged and neutral defects in NaAlH4 and Na3AlH6 are calculated. From this, the flux of each defect type is obtained for simple, model systems and subsequently the activation energy for the diffusion reaction is found. We find that this activation energy matches well to that which has been obtained in experimental work for the dehydrogenation of Ti-doped NaAlH4, showing that diffusion of metal species is likely the rate limiting process in this reaction. The model that is presented can easily be applied to other diffusion reactions that occur in the solid state.
10:30 AM - EE4.4
Voltage Dependence of Bulk Resistivity in BaTiO3:Mg.
Colin Freeman 1 , John Harding 1 , Tony West 1
1 Engineering Materials, University of Sheffield, Sheffield United Kingdom
Show AbstractBarium Titanate has a range of exciting properties such as ferroelectricity and a high dielectric constant that make it a valuable commerical material. The electrical properties of BaTiO3 are obviously crucial to its uses and much effort is placed in their modification. Ceramics of BaTiO3 with Mg and Zn doping onto the Ti site have a modest semiconductivity who value is significantly increased a hundred-fold with the application of a small dc bias voltage [1]. A result not seen in undoped BaTiO3. This dc-depedent behaviour has been observed within the grains and at the grain boundaries and therefore has been linked to the defect chemistry of the system.We present classical and ab initio simulations of the defect region around the Mg dopant. These simulations analyse the likely compensation mechanisms within the bulk material and the segregation/binding of the defects within the structure. The simulations give details of the physical and electronic strucutre of the defect region. The interplay between both of these characteristics plays an important role in the properties of the defect and we demonstrate how these link into the unusual resistivity behaviour of the bulk material.[1] H. Beltran, M. Prades, N. Maso, E. Cordoncillo, A.R. West, J. Am. Ceram. Soc., 93 (2010), 500
11:15 AM - **EE4.5
NMR Studies of Local Structure, Cation Ordering and Protonic Conduction in Perovskites.
Clare Grey 1 2 , Lucienne Buannic 1 , Frederic Blanc 1 , Derek Middlemiss 1
1 , Stony Brook University, Stony Brook, New York, United States, 2 Chemistry, Cambridge University, Cambridge United Kingdom
Show AbstractThis talk will illustrate the use of high field, multinuclear NMR spectroscopy to investigate the nature of the defects in materials for solid-state electrolytes. In particular, we focus on electrolytes that operate via protonic conduction in solid oxide fuel cells. For example, the cations in BaZrO3 or BaSnO3 can be substituted by either Y3+ or Sc3+ to create oxygen vacancies. These vacancies can be filled with H2O, the water molecules dissociating to form mobile ions that contribute to the long-range ionic transport in these systems. NMR experiments are used to examine the local structure, the locations of the vacancies and how this affects protonic/oxygen ion motion in these systems. NMR studies of the host B cations (Zr, Sn) can be used to quantify (particularly in the case of Sn) the ratio of 5:6 fold cations, and thus indirectly, the location of the vacancy. NMR studies of the substituents (Sc, Y) can be used to investigate vacancy trapping. The location of the substituent ion is often ambiguous, and we show that 89Y can be used to investigate cation doping on the A vs. B site of the perovskite, the former reducing the number of oxygen vacancies and thus the number of protons, following hydration. Finally, 17O NMR experiments are shown to be extremely sensitive to the nature of the B cation directly bound to the oxygen site, different resonances being observed for the B-O-B’ sites following Y/Sc doping. Chemical shift calculations, performed by using the CASTEP code, reveal that oxygen ions in axial and equatorial positions relative to a vacancy (i.e., in a OaxialB(Oeq)-vac local environment, where vac = oxygen vacancy) can be distinguished in related systems. The implications of these results for protonic conduction will be discussed.
11:45 AM - **EE4.6
Electrodeposition as a Synthetic Tool for Solid State Energy Storage Materials.
Amy Prieto 1 , James Mosby 1 , Derek Johnson 1 , Matthew Rawls 1
1 Chemistry, Colorado State University, Fort Collins, Colorado, United States
Show AbstractWe are using electrodeposition as the main synthetic tool for the fabrication of a three-dimensional (3D) lithium-ion rechargeable battery. The proposed battery architecture offers the possibility of higher power density and longer cycle life. We are incorporating electrodeposited Cu2Sb, an interesting anode material, into integrated 3D battery architectures. Electrodeposition of the anode and subsequent electrolyte coatings is key to the final three-dimensional architecture, and is a low cost, scalable fabrication approach. We will present two architectures, one based on a nanowire array and one based on high surface area foams. First, cycling data will be shown demonstrating that the nanostructured Cu2Sb shows significantly enhanced capacity retention over the bulk material after many cycles. Second, the electrodeposition of ultra thin, conformal coatings of separator materials directly onto the Cu2Sb anode electrode will be illustrated. This is achievable because the anode material is electrically conducting. Battery performance of these composite structures will also be presented.
12:15 PM - EE4.7
Preparation and Ionic Conductivity of Dense Magnesium Titanium Phosphates.
Hiroo Takahashi 1 , Hitoshi Takamura 1
1 Department of Materials Science, Tohoku University, Sendai Japan
Show AbstractRechargeable batteries are of great interest because of use in a variety of commercial applications such as electric vehicles. To make them safer and more versatile, a number of novel materials have been developed. One of the solutions is to use magnesium, which is full of resources, environmental friendly and easy to handle. To realize such the Mg-ion battery, cathode materials having high capacity and mobility of Mg-ion are highly demanded. In this study, we focus on magnesium titanium phosphates showing high cation nonstoichiometry and conductivity. Mg0.5Ti2(PO4)3 has reportedly shown a Mg-ion conductivity of 2.47 × 10-5 S/cm at 873 K; however, because of its poor sinterbility, it is difficult to separate its bulk and grain boundary conductivities. Moreover, its Mg-ion conductivity might have been undervalued. The purpose of this study is to prepare dense magnesium titanium phosphates by utilizing high pressure on the order of giga-pascal and optimizing sintering conditions, and to evaluate their ionic conductivity. Mg0.5Ti2(PO4)3 is prepared by using sol-gel method. The resultant powder is sintered at 1073-1473 K for 2-24 h under air, or treated at 1073-1273 K under 6 GPa. To evaluate electrical conductivities, AC impedance analysis is performed in the frequency range of 0.01 Hz to 10 MHz. The relative density of Mg0.5Ti2(PO4)3 sintered at 1473 K increases up to approximately 80 %; while, Mg0.5(TiO)PO4 is formed as a second phase. For this sample, three depressed semicircles are observed. Judging from the magnitude of capacitances (10-11, 10-9, 10-8 F), these semicircles are attributed to bulk, grain boundary, and electrode responses, respectively. The ionic conductivity calculated from the bulk resistance is higher than the reported value of Mg0.5Ti2(PO4)3 by two to three orders of magnitude. By pressing the Mg0.5Ti2(PO4)3 powder at 1073 K under 6 GPa, a relative density of 90 % is attained. Moreover, a novel high-pressure phase is formed. In the presentation, their electrical conductivity will be discussed in the context of their density, grain size, and crystal structure.
12:30 PM - EE4.8
Synthesis and Characterization of Mesoporous Tungsten-doped Titanium Dioxide for Electrocatalytic Applications.
Juho Song 1 , Francis DiSalvo 2 , Ulrich Wiesner 3
1 School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, New York, United States, 2 Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York, United States, 3 Department of Materials Science and Engineering, Cornell University, Ithaca, New York, United States
Show AbstractTungsten-doped titanium dioxide is a conducting metal oxide and chemically stable at very acidic conditions (pH 0~2) which makes it a potential alternative to conventional carbon supports for PEM fuel cell electrodes. The self-assembly of block copolymers with inorganic precursors is a well-known approach toward highly ordered mesoporous materials which generally enhance electrocatalytic activity. Despite advances in the field, it is still a challenge to synthesize mesoporous tungsten-doped titanium dioxide without collapse of the pore structure. In this work, we report the one-pot synthesis of mesoporous tungsten-doped titanium dioxide through the self assembly of block copolymers with titanium and tungsten precursors followed by post-processing techniques. After materials characterization we investigate the electrochemical performance of the resulting mesoporous and doped materials.
EE5: Thermoelectrics and Related Materials
Session Chairs
Tuesday PM, November 30, 2010
Ballroom A, 3rd floor (Hynes)
2:30 PM - **EE5.1
Unusual Thermopower of Complex 4d Oxides.
Ichiro Terasaki 1
1 Physics, Nagoya University, Nagoya Japan
Show Abstract4d Transition-metal oxides are interesting in the sense that the band width is often comparable with the electron-electron correlation. As a result, unusual physical properties can arise from the interplay between the itinerancy and the localization. The p-wave superconductivity in Sr_2RuO_4 and the Mott transition in Ca_2RuO_4 are prime examples. We have studied the thermopower of various Ru- Rh- and Pd-oxides, and revealed how the anomaly in the thermopower can be understood in terms of characteristic electronic states on the 4d transition-metal ions. In this talk, we will show three examples for the anomalous thermopower in the complex 4d transition-metal oxides; (i) The sign change in the thermopower of Ru-doped LCu_3Ti_4O_12, (ii) the thermopower independent of carrier-density in CuRhO_2, (iii) ambipolar doping in CaPd_3O_4.
3:00 PM - **EE5.2
Thermoelectric Properties of New Thallium Tellurides.
Savitree Bangarigadu-Sanasy 1 , Cheriyedath Sankar 1 , Holger Kleinke 1
1 Department of Chemistry, University of Waterloo, Waterloo, ON, Ontario, Canada
Show AbstractThermoelectrics (TE) may be used to convert a thermal gradient into electricity (Seebeck effect: power generation) or vice versa (Peltier effect: cooling). For example, TE materials may be employed to recover part of the energy from the waste heat of the exhaust gases of automotives. By reducing the alternator load on the engine, this energy recovery with current state-of-the-art thermoelectrics may lead to fuel economy improvements of about 5%.
In addition to, e.g., bismuth and lead tellurides, various Zintl compounds, antimonides and clathrates, some thallium containing tellurides are known to have outstanding thermoelectric properties as well. For example, doping PbTe with Tl leads to an excellent ZT = 1.5 at 773 K [1], and Tl9AgTe5 has ZT = 1.2 at 700 K, mostly because of its low thermal conductivity [2]. As exploratory materials chemists, we are now investigating various ternary systems Tl/M/Te, attempting to identify new thermoelectric materials. For example, we uncovered the new tellurides Tl4MTe4 with M = Zr, Hf, which adopt a new complex structure type with weak Tl–Tl bonding extended along all three directions. Holes in this structure may be partially filled, e.g. with Zr atoms, which are only loosely bound to the six surrounding Te atoms like the filler atoms in the filled skutterudites or clathrates [3].
[1] J. P. Heremans, V. Jovovic, E. S. Toberer, A. Saramat, K. Kurosaki, A. Charoenphakdee, S. Yamanaka and G. J. Snyder, Science, 2008, 321, 554.
[2] K. Kurosaki, A. Kosuga, H. Muta, M. Uno and S. Yamanaka, Appl. Phys. Lett., 2005, 87, 061919.
[3] C. R. Sankar, S. Bangarigadu-Sanasy, A. Assoud and H. Kleinke, J. Mater. Chem., 2010, in press.
3:30 PM - **EE5.3
Zintl Chemistry for Designing High Efficiency Thermoelectric Materials.
Jeff Snyder 1
1 G Jeffrey Snyder, Caltech, Pasadena, California, United States
Show AbstractZintl phases and related compounds are promising thermoelectric materials, for instance high zT has been found in Yb14MnSb11, clathrates and the filled skutterudites. The rich solid-state chemistry of Zintl phases enables numerous possibilities for chemical substitution and structural modifications that allow the fundamental transport parameters (carrier concentration, mobility, effective mass, and lattice thermal conductivity) to be modified for improved thermoelectric performance. For example, free carrier concentration is determined by the valence imbalance using Zintl chemistry, thereby enabling the rational optimization of zT. The low lattice thermal conductivity found in complex structures with large unit cell volumes is generally due to the high fraction of low velocity optical phonon modes. Despite their complex structures and chemistry, the transport properties of many modern thermoelectrics can be understood using traditional models for heavily doped semiconductors.
4:00 PM - EE5: Energy
BREAK
4:30 PM - EE5.4
Formation and Physical Properties of Compounds with Supercell Structure of Normal Half-heusler Phase.
Ding-Bang Xiong 1 2 , Norihiko Okamoto 1 , Shunta Harada 1 , Katsushi Tanaka 1 , Kishida Kyosuke 1 , Harayuki Inui 1
1 Department of Materials Science and Engineering, Kyoto University, Kyoto Japan, 2 Department of Chemistry, Philipps University Marburg, Marburg Germany
Show AbstractA family of compound with supercell structure of normal half-Heusler phase were obtained via high-temperature reaction from elements in stoichiometric ratios in M-Zn-Sb (M=Fe, Ru, Co, Rh) and Ir-Zn-Sn ternary system. The formation of this type of supercell structure was controlled by valence electron concentration per unit cell. Around stoichiometric ratio 1:1:1, the phase width of this supercell structure is wide in some directions in phase diagram, but slight variation of some element in the other direction results in the change of structure, leading to other 1:1:1 phases with anti-PbFCl-type or normal half-Heusler structures. The potential of the undoped or doped compounds as thermoelectric materials was assessed by measuring transport properties (including electrical resistivity, Seebeck coefficient, and thermal conductivity) above room temperature. The Ru-Zn-Sb and Ir-Zn-Sn systems show typical metallic behaviors, but the thermal conductivity at room temperature of Ru-Zn-Sb phase is low and about one quarter of many normal half-Heusler phases. The normal half-Heusler phase in Co-Zn-Sb system show high electric resistivity but low Seebeck coefficient, which could attributed to the contrary contributions from two types of charge carriers. The electric resistivity was decreased in the supercell structure in Co-Zn-Sb system. Its Seebeck coefficient is in moderate scale, and the antisite disorders in zinc-rich side decrease the thermal conductivity by 30% compared with the phase with partial occupied sites. The investigations on magnetic properties were carried out on Fe-Zn-Sb and Co-Zn-Sb systems. Anti-PbFCl-type structure in Fe-Zn-Sb system shows two-dimensional magnetic Fe atomic layer, in which there are two magnetic transitions, one is the intra-layer interaction below 260 K and the other one is the inter-layer interaction below 50 K. Co-Zn-Sb phase with supercell structure is ferromagnetic compound with Curie temperature at about 310 K.
4:45 PM - **EE5.5
Layer-by-layer Design and Synthesis and Precision Oxygen-engineering of Novel/Tailored Oxide Materials for Energy Technologies.
Maarit Karppinen 1 , Hisao Yamauchi 1
1 Department of Chemistry, Aalto University, Espoo Finland
Show AbstractTransition metal oxides play central roles in many important future energy technologies. The apparent examples include the next-generation thermoelectric devices based on cobalt oxides, solid-oxide fuel cells based on a tailored combination of various oxide materials, Li-ion batteries based on oxides of cobalt, manganese, iron, titanium, etc., and high-Tc superconductors based on copper oxides. Moreover, smart oxide materials are sought for the storage and/or separation of the related utility gases, such as hydrogen and oxygen. A majority of (multi)functional oxide materials to be potentially employed in the emerging energy technologies possess – in common – a (multi)layered crystal structure and nonstoichiometry in terms of oxygen. Hence atomic-level layer-engineering and oxygen-engineering techniques are indispensable to expand the material frontier and to shape the new materials into optimal performance.Here we demonstrate the powerfulness of concepts of homologous series and layer-engineering, originally developed for copper-oxide superconductor research, in the design and synthesis of various members of the cobalt-oxide family, [MmArOm+r]q[CoO2]. The “double zero” (m=0, r=0) member of the series, i.e. CoO2, has quite interestingly turned out to be a paramagnetic metal. The next simplest members, i.e. the “single-zero” (m=0) structures cover not only the Li-ion battery cathode material, LixCoO2 (r=1) and the first thermoelectric oxide material, NaxCoO2 (r=1), but also the r=2 compounds, [(Sr/Ca)2O2]q[CoO2], that possess the parent structure of the misfit-layered thermoelectrics, e.g. [CoCa2O3]q[CoO2] (m=1, r=2) and [Bi2(Sr/Ba)2O4]q[CoO2] (m=2, r=2). For the sample synthesis state-of-the-art approaches, such as electrochemistry, encapsulation and ultra-high pressure techniques, have been employed. On top of that, the materials have been tailored in terms of doping for optimal performance through precision oxygen-engineering techniques.We moreover discuss our recent efforts of enhancing the thermoelectric properties of [CoCa2O3]q[CoO2] through nanostructuring by the atomic-layer-deposition (ALD) thin-film coating technique. The ALD technique is unique in the sense that it is based on saturative surface reactions of alternately supplied precursor vapours such that the film growth is self-limiting. This provides us with several practical advantages, such as atomic level control of both the film composition and thickness, perfect step coverage and large-area uniformity. In other words, the ALD technique facilitates by its nature the growth of perfectly conformal coatings on variously (nano)structured surfaces.
5:15 PM - EE5.6
Structure-property Relationships in Type I and II Si Clathrates.
Stevce Stefanoski 1 , Matthew Beekman 2 , George Nolas 1
1 Physics, University of South Florida, Tampa, Florida, United States, 2 Chemistry, University of Oregon, Eugene, Oregon, United States
Show AbstractClathrates comprise a group of "open-framework" materials in which covalently-bonded atoms form frameworks sequestering "guest" atoms. These materials are being actively investigated because of their potential for a range of applications, including solid state energy conversion, optoelectronic, and superconductivity. Type I and II Si clathrates with Na as guest atoms have long been known. Both types have been obtained as microcrystalline powders through a degassing process, and recently singles have been obtained using Spark Plasma Sintering. Very recently we employed a novel synthetic route and obtained single crystals of both structure types. This offers the possibility of investigating the intrinsic physical properties of these materials as they are strongly dependent on their structure and stoichiometry. Stoichiometric type I and II clathrates possess metallic conduction; however, semiconducting type II clathrates may be obtained by varying the guest content. The structure-property relationships are discussed from both microcrystalline powder and single crystal specimens of Na-containing type I and II Si clathrates.
5:30 PM - **EE5.7
Molecular Dynamics Study of Dielectric Response in a Relaxor Ferroelectric.
Ilya Grinberg 1 , Young-Han Shin 1 , Andrew Rappe 1
1 Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania, United States
Show AbstractPolar oxides with chemical formula ABO3 and the perovskite crystal structure offer high electromechanical coupling, leading to their use as piezoelectric materials. In many cases, these systems are solid-state solutions of antiferroelectric and ferroelectric materials. The highest piezoelectric response comes from solutions with one component that is a “relaxor ferroelectric.”Unlike normal ferroelectrics, which exhibit Curie-Weiss behavior and a narrow peak in dielectric constant at the phase transition temperature, relaxor ferroelectrics show elevated dielectric response over hundreds of kelvins, making them extraordinarily useful for real-world applications such as next-generation Naval SONAR. Further exploration of this class of materials is hampered by the complex behavior of relaxors, which is thought to arise from poorly-understood “polar nanoregions.”We use atomistic molecular dynamics simulations to study relaxor behavior in the 0.75 PbMg1/3Nb2/3O3-0.25 PbTiO3 material. Even for a fairly small simulation size of 1000 atoms, the system exhibits frequency dispersion and deviation from the Curie-Weiss law typical of relaxor materials. Analysis of the time autocorrelation functions for individual atoms allows us to identify the Nb atoms with a high concentration of neighboring Ti atoms as the nucleation sites for the relaxor behavior. This is due to the higher coupling between the cation displacements induced by the presence of overbonded oxygen atoms.
EE6: Poster Session: Solid State Inorganic Materials Chemistry - VIII
Session Chairs
Wednesday AM, December 01, 2010
Exhibition Hall D (Hynes)
9:00 PM - EE6.1
An Investigation of Electronic Band Gap Engineering in ZnO1-xSx Thin Films by the Technique of Spray Pyrolysis.
Hung-Chun Lai 1 , Vladimir Kuznetsov 1 , Peter Edwards 1 , Danny, S.L. Law 2
1 Inorganic Chemistry Laboratory, Department of Chemistry, University of Oxford, Oxford United Kingdom, 2 National Centre for Electron Spectroscopy and Surface Analysis, Daresbury Laboratory, Warrington United Kingdom
Show AbstractGeneration of Hydrogen by water splitting and the utilization of solar energy to conduct the splitting is a sustainable, safe, and environmentally friendly method of producing solar fuels. The ideal semiconductor material for water splitting reaction must be corrosion-resistant and absorb sunlight significantly. Metal oxide semiconductors, such as TiO2, ZnO and In2O3 fulfill one of these criteria, but the electronic band gap of these materials are all above 3.2 eV, which means that only high-energy ultraviolet radiation can act as a photocatalyst. Therefore, how to lower band gap down to the visible range is the most challenging of projects and the focus of my work. ZnO is an II-VI semiconductor and the band gap of ZnO is 3.30 eV. It shows many advantages of anti-corrosion, high carrier mobility and the aim of my project is to “engineer” the electronic band gap and crystal structure by blending sulfur elements so that band gap engineering could be facilitated in the ZnO1-xSx system. In my study, spray pyrolysis which is non-vacuum, lost cost and simple has been used for making samples. X-ray diffraction (XRD) determines the formation of ZnO1-xSx solid solution and (002) diffraction peak shifted to low angle as the evidenc of bigger size of Sulful substituting Oxygen. Hall-effect measurement and Atomic Force Microscopy (AFM) were used to understand the electronic properties and morphology. UV-Vis shows optical band gap narrowing as the increase of sulfur content. Also, this effect could be observed in Valence Band Maximun (VBM) sprctra. It suggested that sulfur supplies extra states above the edge of valence band and therefore electorns populated from these states to conduction band. As a result, the onset of VBM shifted to lower energy. The narrow of band gap is excepted to enhance the efficiency of water splitting system because it allows to absorb more visble light.
9:00 PM - EE6.10
The Effect of Dopant Phase on Optical, Electronic, and Structural Properties of Femtosecond Laser-doped Silicon.
Matthew Smith 1 , Yu-Ying Lin 2 , Meng-Ju Sher 2 , Mark Winkler 1 , Bonna Newman 1 , Joseph Sullivan 1 , Tonio Buonassisi 1 , Eric Mazur 2 , Silvija Gradecak 1
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 , Harvard University, Cambridge, Massachusetts, United States
Show AbstractIrradiation of silicon with a train of femtosecond laser pulses in the presence of chalcogens (S, Se, Te) produces ultra-highly doped silicon (~1% atomic) with near-unity absorption in the infrared (IR). Many questions remain about femtosecond-laser doping as a general platform for synthesizing ultra-highly doped materials for intermediate-band photovoltaics, and a better understanding of the relationship between process parameters and the resulting dopant distribution is essential for controllable material synthesis. We investigate the effect of dopant phase on the optical, electronic, and structural properties of femtosecond laser-doped silicon. Silicon was irradiated with femtosecond laser pulses under three synthesis conditions: with a gaseous dopant precursor (SF6), with a thin-film dopant precursor (selenium), and without a dopant precursor. We find the dopant phase strongly influences the optical, electronic, and structural properties of femtosecond laser-doped silicon. Energy dispersive x-ray spectroscopy and cross-sectional TEM show that the dopant distribution in thin-film laser-doped surfaces is confined to discontinuous polycrystalline regions. In contrast, the gas-phase doped surfaces have a continuous surface layer of doped material. Electronic measurements of current-voltage properties and the Hall coefficient indicate that thin-film doped surfaces have less favorable transport properties, likely arising from the discontinuous dopant incorporation. Raman spectroscopy revealed pressure-induced metastable phases of silicon in all samples regardless of the dopant, and selected area diffraction and convergent beam electron diffraction were used to study the spatial distribution of these metastable phases. The structure of thin-film doped surfaces cannot be explained by the current model for gaseous dopant incorporation. Implementation of femtosecond laser doping using thin-films necessitates a thorough understanding of the dopant incorporation process. This work makes significant strides toward a more sophisticated understanding of the laser doping process.
9:00 PM - EE6.11
Size-controlled Colloidal GeTe Nanocrystals with Size-tunable Ferroelectric Ordering and Nonlinear Optical Functionality.
Mark Polking 1 , Haimei Zheng 2 3 , Jeffrey Urban 4 , Delia Milliron 4 , Matt Langner 5 , Emory Chan 4 , Marissa Caldwell 6 , Simone Raoux 7 , Christian Kisielowski 3 , Joel Ager 5 , Ramamoorthy Ramesh 1 5 , Paul Alivisatos 2 5
1 Materials Science and Engineering, University of California, Berkeley, Berkeley, California, United States, 2 Department of Chemistry, University of California, Berkeley, Berkeley, California, United States, 3 National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 4 The Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 5 Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, New York, United States, 6 Department of Chemistry, Stanford University, Stanford, California, United States, 7 , IBM T. J. Watson Research Center, Yorktown Heights, New York, United States
Show AbstractColloidal chemistry has provided a simple and scalable approach to the synthesis of size-controlled nanocrystals with diverse functionalities. These successes, however, have seldom extended to the preparation of nanomaterials exhibiting spontaneous ferroelectric ordering. This lack of effective approaches to high-quality nanocrystals of ferroelectric materials has hindered elucidation of the fundamental nature and size-stability of ferroelectric ordering at nanoscale dimensions, leading to conflicting reports suggesting a transition to a toroidal state, incoherent local distortions, or a complete suppression of the polar phase. In this work, we report the first colloidal route to size-controlled nanocrystals of the simplest ferroelectric, germanium telluride (GeTe), which has received much attention due to its reversible amorphous-to-crystalline phase transition and its substantial room-temperature ferroelectric distortion. Nanocrystals with average diameters of 8, 17, 100, and 500 nm and size distributions of 10-20 percent were prepared using a divalent germanium precursor. Investigations with dark-field transmission electron microscopy (TEM) and electron diffraction suggest a transition from a monodomain to a multidomain state at sizes larger than 20 nm, and Rietveld refinements of synchrotron diffraction spectra indicate a size-dependent room-temperature ferroelectric distortion that remains stable in particles less than 5 nm in diameter. Detailed temperature-resolved synchrotron diffraction and Raman spectroscopy studies indicate a reversible, size-dependent ferroelectric phase transition at temperatures exceeding 150 °C that retains displacive character down to the smallest sizes examined. Atomic-scale studies of individual nanocrystals with aberration-corrected TEM indicate that the ferroelectric ordering retains substantial linear character, in contrast to theoretical studies suggesting the emergence of a toroidal state. These studies also reveal substantial deviations from the average structure at the unit cell scale, suggesting decreasing coherence of ferroelectric ordering. In addition, second harmonic generation measurements demonstrate nonlinear optical functionality in these nanocrystals, suggesting a pathway to nanoscale nonlinear optical components.
9:00 PM - EE6.13
Cobalt Coordination and Clustering in α-cobalt Hydroxide: Tuning Magnetic Properties with Kinetically Controlled Hydrolysis.
James Neilson 1 2 3 , Brent Melot 2 4 , Joshua Kurzman 2 5 , Daniel Shoemaker 2 4 , Ram Seshadri 2 4 5 , Daniel Morse 1 2 3
1 Biomolecular Science & Engineering, University of California Santa Barbara, Santa Barbara, California, United States, 2 Materials Research Laboratory, University of California Santa Barbara, Santa Barbara, California, United States, 3 Institute for Collaborative Biotechnologies, University of California Santa Barbara, Santa Barbara, California, United States, 4 Materials, University of California Santa Barbara, Santa Barbara, California, United States, 5 Chemistry and Biochemistry, University of California Santa Barbara, Santa Barbara, California, United States
Show AbstractStudies of biomineralization in marine sponges led to our identification of a critical role for the slow, catalytic hydrolysis of molecular precursors in the biogenesis of silica. This motivated us to study the role of kinetically controlled hydrolysis of hydrated metal ions in aqueous solutions. As a model system, we have developed a process for preparing inorganic materials involving the diffusion of a hydrolytic catalyst across an air-water interface to reproduce some aspects of the chemistry found in biomineralization, namely kinetic and vectorial control. Variation of the catalyst concentration yields an entire family of materials related to the α-Co(OH)2 structure, each with a unique composition, despite being prepared from identical mother liquors. We utilize synchrotron X-ray and time-of-flight neutron total scattering methods to locate the atomic positions, which are not aptly described by a traditional crystallographic unit cell because of inter-lamellar disorder. Our tightly coupled control of synthesis and knowledge of local and average structures of these materials gives us insight into the unusual magnetic properties of these cobalt hydroxides. The low-temperature magnetism is glassy as a result of short-range uncompensated clusters of spins which coexist within Neél-type ferrimagnetic order as determined from powder neutron diffraction. We discuss the origin of this behavior in the context of the local arrangement of metal ions and demonstrate how this structure and its associated magnetic behavior are directly determined by the precursor hydrolysis rate. By systematically varying the kinetic conditions of synthesis, we demonstrate interesting control of local structure and properties not attainable through traditional means.
9:00 PM - EE6.14
Running Before Walking – Can Pitfalls Be Avoided In Neutron Spectroscopy of Framework Materials?
Andrew Seel 1 , A. Sartbaeva 1 , A. Rammirez-Cuesta 2 , J. Mayers 2 , P. Edwards 1
1 Inorganic Chemistry Department, University of Oxford, Oxford United Kingdom, 2 ISIS Fascility, Rutherford Appleton Laboratory, Didcot United Kingdom
Show AbstractMicroporous materials, whether crystalline or amorphous, have traditionally fascinated condensed-matter chemists. We present inelastic neutron scattering and neutron compton scattering studies on two examples of mesoporous materials with guest complexes – absorbed NH3 at low concentration in zeolite A, and NaH microcrystals within amorphous silica gel. In the case of zeolites, microporosity coupled with low density and high crystallinity has led them to become some of the most utilized and archetypal materials for the encapsulation, adsorption and storage of small molecules. Amorphous silica gel can been used to intercalate important catalytic metals (such as Na or K) and subsequent reactions can yield encapsulated yet catalytically active salt species. Whatever the final goal in materials development of microporous systems, research into the fundamental physicochemical interaction between host and guest is of utmost importance. An ongoing problem in the study of framework systems containing guest species is the spectroscopic isolation of said species from their bulk host. Most studies in this area incorporate spin-chemical techniques, which, whilst structurally informative, have associated drawbacks in concentration and specific spin-state of guest species. We present an alternative approach to this problem, that of neutron spectroscopy. To date we have shown that inelastic neutron scattering (INS) can both detect and rationalise the coordination of ammonia to cationic species within zeolite-A (for distinctly different chemical systems NaA and CuA), with discussion of ammonia concentration, temperature and the role of momentum transfer on vibrational features. Despite disorder inherent at low concentrations of ammonia within zeolite-A, we demonstrate that specific vibrational regions can be defined in the INS spectra, which can be rationalised by the simple application of density functional calculations to model the partial phonon density of states, with structures pre-optimised by geometric simulation. Regions equating to translation, libration and tilting of the ammonia molecule can be assigned.We also present work detailing the application of deep-inelastic neutron scattering (DINS, also known as Neutron Compton Scattering, NCS) to the study of frameworks, with a comparison of the approaches to zeolite-guest systems and silica-gel encapsulated species, exemplified by NaH within the silica framework. This technique is rarely utilised in the more applied physical sciences, but recent advances in data refinement have enabled progressively more complex systems to be examined.
9:00 PM - EE6.16
DLC-coated Substrate for Infrared Absorption Spectroscopy in Supercritical Water.
Takuji Ube 1 , Takashi Ishiguro 1
1 Department of Materials Science and Technology, Tokyo University of Science, Noda, Chiba, Japan
Show AbstractWater is one of the most accessible, safe, inexpensive materials. In particular, use of the water at high temperature and pressure (HTP) including supercritical state has been expected to be an environmentally friendly technology as it emits no pollutants in the fields of food, drug medicine, and semiconductor manufacturing, etc. In addition, extreme environments such as an abyssopelagic hydrothermal vent have attracted much attention from geological science and biological evolution points of view. In our previous study, it was confirmed that by boiling in ultrapure water, metallic aluminum thin film on glass substrate was transformed into transparent boehmite (aluminum hydroxide) film, which showed larger optical transmittance than that of the glass substrate itself (T. Ishiguro et al, J. Appl. Phys., 106, 023524 (2009)). The film reforming of functional material could be accelerated by using water at HTP. With increasing temperature and pressure, the reactivity of water increases. Depending on conditions, severe reaction takes place in the water and the substrate itself is degraded. In addition, detection of water molecule and/or hydroxyl is important in the hydrothermal reaction. One of the useful methods to detect them is infrared absorption spectroscopy. Therefore in order to investigate hydrothermal reforming of functional films at the HTP condition, it is essential that the substrate is transparent material in a range of infrared and is stable in HTP water. In this study we have examined stability of the several kinds of substrate materials in the supercritical water. As the substrate candidates, Corning #1737 glass, fused silica, synthetic silica, water free synthetic fused silica, CaF2, ZnSe, Ge and Si were examined. In addition, Si coated with diamond like carbon (DLC) deposited by plasma CVD method was examined. Specimens were kept in the water of supercritical state (663K and 25MPa) for 2 hours using a hastelloy cell. Then, morphological change in the surface was observed by SEM. Change in the infrared transparency was measured by using FT-IR spectrometer. Almost all of specimens were degraded except the DLC-coated Si. Change in appearance of the synthetic silica and the water free synthetic fused silica was not so serious, however, the absorption corresponding to Si-OH bonding increased. Surface of Si without coating became porous, however, DLC-coated Si remained its mirror surface. As the result, DLC-coated Si is useful substrate for the IR spectroscopy in the supercritical water. The detailed results will be described in the meeting.
9:00 PM - EE6.17
Size- and Shape-controlled Synthesis of Oxide Nanoparticles by Room Temperature Vapor Diffusion Catalysis.
Krisztian Niesz 1 , Christie Reji 1 , James Neilson 1 2 , Daniel Morse 1 2
1 Institute for Collaborative Biotechnologies, University of California, Santa Barbara, Santa Barbara, California, United States, 2 Biomolecular Science & Engineering, University of California, Santa Barbara, Santa Barbara, California, United States
Show AbstractWe describe a method for the size- and shape-selective synthesis of oxide nanoparticles, specifically focusing on the formation of ceria (CeO2) nanocrystals. We describe a vapor diffusion based catalytic process that provides good control over particle formation and precise tunability of size and morphology, all achieved at room temperature and without the use of additional surface capping agents. As a consequence of the kinetically controlled base-catalyzed hydrolysis of the cerium (III) nitrate precursor molecules followed by subsequent poly-condensation, an unusual evolution of nanoparticle morphologies was observed. Detailed characterization by transmission electron microscopy (TEM), X-ray diffraction (XRD) and UV-Vis spectroscopy revealed the importance of the solution pH. As the hydroxyl ion concentration of the reaction medium increased through the progressive diffusion of ammonia catalyst vapor into the precursor solution, crystals grew from amorphous small seeds to the final ~ 10 nm particles with unusual development of well-defined crystal morphologies. Quasi-spherical particles grew to form truncated octahedra that subsequently grew with face reconstruction to yield cubic nanocrystals with the energetically least stable {100} surfaces exposed. We believe that the slow, progressive increase in hydroxyl ion concentration resulting from the controlled diffusion of ammonia into the reaction medium leads to a dynamically changing growth environment that permits us to observe the sequence of evolutionary transformations and deduce a probable mechanism. We propose a model for nanoparticle formation, suggesting that the increase in OH- concentration provides the driving force for the increased growth rate along the <111> direction, while the exposed and otherwise unstable, polar {100} surfaces are stabilized through OH- adsorption. The progressive increase in basicity also lead to internal cracking that resulted in lattice expansion of the final CeO2 particles. The predictably tunable size- and shape-selective formation of ceria nanoparticles offers potential advantages for a number of catalytic applications.
9:00 PM - EE6.18
Stabilize the Photoluminescence of PbSe QDs.
William Yu 1
1 Department of Chemistry and Biochemistry, Worcester Polytechnic Institute, Worcester, Massachusetts, United States
Show AbstractPbSe nanocrystals are useful in many fields in the near-infrared wavelength, such as telecomminucation, solar cells, bioimaging, etc. However, its application is highly limited by its instability against to air, light, and other conditions. One way to increase its stability but preserve its property is to growth a shell material on the surface. We have worked on shell growth with CdSe, ZnSe, ZnS, CdS, and found the stability can be greatly increased. We will report our synthesis work and the stability study on the PbSe nanocrystals with shell materials.
9:00 PM - EE6.19
Gas Sensing Properties of Co3O4-Doped Bismuth Oxychloride Nanowires and Nanoribbons.
Carlos Michel 1 , Alejandra Cruz-Hernandez 1 , Angel Yocupicio-Yocupicio 1
1 Department of Physics, Universidad de Guadalajara, Guadalajara, Jalisco, Mexico
Show AbstractIn recent years, the emission of carbon dioxide and other green-house gases has triggered the global climate change. With the purpose of monitoring the concentration of these gases, chemical sensors have been developed from several years. Pure and doped SnO2 has been one of the most studied materials for gas sensors; however, other inorganic oxides are promising materials for this application. Bismuth oxychloride (BiOCl)is a well known material used in the cosmetics industry, due to its extremely low toxicity. Other important applications of this material can be found in pharmaceuticals, battery cathodes, photocatalysis and photoelectrochemical devices. However, few it is known about the gas sensing properties of composites made with this material and transition metal oxides. In this work, Co3O4-doped BiOCl was synthesized by a surfactant-assisted method, using bismuth chloride, cobalt nitrate and polyvinyl pyrrolidone (PVP). Ethyl alcohol and acetic acid were used as solvents. Cobalt nitrate and PVP were dissolved in ethyl alcohol; then, this solution was added to bismuth chloride dissolved in acetic acid. The latter was stirred for 18 h at room temperature. Microwave radiation, at low power, was applied for solvent evaporation, producing a solid precursor. The thermal decomposition of the precursor at 600°C produced a two-phase material composed of Co3O4 and BiOCl; which was characterized by X-ray powder diffraction. SEM images show abundant formation of nanowires and nanoribbons. Their length was in the range of 50 to 600 μm, having a cross section size between 50 nm and 15 μm. The TEM observation of nanoribbons revealed the presence of smooth surfaces, with nanoparticles adhered to them. Dislocations may also be present. The large specific surface area of this material suggests its possible application as gas sensor.The gas sensing characterization was carried out on thick-films of the Co3O4–BiOCl composite calcined at 600°C. The technique used for deposition was screen printing, using alumina plates as substrates. Prior to the gas sensing characterization, the films were sintered at 400°C, to improve the connectivity between nanowires and nanoribbons. Alternating current (AC) measurements were done at several operation temperatures, using a LCR meter. The test gases were air and 100 ppm of CO2 (in air). The resulting |Z| vs. time graphs, recorded at 200°C and 10 kHz displayed a uniform gas response, corresponding to a p-type semiconductor material. The variation of |Z| was ~2.2 MΩ. In further tests it was observed that the increase in the operation temperature reduced the value of |Z|, which agree with the behavior of a low-pass filter. Direct current experiments were also performed in order to test the ability of the Co3O4–BiOCl composite to detect variations in the concentration of CO2. Positive results were also obtained in this case.
9:00 PM - EE6.2
Growth and Properties of Mid-infrared Nonlinear Optical Crystal LiInS2.
Shanpeng Wang 1 , Xutang Tao 1 , Chunming Dong 1 , Minhua Jiang 1
1 , Institute of crystal materials, Jinan China
Show AbstractOver the past few decades,widely tunable coherent mid-infrared laser sources in the range of 3-20 μm, specially in band 3-5 μm and band 8-14 μm of three atmospheric transparent windows, have become the research focus of infrared (IR) laser technology[1]. Frequency conversion by an infrared nonlinear optical (NLO) crystal is an effective way of producing coherent mid-infrared light. Lithium thioindate (LiInS2) is a promising candidate for optical frequency conversion. It has wide transparency range (0.35~12.5μm), high nonlinear coefficient and is phase matchable over a large wavelength range. Compared to other infrared nonlinear crystals, such as silver thiogallate (AgGaS2) [2] and zinc germanium phosphide (ZnGeP2) [3], LiInS2 displays a nearly isotropic thermal expansion behavior and a 5-times-larger thermal conductivity. Owing to its wider band gap and lower absorptions in the range of near infrared, LiInS2 crystals can be pumped by Nd: YAG laser.In this paper, we report the growth and some properties of large-sized LiInS2 crystals. The crystal with the diameter of 16 mm was grown by the modified Bridgman method. The characterizations such as XRD, high resolution X-ray diffractometor, damage threshold and refractive index of the grown crystals are also discussed.References:[1] Fossier, S.; Salaun, S.; Mangin, J.; Bidault, O.; Thenot, I.; Zondy,J. J.; Chen, W. D.; Rotermund, F.; Petrov, V.; Petrov, P.; Henningsen,J.; Yelisseyev, A.; Isaenko, L.; Lobanov, S.; Balachninaite, O.; Slekys, G.; Sirutkaitis, V. J. Opt. Soc. Am. B 2004, 21, 1981.[2]G.A.Verozubova, A.I.Gribenyukov, V.V. Korotkova, O. Semchinova, D. Uffmann, J. Crystal Growth, 2000, 213, 334. [3] D.Lee, T.Kaing, J.-J. Zondy, Appl. Phys. B, 1998, 67, 1259.
9:00 PM - EE6.20
Enhanced Photoelectrochemical Properties OfElectrodeposited Iron Oxide (α-Fe2O3) Films Using Surface Treatments.
Ryan Spray 1 2 , Kyoung-Shin Choi 1
1 Department of Chemistry, Purdue University, West Lafayette, Indiana, United States, 2 Mechanical Engineering and Material Science Practice, Exponent Failure Analysis Associates, Natick, Massachusetts, United States
Show AbstractIron Oxide (α-Fe2O3) is an n-type semiconductor with a band gap that allows forthe absorption of ~40 % of the incident solar spectrum, and is stable in most aqueouselectrolytes (pH > 3). In addition to being environmentally benign, very abundant, andinexpensive, iron oxide photoelectrodes can be processed by a wide variety of syntheticmethods (i.e. spray pyrolysis, CVD, electrodeposition). Major challenges facing the use of iron oxide photoelectrodes for water-splitting applications are poor charge transport properties and slow interfacial kinetics for water oxidation reactions.This poster will present a simple and general method to modify the compositions of nanostructured α-Fe2O3 electrodes in order to improve the photoelectrochemical properties for water splitting. In particular, the effect of Al and Sn ions incorporated into the surface of α-Fe2O3 nanoparticles are investigated in detail in this study. This treatment does not alter the nanostructured morphology of the films, as Scanning Electron Microscopy (SEM) images will show. Energy-Dispersive X-ray Spectroscopy (SEM/EDS) and X-ray Photoelectron Spectroscopy (XPS) data presented will show the distribution and the content of dopant ions and/or solid-solutions, and a combination of UV-vis, photocurrent, incident photon-to-current (IPCE), and conductivity studies will be presented to show increased charge-transport and photoelectrochemical water oxidation properties. When used in concert, the Al- and Sn-treatments produce the greatest improvement. The method described in this study is a post-deposition treatment and, therefore, can be combined with any deposition technique to further improve properties of nanostructured α-Fe2O3 electrodes via composition tuning.
9:00 PM - EE6.21
Two-step Sintering Process for Lutetium Oxide Transparent Ceramics.
Xiaomei Guo 1 , Kewen Li 1 , Yanyun Wang 1 , Yingyin Zou 1 , Hua Jiang 1
1 , Boston Applied Technologies, Inc., Woburn, Massachusetts, United States
Show AbstractDuring a two-step sintering practice, important factors such as final grain sizes and residual pore status can be controlled through adjusting the first and second step sintering temperatures and durations. Moreover, the sintering temperatures (both the first and the second step) can be several hundred degrees lower than those in a traditional sintering process to obtain fully dense ceramics. Therefore, it is a potentially cost-effective preparation procedure for ceramics with fine grains.In this work, we successfully demonstrated the synthesis of aggregate-free sesquioxide nanometer-sized powders with a narrow size distribution through a modified chemical co-precipitation process. Subsequently, ytterbium-doped Lu2O3 ceramics of near full density were obtained through a two-step sintering process.
9:00 PM - EE6.22
Computational Exploration of Novel Photoreactions Involving Halogenated Ruthenium Polypyridyl Complexes.
Paul Vallett 1 , Niels Damrauer 1
1 Chemistry, University of Colorado at Boulder, Boulder, Colorado, United States
Show AbstractA density functional theory study is undertaken to explore new processes to extend the lifetime of excited-state ruthenium polypyridyl complexes for use in converting solar energy to electrochemical work. This study focuses on lowering the ΔErxn of the heterogeneous halogen-carbon bond scission after absorption of a photon and formation of the triplet metal to ligand charge transfer (3MLCT) state as seen in the following reaction: [RuII(A)n(L-X)]2+ + hν --> [RuIII(A)n(L-X●)-]2+ --> [RuIII(A)n(L●)]3+ + X- (L = polypyridine ligand, X = Cl, Br, I, A = Ancillary ligand). The reaction effectively prevents energy wasting charge recombination and produces a high energy carbon radical along with an oxidizing center, both of which could be useful in artificial photosynthetic processes. A thermodynamic cycle is employed which uses the following steps to determine ΔErxn: halogen bond dissociation energy (BDE), oxidation of the metal complex (E3+/2+), electron affinity of the halogen atom (EA), and energy stored in the 3MLCT state. An examination of the B3LYP, B3P86, B3PW91, and PBE0 functionals performance on the steps listed above, along with a comparison to geometric parameters of the ground state of ruthenium polypyridyl complexes was undertaken to determine the most appropriate functional. PBE0 with an SDD electron core potential (ECP) describing the Ru and halogen performed most consistently while the popular B3LYP with LANL2DZ ECP did not. Calculation of the thermodynamic cycle for model halogenated [Ru(bpy)2(bpy-X)]2+ (bpy = 2,2’-bipyridine, bpy-X = 4-X-2,2’-bipyridine) complexes revealed that E3+/2+ was the major step causing the reaction to be endothermic, with a ΔErxn = 0.7 eV. A decrease in E3+/2+ was achieved through methylation of the ancillary polypyridines ([Ru(tmb)2(bpy-X)]2+, tmb = 4,5,4’,5’-tetramethylbipyridine) and through use of amines as ancillary ligands ([Ru(NH3)4(bpy-X)]2+). To counter-act the concurrent reduction in 3MLCT energy the halogenated polypyridyl was methylated as well ([Ru(NH3)4(tmb-X)]2+, tmb = 4-X-5,4’,5’-trimethylbipyridine). Additional reduction in ΔErxn was obtained through steric effects arising from attachment of the halogen at the 6 or 3 position of a bipyridine ligand which significantly lowered the BDE. Together these effects lead towards an achievable ΔErxn of 0.086 eV (for [Ru(NH3)4(tmb-3-Br)]2+, tmb-3-Br = 3-bromo-4,5,4’,5’-tetramethylbipyridine).
9:00 PM - EE6.23
Synthesis of NaTaN2 by Ammonothermal Method.
Kazuhisa Kishida 1 , Jinwang Li 2 , Masahiro Yoshimura 2 , Tomoaki Watanabe 1
1 Applied Chemistry, Meiji university, Kawasaki, Kanagawa, Japan, 2 Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama, Kanagawa, Japan
Show AbstractTernary nitrides are relatively unexplored compounds in the field of material science. There have been many studies on the synthesis of single nitride, especially for the mechanical application materials, such as AlN, TiN, Si3N4 and so on. However, to our knowledge, very few researches which related complex nitrides have been reported. In generally, those complex nitrides were prepared by heating with two kinds of binary nitride at very high temperature under N2 atmosphere, and using precursor such as metal amide. The NaTaN2 is known as complex alkali metal nitride, which was synthesized by heating sodium amide NaNH2 and metal compound (Ta2O5, TaCl5, etc.) under ammonia pressure at several handred MPa.[1] In the present study, we have succeeded to synthesize a complex nitride, NaTaN2, via reaction of a metal Ta and Na in supercritical ammonia fluid (ammonothermal condition). Under the ammonothermal condition, NaTaN2 fine crystal was formed at ≥ 673 K and this reaction was comparatively low temperature process than typical solid state reaction (around 2000 K). The color of obtained product was yellow. By using X-ray diffraction, those phase were idenified as NaTaN2, without any impurities. The band gap of the NaTaN2 powder was estimated to be 2.2 eV from its UV-Vis diffuse reflectance spectrum. The particle size of the product was estimated to be 20–500 nm. [1] H. Jacobs and E. Von Pinkowski, J. Less-Common Met., 146, 147–160 (1989).
9:00 PM - EE6.24
Effects of Dissolved Cations on Glass Polishing Rate of Cerium Oxide Abrasives.
Seiichi Suda 1 , Koichi Kawahara 1 , Kumiko Kinoshita 1
1 , Japan Fine Ceramics Center, Nagoya Japan
Show AbstractCerium oxides are indispensable for polishing of glasses and precisely polished glasses are used as various substrates such as HDDs and flat display panels. Cerium oxides can be actually polished glasses at a high rate and the high rate is contributed by chemical reaction between cerium oxide and glass as well as mechanical polishing. However, chemical mechanical polishing (CMP) mechanism of cerium oxides is still vague. It is not known exactly why cerium oxides show exceptional polishing properties. Polishing properties are much affected by particles sizes and surface roughness as well as compositions of abrasive and it is generally difficult to separate effects of particle morphologies and abrasive compositions on glass polishing. We then prepared various cerium oxide abrasives with a homogeneous particles size. Spray pyrolysis method led to various La doped cerium oxide powder with the particles diameter of 0.6-0.8 μm. The obtained cerium oxide particles were dispersed with water and the aluminosilicate glasses were polished with slurry with the particles. The slurry containing cerium oxide powder and lanthanum oxide powder did not improve the rate, but the polishing rate was much increased with increasing La concentration dissolved in cerium oxide. Oxygen defects derived from the dissolution of lanthanum would affect the polishing rate. CMP occurs at the interface between glass and surface of abrasives. Oxygen defect concentrations on the surface of cerium oxide abrasives would much affect the polishing rate.
9:00 PM - EE6.25
Low Temperature Phase Diagram of NH3BH3.
Bertil Sundqvist 1 , Ove Andersson 1 , Issam Quwar 1 , Alexandr Talyzin 1
1 , Umea University, Umea Sweden
Show AbstractAmmonia borane, NH3BH3, contains almost 19 weight % hydrogen which can be released by heating to relatively low temperatures, 80 – 500°C. It is thus considered a potential solid-state hydrogen storage material. The material is also interesting from a basic scientific viewpoint: the intermolecular interaction is very strong, due to an unconventional dihydrogen bond[1], as shown by the difference between the solid NH3BH3 and the gas ethane, C2H6, which has a very similar molecular structures. The structure of solid NH3BH3 has recently been studied under pressure by several groups, in particular by Filinchuk et al.[2]. In the low pressure range, three structural phases are known. At atmospheric pressure a tetragonal I4mm phase is found at 293 K and an orthorhombic Pmn21 phase below 220 K, while application of pressure at 293 K leads to a transition near 1.2 GPa into another orthorhombic Cmc21 phase. In the I4mm phase the molecular axes are parallel with the c axis, but in the orthorhombic phases the molecular axes are inclined relative to the lattice axes by a pressure-dependent angle. The angle is small (about 20-25°) for the low-T phase but much larger (70-80°) for the high-p phase. The existence of a fourth low-temperature phase at high pressure is predicted by Filinchuk et al.[2] from a thermodynamic model.We have studied the phase diagram of NH3BH3 at 200-300 K under pressures up to 1.4 GPa by thermal conductivity measurements. Raman measurements have also been carried out, over somewhat wider ranges. As in earlier studies[3] both methods clearly show the first-order transformations between the I4mm structure and the orthorhombic phases. Isobaric and isothermal data show a continuous phase boundary stretching between the I4mm-Pmn21 transformation at zero pressure and the room-temperature I4mm-Cmc21 transition, indicating a continuous transformation between the two orthorhombic phases. Over most of the temperature-pressure range investigated the results are reversible with no trace of further phase transitions. However, in a small pressure interval, heating near the I4mm-Pmn21/Cmc21 phase boundary resulted in the observation of a strongly metastable material with thermal and vibrational properties different from those of the three parent phases discussed above. This new material might either be related to the fourth structural phase predicted by Filinchuk et al., or be an intermediate structure produced during the transition between the two orthorhombic phases.[1] R. H. Crabtree, P. E. M. Siegbahn, O. Eisenstein, A.L. Rheingold, T. F. Koetzle, Acc. Chem. Res. 1996, 29, 348.[2] Y. Filinchuk, A. H. Nevidomskyy, D. Chernyshov, V. Dmitriev, Phys. Rev. B 2009, 79, 214111.[3] B. Sundqvist, O. Andersson and A. V. Talyzin, J. Phys.: Cond. Matter 2007, 19, 425201.
9:00 PM - EE6.27
Magnetic Ordering in Rare-earth Cobalt Phosphides and Arsenides La1-xNdxCo2Pn2 (Pn = P, As).
Corey Thompson 1 , Kirill Kovnir 1 , Mitchell Herring 1 , Michael Shatruk 1
1 Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida, United States
Show AbstractRare earth-cobalt pnictides that belong to the ThCr2Si2 structure type are interesting not only in the context of the recent discovery of high-Tc superconductors based on this structure, but also in their own right as fascinating magnetic materials. They contain two magnetic sublattices which can lead to the existence of multiple magnetically ordered phases in the same material. Moreover, LaCo2P2 and the other members of the RCo2P2 series (R = Ce, Pr, Nd, Sm) exhibit drastically different magnetic properties. Recently, we have shown that quaternary rare-earth cobalt phosphides La1-xPrxCo2P2 exhibit rich magnetic behavior which is sensitive to the small variations of both crystal and electronic structures. In an effort to understand the role of the rare-earth element in defining the magnetic properties of these phases, we have prepared quasi-ternary phases La1-xNdxCo2P2 which also exhibit interesting magnetic properties, albeit somewhat different from those of the Pr-substituted phases. Trying to extend these studies to rare-earth cobalt arsenides, we have performed a number of experiments to repeat the only reported preparation of RCo2As2 but have not been able to obtain phase-pure samples. Therefore, alternative synthetic methods were probed, which resulted in successful preparation of phase-pure RCo2As2. Magnetic properties of these phases will also be presented.
9:00 PM - EE6.28
Temperature Dependent Structural and Dielectric Investigations on PbZr0.5Ti0.5O3 Solid Solution at Morphotropic Phase Boundary.
Geetika Srivastava 1 , Ankur Goswami 1 , Arun Umarji 1
1 Materials Research Centre, Indian Institute of Science, Bangalore, Karnataka, India
Show AbstractPbZr1-xTixO3, (PZT) is one of the most important widely investigated ferroelectric compositions due to their remarkable dielectric and piezoelectric properties which make them suitable candidate for devices as piezoelectric sensors and actuators. These materials exhibit optimum dielectric, and piezoelectric properties at ‘Morphotropic Phase Boundary (MPB)’. A high resolution diffraction study was done on sample with x = 0.5 composition which shows a signature of MPB. The temperature dependent structural study has also been done. The dielectric measurements have also been carried out in order to confirm the phase transition in the system as observed through the X-ray diffraction and will be presented. The purpose of the investigation is to determine the phase fraction of tetragonal and monoclinic phases in the coexistence region and to study the phase transformation of PZT. This information may help in basic understanding of the material properties exhibited by the system in the coexistence region.Key words : Morphotropic phase boundary (MPB), High resolution diffraction, monoclinic, tetragonal and rhombohedral phasesReferences[1] A. Safari,and E. K. Akdogan, Piezoelectric and Acoustic Materials for Transducers Applications (2008), Springer. [2] Geetika, A.M.Umarji, Mat Sci & Engg. B 167(2010), 171[3] M R. Soares, A. M. R. Senos and P. Q. Mantras, J. Eur. Ceram. Soc. 19 (1999), 1865.
9:00 PM - EE6.29
Growth and Characterization of Shape-controlled Single Crystals by a micro-pulling-down Method.
Yuui Yokota 1 , Masato Sato 1 2 , Valery Chani 1 , Kazushige Tota 2 , Ko Onodera 2 , Takayuki Yanagida 1 , Akira Yoshikawa 1
1 , Tohoku University, Sendai Japan, 2 , TDK Corporation, Nikaho Japan
Show AbstractVarious functional bulk single crystals grown by Czochralski(Cz), Bridgman-Stockbarger (BS) and Floating Zone (FZ) methods have been applied in a wide field such as optical equipments, radiation medicine, single crystal substrate and so on. Relatively large bulk crystals with several centimeters in diameter can be obtained by these methods in several days or weeks growth period. In many industrial and research fields, functional crystals must be shaped to fit on each application and evaluation by cutting and polishing with the greatest care to prevent some damages to the crystals. Therefore the processing cost of bulk crystals strongly affects final prices of various products with single crystal.In contrast, a micro-pulling-down (μ-PD) method can grow relatively small crystals with a couple of millimeters in diameter at a several times faster speed than that of Cz, BS and FZ methods. In addition, the μ-PD method can control the shape of grown crystal by a crucible with a specific configuration. On these backgrounds, we have developed the technique of figure control on functional single crystals grown by μ-PD method and investigated the crystallinity and physical properties of shape-controlled crystals. Shape-controlled sapphire and CaF2 single crystals were grown by μ-PD method. Al2O3 ( > 4N purity) and CaF2 ( > 3N purity ) powders were entered molybdenum and carbon crucibles with a specific configuration, respectively and crucibles were heated by high-frequency induction coil. Sapphire crystals were grown under N2 flow and CaF2 crystals were grown in high purity Ar/CF4 mixed gas after baking process for elimination of moisture from the surface of starting materials and equipment. Chemical compositions and crystallinity of grown crystals were investigated by SEM/EDX, powder X-ray diffraction and X-ray rocking curve. Optical properties of grown crystals were evaluated by transmittance and photoluminescence measurements.We grew multiple square columns, circular tube and square tube of sapphire and circular tube and square tube of CaF2 crystals by μ-PD method. The molybdenum crucibles with die which had multiple squares, circular tube and square tube shapes for shaped-controlled sapphire crystal growth were used due to the good wetting behavior between sapphire melt to molybdenum. In contrast, the carbon crucibles which had each shape hole of circular tube and square tube on the bottom were used for CaF2 crystals growth due to the bad wetting behavior between CaF2 melt and carbon. All grown crystals have high crystallinity and transparency comparable to crystals grown by Cz method. No cracks and visible inclusions were observed in the crystals. The crystallinity and physical properties at each position of shaped-controlled crystals will be reported.
9:00 PM - EE6.30
Synthesis and Photocatalytic Activity of Crystalline Mesoporous C and N- co-doped TiO2 Nanophotocatalyst.
Yasuro Ikuma 1 , Srinivasan Anandan 2 , Hiroaki Fukushima 1 , Koichi Niwa 1
1 Applied Chemistry, Kanagawa Inst. of Tech., Atsugi, Kanagawa, Japan, 2 , AIST, Tsukuba, Ibaraki, Japan
Show AbstractThere are several works which reported the formation of mesoporous N-doped TiO2. Chi et al. synthesized mesoporus N-doped TiO2 by a template free solvothermal method and concluded that mesoporous N-doped TiO2 showed enhanced visible light activity compared to undoped TiO2. Choi et al. and Ren et al. reported the synthesis of mesoporous C-doped TiO2 and mesoporous N-doped TiO2 and found significantly higher photocatalytic activity for these materials. However, most of these previous studies are limited to the mesoporous materials with low crystallinity.In this paper, we demonstrate a synthesis route for the preparation of highly crystalline mesoporous carbon/nitrogen, co-doped TiO2. The synthesis of highly crystalline novel mesoporous TiO2 has been performed using KIT-6 as the template, and titanium tetra-isopropoxide as TiO2 source. The obtained material has been characterized by various techniques. XRD and TEM analysis revealed that the material possess highly crystalline 3D structure with continuous network of mesoporous channels as well as structure corresponds to TiO2. UV-DRS analysis indicated that light absorption shifted to the visible-light region. It has been found that the material is highly crystalline and possesses high surface area, pore volume and uniform pore size distribution. The mesoporous TiO2 has been tested with the adsorption and degradation of rhodamine B. Although regular TiO2 powder did not show any adsorption of rhodamine B, most of mesoporous C and N- co-doped TiO2 show very good adsorption of rhodamine B. The degradation of rhodamine B was very straight forward when regular TiO2 was used. However, the degradation was accomplished by decomposition of the original molecules when mesoporous C and N- co-doped TiO2 was used. Owing to its textural characteristics, it could be useful for various applications, such as photocatalysis, fuel cells, molecules adsorption and nanotechnology.
9:00 PM - EE6.31
n-Alkylamine-assisted Preparation of High Surface Area Vanadyl Phosphate/Tetraethylortosilicate Nanocomposite.
Herenilton Oliveira 1 , Joao Paulo Ferreira 1 , Elaine Zampronio 1
1 Chemistry, Sao Paulo University/FFCLRP, Ribeirão Preto, São Paulo, Brazil
Show AbstractVanadium-phosphorous oxide heterogeneous catalysts play an important hole in several organic syntheses such as oxidation of propane to acetic acid and oxidation of butane to maleic anhydride. Despite their widespread technological uses, there has been an increasing interest in the synthesis of high surface area catalysts. In this context, we have developed a novel nanocomposite material, vanadyl phosphate/tetraethylorthosilicate (VPO/TEOS), comprised of silicate chains interleaved with the layers of VPO, prepared by using an n-alkylamine such as octylamine as the structure directing agent. The nanocomposites were synthesized by reacting amine-intercalated vanadyl phosphate with tetraethylorthosilicate using soft chemistry approach. The characterization of this material using specific surface area using BET method, SEM, FTIR spectroscopy, powder XRD, and thermal analysis shows the exfoliation of the layered vanadyl phosphate as well as the reorganization of this exfoliated solid into a mesostructure lamellar phase having the same V-P-O connectivity as in the original matrix. In addition, TEOS into the vanadyl phosphate has been achieved by expanding the lamellar structure with n-alkylamine (Δd=13Å with n-octyl). Besides, XRD patterns suggest that the TEOS chains are at least partially aligned in the basal plane. The specific surface area increased dramatically, from 1.9 m2g-1 for vanadyl phosphate matrix to 187 m2g-1 for VPO/TEOS, and the isotherm curves present characteristic hysteresis of mesoporous materials. Upon thermal treatment up to 500 oC, the surface area increased to 837 m2g-1. The results of this study show that the methodology used here leads to material with high surface area suitable for catalytic purposes, when compared with other related systems. In addition, the procedure adopted is simple and the materials were obtained under soft conditions.Acknowledgement: FAPESP, CNPq and CAPES.
9:00 PM - EE6.32
Catalytic Properties of a Novel Ternary Hybrid Material Based on Cetyltrimethylammonium Bromide and n-hexadecylamine into WO3.H2O
Herenilton Oliveira 1 , Aline Bolsoni 1 , Joicy dos Santos 1 , Marilda Assis 1
1 Chemistry, Sao Paulo University/FFCLRP, Ribeirão Preto, São Paulo, Brazil
Show AbstractTungsten -based catalysts have been widely used in metathesis and isomerization of alkenes, oxidation of unsaturated compounds, and hydrocracking of heavy fractions in the petroleum chemistry, for example. In order to achieve satisfactory results, several synthetic approaches have been used to obtain catalysts, in which many of them focus the preparation of mesoporous and nanostrutured oxides or their impregnation on siliceous and nonsiliceous mesostructured materials. Herein, it is reported the synthesis of a ternary hybrid composite via the intercalation of cetyltrimethylammonium bromide (CTAB) and n-hexadecylamine (HDA) in the interlayer space of WO3 xerogel (WO3/CTAB/HAD). In order to investigate the potencial catalytic activities of ternary hybrid WO3/CTAB/HDA, we tested this material as catalyst on the direct epoxidation of alkenes because the importance of epoxides as intermediates in organic synthesis of fine chemicals of pharmaceuticals. Therefore, the catalytic properties of the resulted hybrid material were investigated for catalytic oxidation of cyclooctene, styrene, and cyclohexane employing H2O2, tert-butyl hydroperoxide (t-BOOH), and m-chlorperbenzoic acid as oxygen transfer agents. Scanning electron microscopy, powder X-ray diffraction, infrared spectroscopy, thermogravimetric analysis, UV-Vis absorption and electron spin resonance (ESR) techniques were used to characterize this new hybrid material. The oxidation reactions were performed under reflux, using acetonitrile as solvent, and heated 25oC and 60 oC, under magnetic stirring. 3.0mg of the catalyst was added to the hydrocarbon (0.5mmol), and tert-butyl hydroperoxide (t-BOOH), m-chlorperbenzoic acid (m-CPBA) and Hydrogen peroxide (H2O2) were used as oxidants. The catalyst: oxidant: substrate molar ratio was 1:1,000:20,000. On oxidation of cyclooctene, best yields were achieved for the use of m-CPBA as oxidant, lead into 88% conversion at 25 oC. The styrene oxidation leads to benzaldehyde. The styrene oxidation leads to styrene epoxide as the major product (epoxide yield = 26%), but formation of benzaldehyde (yield = 2%) also occurs when H2O2 was used as the electron transfer agent. For oxidation of cyclohexane, best results were achieved by the use of t-BOOH as oxidant, leading to 100 % conversion, at both 25 and 60 oC temperatures, selectively to cyclohexanone. Reaction with m-CPBA is highly selected, leading exclusively to cyclohexanol, and the results of H2O2 leads into 26% of conversion. From general point of view, these results are comparable to those obtained with related systems suggesting its potentiality as catalyst for epoxidation reactions.Acknowledgement: FAPESP, CNPq and CAPES.
9:00 PM - EE6.33
Crystal Field Approach to Modeling of Local Site Positions of Fe Ions in Y3Fe5 O12 Garnett: Experiment and Theory.
Kazimierz Plucinski 1 , I. Kityk 2 , M. Brik 3
1 Electronics Department, Military University of Technology, Warsaw Poland, 2 Electrical Engineering Department, Czestochowa University of Technology, Czestochowa Poland, 3 Institute of Physics, University of Tartu, Tartu Estonia
Show AbstractIn the present work we would like to report on the results of experimental and theoretical crystal field research into spectroscopic properties of the Y3Fe5O12 with respect to the local site positions of the particular iron ions. There are two positions for Fe3+ ions: tetrahedral and octahedral. For both available positions we have performed calculations of the Fe3+ energy levels using exchange charge model of crystal field. The experimental spectra were obtained from the UV reflection spectroscopy. The reflection spectrum was measured by vaccum monochormator Seya Numioka with spectral resolution 4 nm, using synchrotron source beam. Generally a sufficiently good agreement between the theoretically predicted and the experimentally determined energy positions was achieved. As a result of the performed simulations we have found that the spectral positions of the 4T2(4G) and 4E(4G) terms with different local site positions show the different broadening. The broadening are caused by electron-phonon interactions and interactions between the spin-polarized states and the ligand complexes. The directions of the shifts are different depending on the local positions of the Fe ions. Such differences may be used as sensitive indicator of the non-stoichiometry in the grown Y3Fe5O12 single crystals. This is particularly important for the single crystalline samples where we have a superposition of the crystalline and magnetic ordering (spin-polarized ordering). So appropriately changing the technological processes and knowing the spectral shifts on the ground of the proposed modeling for these changes one can evaluate the direction of the technological process in order to obtain desired results.
9:00 PM - EE6.34
Novel Sol-gel Methodology to Produce LaCoO3 Compound by Acrylamide Polymerization Assisted by γ-irradiation.
Giovanni Carabali 1 3 , Elizabeth Chavira 2 , Jose Jimenez-Mier 3 , Emilio Bucio 3 , Lazaro Huertas 2
1 Posgrado en Ciencias Químicas, National Autonomous University of Mexico, Mexico , Mexico D.F, Mexico, 3 Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, Mexico, D.F Mexico, 2 Instituto de Investigaciones en Materiales, National Autonomous University of Mexico, Mexico , Mexico D.F, Mexico
Show AbstractPure and doped lanthanum cobalt perovskite have potential applications as catalyst [1]. Meadowcraft [2] suggested that LaCoO3 could be used as a good solid oxide fuel cell (SOFC) material. For its applications, this material has been synthesized by different routes. New routes such as wet-chemical methods (WCM) offer interesting results [3]. These WCM are based on formation of a polymeric gel with cations chelated inside in a homogeneous manner.In this paper we have combined the concepts of polymer technology and sol–gel synthesis to prepare nanomaterials, which yield an innovative and general route for fabricating LaCoO3 policrystals. This novel sol-gel method of acrylamide polymerization assisted by γ-irradiation (γ-SGAP) show good results and improvements could be done to produce materials with better properties.In this new method, the acryl-amide monomer was polymerized using incident gamma-radiation on aqueous medium with presence of respective metals ions La3+ and Co3+. All dissolutions were put in glasses ampoules, which were degassed by repeated freeze–thaw cycles and sealed with presence of argon to remove air. The polymerization processes was carry out inside of a Gamma-beam 651 PT, MDS Nordion with a source of Cobalt-60.After γ-radiation processes we obtained a compact hidrogel, which was dried in a microwave oven operating at 600W under Ar flux. This dry-gel was grinded in an agate mortar, and the policrystals were heated at 200 °C during 12 h. Next we increased the temperature in 100 °C steps up to 500 °C. In this stage important organic material are removed and nano-crystals are grown. In order to remove all organic impurities, additional heating process on dry-gel was carry out in air at temperatures ranging from 500 to 800 °C. The formation of new phases of LaCoO3 compound upon calcinations was investigated using X-ray diffraction, thermal-gravimetric analysis and Fourier-transform infrared spectroscopy. The results revealed the formation of a single-phase having the Perovskite structure at temperatures as low as 500 °C. The particles obtained are spherical and the grain sizes are in the range 20 – 90 nm.To comparative effects, LaCoO3 also was prepared by solid state reaction (SSR) and detailed XPS spectra were recorded at O 1s, La 3d, La 4d and Co 2p regions of compound synthesized by both methods. These XPS spectra are in agreement to those reported in previous studies [4]. Deconvolution analysis of O 1s spectra show photolines at 529.1 eV and 531.2 eV that must be assigned to lattice oxygen and adsorbed oxygen species respectively [5], this analysis evidence some differences in superficial composition of compounds obtained by γ-SGAP and SSR. [1] C. H. Kim et al., Science 327 (2010) 1624. [2] D. B. Meadowcraft, Nature 226 (1970) 847.[3] Y. Song. J sol-gel Technol 44 (2007) 139-144. [4] M. M. Natile et al., Appl. Catal.,B: Environ. 72 (2007) 351. [5] M. Imamura et al., J. Phys. Chem. B, 104 (2000) 7348-7353.
9:00 PM - EE6.35
Electric-field Induced Alignment of Modified Na-fluorohectorite Clay Particles.
Zbigniew Rozynek 1 , Baoxiang Wang 1 , Kenneth Dahl Knudsen 2 , Jon Otto Fossum 1
1 Physics, NTNU, Trondheim Norway, 2 Physics, IFE, Kjeller Norway
Show AbstractThe electric field induced alignment of organically modified sodium-fluorohectorite (Na-Fh) clay particles suspended in silicone oil was studied by means of synchrotron wide angle X-ray scattering (WAXS). This research focuses on the comparison between the anisotropic arrangement of organically modified clay particles and their previously studied non-modified counterparts. Na-Fh particles suspended in oil undergo a fast and extended structuring when subjected to an electric field. As a coarse approximation, the Na-Fh clay platelets forming the chain can be represented as disk-shaped aggregates, whose orientation is defined by a unit normal vector. Thus, the anisotropic arrangement of the system can be described by an orientation distribution that is a function of the normal vectors for all aggregates. The classical Maier-Saupe function was used for the orientation distribution, since it was found to be suited to our data, as discussed previously by Méheust, et al. The WAXS data showed that the degree of anisotropy was higher for the system with organically modified Na-Fh particles (S=0.71) than for unmodified clay particles (S=0.63). This can be explained by fact that the modified clay particles do not form large aggregates as it is the case with unmodified particles, leading to a better organization of the constituents of this electrorheological fluid.
9:00 PM - EE6.37
Novel Zinc Oxide Thin Film Morphologies by Thermal Decomposition of Zinc Acetylacetonate.
Hector Garces 1 , Anais Espinal 1 , Luis Garces 3 , Steven Suib 2 1
1 Institute of Materials Science, University of Connecticut, Storrs, Connecticut, United States, 3 Laboratorio de Catalysis Industrial, Instituto de Química, Universidad de Antioquia, Medellin Colombia, 2 Department of Chemistry, University of Connecticut, Storrs, Connecticut, United States
Show AbstractIn this work, we reported the thin film formation of ZnO with novel morphologies on glass, tin oxide coated glass (SnOx), and indium titanium oxide (ITO) coated glass from the decomposition of zinc acetylacetonate (ZnAcac) under mild conditions in a one step method. The films are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Quaternary ammonium salts were used to modify the growth behavior of the deposited zinc oxide. Cloth like, hexagonal nanorod and hexagonal end tip-nanorods morphologies are obtained over the bare glass depending of the ratio of tetrabutylammonium bromide (TBABr) used. Novel coral like morphologies are obtained over ITO coated glass with and without the use of growth modifiers with different film dense and smoothness. Deposition over SnOx coated glass produces a similar result depending of the deposition temperature. Low temperature deposition on bare glass with tetramethylammonium hydroxide (TMAH) produces films with football and sword-kind morphologies. Growth behavior, crystallite size and film thickness are evaluated. The influence of the synthesis conditions in the morphologies will be discussed.
9:00 PM - EE6.38
Oxygen Defect in PbTiO3 Thin Films Probed by Resonant Raman Scattering.
Ken Nishida 1 , Minoru Osada 2 , Joe Sakai 3 , Nobuaki Ito 4 , Hironari Takeuchi 5 , Takashi Katoda 5 , Rikyu Ikariyama 6 , Takafumi Kamo 6 , Takashi Fujisawa 6 , Hiroshi Funakubo 6 , Takashi Yamamoto 1
1 Department of Communications Engineering, National Defense Academy, Yokosuka Japan, 2 International Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba Japan, 3 Laboratoire LEMA, Universite Francois Rabelais, Tours France, 4 Center for Nano Materials and Technology, Japan Advanced Institute of Science and Technology, Nomi Japan, 5 Department of Electronic and Photonic Engineering, Kochi University of Technology, Kami Japan, 6 Department of Innovative and Engineered Materials, Tokyo Institute of Technology, Yokohama Japan
Show AbstractPb-based ferroelectric materials are one of the most successful materials to apply the electric devices such as infrared radiation sensor, microactuator and nonvolatile memory because they have excellent pyroelectric, piezoelectric and ferroelectric properties. However, since Pb and oxygen ion has high vapor pressure, Pb and/or oxygen vacancy easily occurs during crystal growth or heat treatment in device processing. Especially, it has been recognized that oxygen vacancy is inevitable defect in oxides. However, it is quite difficult to detect oxygen vacancy in slight amount of materials such as thin films. Raman spectroscopy is very sensitive to changes in the local symmetry of crystal structures including oxygen vacancy. In addition, Raman spectroscopy has advantages for structural evaluation: it is a noncontact and nondestructive method and has a relatively high spatial resolution. In this work, resonant Raman spectroscopy was applied to evaluate oxygen vacancy in PbTiO3 thin films.The PbTiO3 thin films were grown on (100)MgO substrates by metal organic chemical vapor phase deposition (MOCVD). The film thickness was 300 ~ 400 nm. The PbTiO33 thin films were heat-treated at 600 ~ 800 °C for 2 hours under the hydrogen atmosphere in order to generate various density of oxygen vacancies in PbTiO3 thin films. Raman spectra were measured using an Ar+/Kr+/ mixed gas laser (~5 mW) as an excitation that is able to change the emission wavelength from 488.0 to 568.2 nm. The laser probe beam was focused to a 1-μm-diameter spot on the sample surface. The backward scattering light was collected and dispersed by a subtractive triple spectrometer (Horiba-Jobin Yvon T64000R). The measurement time was fixed at 60 seconds. The Raman spectra indicate a typical tetragonal PbTiO3 without any secondly phase. The additional mode that was related to oxygen vacancy was observed in Raman spectrum of PbTiO3 thin films that was heat-treated in hydrogen atmosphere at the resonant Raman measurement condition. The peak intensity of this mode was enhanced with increasing the heat treatment temperature, suggesting the increase of oxygen vacancy. The intensity of additional mode scales with the oxygen vacancy content in the films that was evaluated using a non-Rutherford elastic resonance scattering technique. This relationship is very useful guideline to determine the content of oxygen ions in PbTiO3 thin film. These results indicate that resonant Raman spectroscopy is a versatile and useful tool for evaluating oxygen vacancy.
9:00 PM - EE6.39
Supercritical Fluid Deposition, Characterization, andPhotoluminescence Study of PbS Quantum Dots.
Joanna Wang 1 2 , Bruno Ullrich 1 3 , John Boeckl 1 , Gail Brown 1 , Chien Wai 2
1 , Air Force Research Lab, Materials and Manufacturing Directorate, WPAFB, Dayton, Ohio, United States, 2 Department of Chemistry, University of Idaho, Moscow, Idaho, United States, 3 Department of Physics & Astronomy, Bowling Green State University, Bowling Green, Ohio, United States
Show Abstract Lead sulfide (PbS) nanoparticles can be deposited on carbon coated copper grid and GaAs wafer using supercritical fluid carbon dioxide (Sc-CO2) as a solvent. TEM images show that PbS nanoparticles form uniform 2D or 3D arrays via Sc-CO2 deposition, whereas solution deposition usually displays ring like non-uniform PbS nanostructures. In addition, SEM images show that the PbS nanoparticles can be deposited in nanoscale pores by Sc-CO2 that cannot be achieved by traditional solvent deposition method. A comparison of the optical properties the PbS nanoparticles deposited by these two processes was made using photoluminescence (PL) spectroscopy. PbS nanoparticles were deposited on p-type GaAs substrates by both processes. The samples fabricated by the Sc-CO2 deposition process had three times the PL intensity than the solution deposited sample, which is attributed to the more uniform areal coverage. A 30 meV blue shift in the PbS related emission peak was also noted for the solution deposition sample. Potential aging effects of the nanoparticles on the GaAs were also studied.
9:00 PM - EE6.4
Density Functional Theory Study of the Equilibrium Crystal Shape of Tungsten Carbide.
Yang Zhong 1 , Hong Zhu 1 , Leon Shaw 1 , Ramamurthy Ramprasad 1
1 Department of Chemical, Materials & Biomolecular Engineering, University of Connecticut, Storrs, Connecticut, United States
Show AbstractDensity functional theory (DFT) computations are used to investigate the equilibrium shape of WC crystals in pure WC, WC-Co and WC-Ni systems. The study unveils that the equilibrium shapes of WC are different for the three systems investigated owing to surface energy variations with the adsorption of metal atoms on WC facets. Examination of carbon-rich and carbon-deficient conditions indicates that the shape of WC is affected by the chemical potential of carbon. The WC grains are found to be truncated prisms with the aspect ratio (i.e., the ratio of the length of the prismatic face to the thickness of the prism) ranging from 1.02 to 1.33, depending on the chemical environment around WC crystals. The predicted morphology of WC grains in the WC-Co system is reproduced by the experiment.
9:00 PM - EE6.40
Current Collapses in AlGaN/GaN Hetero-structures Studied by Deep-level Optical Spectroscopy.
Yoshitaka Nakano 1 , Yoshihiro Irokawa 2 , Yasunobu Sumida 3 , Hiroji Kawai 3
1 Institute of Science and Technology Research, Chubu University, Kasugai Japan, 2 Advanced Electronic Materials Center, National Institute for Materials Science, Tsukuba Japan, 3 , POWDEC, Oyama Japan
Show AbstractAlGaN/GaN HEMTs utilizing 2DEG carriers produced at the hetero-interface are promising devices for highly efficient power amplifiers. However, these HEMTs encounter current collapse issues, where device performance at high frequencies can be limited by the presence of deep-level defects in the AlGaN/GaN hetero-structures. To date, a correlation between the current collapses and the deep-level defects still remain uncertain. In this study, we have characterized electronic deep levels in two AlGaN/GaN hetero-structures with different current collapses, using a capacitance deep-level optical spectroscopy (DLOS) technique.The AlGaN/GaN hetero-structures were grown on a c-plane sapphire substrate under a little bit different MOCVD conditions of growth temperature (sample 1: high-temp., sample 2: low-temp.). They consisted of a GaN buffer layer, an unintentionally doped 3μm-thick GaN layer, and an unintentionally doped 20nm-thick Al0.24GaN layer. Hall-effect measurements showed typical 2DEG properties with ns of ~8x1012cm-2 and μ of ~1300cm2/Vs for both samples. From PL measurements, relative intensity ratios of the yellow band to the band-edge emission were 0.80 and 2.22 for samples 1 and 2, respectively. SiN-passivated FETs and planar SBDs based on these hetero-structures were then fabricated for electrical characterization. Current collapses were assessed on the FETs, stressing a bias voltage of 100V for 5min. Samples 1 and 2 showed a decrease by ~34 and ~68% in drain current, respectively, before and after the bias stressing. Capacitance-voltage (C-V) measurements were conducted on the SBDs with and without white light illumination (λ>380nm) from the back side with a 150W xenon lamp. Compared the photo C-V characteristics to the dark C-V ones, increased 2DEG concentrations on illumination were estimated to be at least ~7.4x1010cm-2 and ~1.5x1011cm-2 for samples 1 and 2, respectively, and are considered to be optically excited from deep-level defects to the 2DEG at the hetero-interfaces. DLOS measurements were performed on the SBDs, measuring photo-capacitance transients as a function of incident photon energy, from 0.78eV (1600nm) up to 4.0eV (300nm). The SBDs were illuminated with monochromatic light from the xenon lamp. For both samples, five photoemission states were revealed with their onsets at ~1.42, ~2.07, ~2.34, ~2.80, and ~3.23eV below the conduction band in addition to the near-band-edge emissions from GaN at ~3.4eV. In particular, sample 2 with the heavy current collapse showed high concentrations of ~2.07, ~2.80, and ~3.23 levels compared to sample 1. The 3.23eV level is attributable to the C-related deep acceptor states where C is substitutionally incorporated into the N lattice sites in GaN, whereas the 2.07 and 2.80eV levels are probably related to the interstitial C impurities corresponding to the yellow bands observed in the PL measurements. Therefore, the latter levels are likely to be associated with the current collapse issues.
9:00 PM - EE6.41
Deep-level Optical Characterization of Free-standing HVPE-GaN Substrates and MOCVD-GaN Films Using Transparent Conductive Polyaniline Schottky Contacts.
Yoshitaka Nakano 1 , Nobuyuki Matsuki 2 , Mickael Lozac'h 3 , Kazuaki Sakoda 2 , Masatomo Sumiya 2
1 Institute of Science and Technology Research, Chubu University, Kasugai Japan, 2 , National Institute for Materials Science, Tsukuba Japan, 3 , University of Tsukuba, Tsukuba Japan
Show AbstractGaN and its related materials are widely used not only in light-emitting devices but also in light-receiving devices. Among them, Schottky barrier diodes (SBDs) such as ultraviolet photodetectors and solar-blind photodiodes experience some more recent development. In general, various noble metals such as Pt, Pd, and Au have been employed to form Schottky contacts on n-GaN. On the other hand, Matsuki et al. have recently reported on photovoltaic action in high quality GaN-based SBDs using p-type conducting polymer, polyaniline doped with dimethyl sulfoxide (PANI) [1]. PANI has some advantages over these noble metals; (i) large work function (5.2-5.3eV), (ii) high transparency (>240nm), and (iii) soft fabrication process. From another viewpoint of fundamental basic research, these PANI/n-GaN-based SBDs would be very useful for understanding the nature of electronic characteristics such as deep-level defects in n-GaN by capacitance-based methods, utilizing the variation in the depletion region capacitance. In this study, we have fabricated high quality transparent SBDs based on PANI films and n-GaN, and have successfully investigated electronic deep levels in n-GaN, employing capacitance-voltage (C-V) and capacitance deep-level optical spectroscopy (DLOS) techniques [2].Two kinds of PANI/n-GaN SBDs were fabricated on a MOCVD-grown n-GaN layer (Nd: 6.3x1017cm-3) and a free-standing HVPE-grown n-GaN substrate by spin coating PANI as the transparent metal electrodes. From current-voltage measurements, both SBDs showed good rectifying behaviors with a small leakage current density and a rectification ratio of 106 - 107 at ±2 V. C-V measurements revealed effective donor concentrations Nd-Na of 6.4x1017 and 2.2x1017cm-3 for the MOCVD-grown and HVPE-grown n-GaN, respectively. Capacitance DLOS measurements were performed, by illuminating the SBDs from the top surface of the transparent PANI Schottky metal with monochromatic light [2]. The PANI/n-GaN SBDs showed a typical capacitance dispersion phenomenon at 10 - 100kHz in capacitance-frequency characteristics, which is mainly due to polarization capacitance and resistance of the conductive PANI film. So, depending on frequency, there seems to be a competition between the PANI and the n/i<>-GaN characters. DLOS measurements over these specific cut-off frequencies were found to provide some valuable information regarding deep-level states in n-GaN. Both SBDs showed at least four photoemission states with their onsets at ~1.7, ~2.2, ~2.8, and ~3.1eV below the conduction band in addition to near-band-edge (NBE) emissions of GaN at 3.4eV. However, their concentrations for the HVPE-grown n-GaN were much less than those for the MOCVD-grown n-GaN. This obvious difference between them is probably due to different concentrations of the residual C impurities in n-GaN.[1] N. Matsuki et al.: Appl. Phys. Express 2 (2009), 092201.[2] Y. Nakano et al.: Appl. Phys. Express 1 (2008), 091101.
9:00 PM - EE6.42
The Effect of Interface Polarity on Ionic Conduction.
Dillon Fong 1 , Tiffany Santos 2 , Seong Kim 1 , Peter Baldo 1 , Jeffrey Eastman 1
1 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States, 2 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractWhile many researchers have explored novel electronic phenomena occurring at polar interfaces, few studies have investigated the effect of polar interfaces on ionic conduction. We focus on nominally negatively charged interfaces in LaAlO3/SrTiO3(001) superlattices grown on DyScO3(110) by oxide molecular beam epitaxy. Such interfaces (AlO2/SrO) are expected to promote enhanced ionic conductivity along the interface by increasing the oxygen vacancy concentration in the space charge regions. We describe the results of high temperature, variable oxygen pressure in-plane conductivity measurements, employing blocking electrodes, carried out as a function of bilayer repeat length. Bilayer repeat lengths ranging from 1-20 nm are explored to investigate the impact of interfaces on conductivity. Comparisons will be made with superlattices comprised of LaO/TiO2 interfaces and superlattices grown on SrTiO3(001). Interface sharpness, as assessed by x-ray scattering, will also be discussed. Work supported by the U. S. Department of Energy under Contract No. DE-AC02-06CH11357.
9:00 PM - EE6.43
Improvement of the Photovoltaic Properties of PbS Quantum Dot-sensitized Solar Cells.
Sojiro Hachiya 1 , Qing Shen 1 2 , Taro Toyoda 1
1 Department of Engineering Science, The University of Electro-Communications, Tokyo Japan, 2 , PRESTO, Japan Science and Technology Agency (JST), Saitama Japan
Show AbstractQuantum dot (QD)-sensitized solar cells have attracted much attention because the use of semiconductor QDs have some advantages in solar cell applications[1]. PbS QDs have shown the potential to generate multiple excitons by one photon absorption of UV or visible light, so it has a possibility to obtain high conversion efficiency for solar cell applications. In this work, we report PbS QD-sensitized solar cells using successive ionic layer adsorption and reaction (SILAR) method. PbS QDs were adsorbed onto nanostructured TiO2 electrodes using SILAR method for several cycles. After adsorption of PbS QDs, the surfaces of the samples were modified with ZnS coatings[2]. Finally, sandwich structure solar cells were prepared. The counter electrode was a Cu2S film on brass[3]. Mixing of the 1M S and 1M Na2S solution (polysulfide redox system) was used as the regenerate redox couple. Photovoltaic properties were studied by using a solar simulator (AM 1.5). We found that there was an optimum SILAR cycle of PbS QDs adsorption for the photovoltaic conversion efficiency. The maximum photovoltaic conversion efficiency of 0.5% has been obtained for PbS QD-sensitized solar cells. Improvement of photovoltaic properties of PbS QD-sensitized solar cells are in progress now by changing the conditions of PbS QDs adsorption. [1]A. Nozik, Physica E Vol. 14, 115 (2002). [2]Q. Shen, J. Kobayashi, L. J. Diguna, and T. Toyoda, J. Appl. Phys. Vol. 103, 084304 (2008). [3]G. Hodes, J. Manassen, and D. Cahen, J. Electrochem. Soc. Vol. 127, 544 (1980).
9:00 PM - EE6.44
Microwave Assisted Flow Chemistry – Scale up of Nanomaterials.
Keith Porter 1 , E. Barnhardt 1
1 Synthesis Division, CEM Corp, Matthews, North Carolina, United States
Show AbstractMicrowave (MW) irradiation is a rapid heating method for the synthesis of inorganic nanoparticles due to the direct activation of the inorganic precursors which causes an increase in kinetics of nucleation and promotes particle uniformity and monodispersity. This makes it ideal for the large scale synthesis of different types of nanomaterials. This poster will focus on the synthesis and characterization of several types of nanomaterials that were prepared in a microwave flow reactor. Batch scale up will also be examined and compared to flow.
9:00 PM - EE6.45
Hydrogen Adsorption on Aluminum Clusters: An Electronic Structures Density Functional Study.
Thi Viet Bac Phung 1 , Ogawa Hiroshi 1
1 Nanosystem Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki, Japan
Show AbstractThe hydrogen storage properties of aluminum nanoclusters have been theoretically studied and compared to those of bulk aluminum system. The effect of hydrogen adsorption on the geometric and electronic structures of aluminum clusters was investigated within the framework of density functional theory (DFT) based on plane-wave. We discuss the structural, energetic, and electronic properties of hydrogenated aluminum clusters with the diameters of 5.6 Å (13-atom aluminum clusters) and 11.17 Å (55-atom aluminum clusters). We demonstrate on characteristics of binding states between aluminum and hydrogen, which results from the existence of multiple adsorption sites on the surface of clusters. Three stable positions of hydrogen atoms adsorption were determined: atop, bridge, and hollow, which show the dependency on the cluster size.In addition, we discuss the stability and mobility of hydrogen on surface, subsurface of aluminum clusters and compare to those of the hydrogen diffusion on surface and in the bulk of aluminum crystal system. This work has been supported by New Energy and Industrial Technology Development Organization (NEDO) under "Advanced Fundamental Research Project on Hydrogen Storage Materials".
9:00 PM - EE6.47
High Surface Area Boron Carbon Nitrides: Novel Fabrication and Enhanced Sorption Properties.
David Portehault 1 , Cristina Giordano 1 , Christel Gervais 2 , Irena Senkovska 3 , Stefan Kaskel 3 , Clement Sanchez 2 , Markus Antonietti 1
1 Colloid Chemistry, Max Planck Institute for Colloids and Interfaces, Potsdam Germany, 2 UPMC Univ Paris 06, CNRS, UMR 7574, Chimie de la Matière Condensée de Paris, Collège de France, Paris France, 3 Department of Inorganic Chemistry , Dresden University of Technology, Dresden Germany
Show AbstractAs a bulk material, layered hexagonal boron nitride (h-BN) exhibits well known thermal stability and chemical inertness for its implementation in protective coatings and reinforcing structures, as well as strong potential for UV lasing. Enhanced behavior is also expecting in nanoscaled compounds for gas sorption and field emission. Few studies recently demonstrated that nanostructured boron nitrides exhibit high hydrogen uptake because of strong interactions between curved surfaces and H2 molecules. It is also believed that the control of the carbon content in these systems could provide an additional way to control storage properties, as this enables modification of the nature and the energy of the bond between hydrogen molecules and the surface. However, experimental studies on sorption properties of boron carbon nitrides BxCyNz are still in their infancy because of the difficult texture control. Up to now, the highest surface area reported for porous boron carbon nitrides was 950 m2 g-1 and was obtained by block copolymer templating.[1]The study presented herein reports on a novel hard templating approach towards mesoporous boron carbon nitrides.[2] Mesoporous graphitic carbon nitride (mpg-C3N4) is used as a template. This matrix completely reacts upon heating between 800 and 1400 °C, so that no isolation step is required, providing an easy route towards these materials without purification step. Moreover, the carbon nitride matrix acts as efficient nitrogen donor and supports boron diffusion, yielding a direct copy of the template, rather than the inverse replica usually observed for common hard templating.[3] Easy tuning of the composition BxCyNzOvHw (0.15 ≤ x ≤ 0.36, 0.10 ≤ y ≤ 0.12, 0.14 ≤ z ≤ 0.32, 0.11 ≤ v ≤ 0.28) as well as of the specific surface area and the pore size distribution is achieved by temperature control. We report values of up to 1560 m2 g-1 for hierarchical materials incorporating micro and mesopores, together with high resistance against oxidation up to 700 °C. The materials are characterized by XRD, elemental analysis, solid state 11B NMR, nitrogen sorption, SEM, TEM, and TGA to provide deep understanding of the structure-property relationship in these systems. To conclude, we highlight the first experimental evidence of the influence of the composition and the textural features of boron carbon nitrides on the hydrogen sorption uptake, ranging from 0.55 to 1.07 wt.% at 77 K and 1 bar.[1] Malenfant, P. R. L.; Wan, J.; Taylor, S. T.; Manoharan, M. Nat. Nanotechnol. 2007, 2, 43-46.[2] Portehault, D.; Giordano, C.; Gervais, C.; Senkovska, I.; Kaskel, S.; Sanchez, C. Antonietti, M. Adv. Funct. Mater. 2010, 20, 1827-1833.[3] Fischer, A.; Antonietti, M.; Thomas, A. Adv. Mater. 2007, 19, 264-267.
9:00 PM - EE6.48
Interaction between SDA and Zeolite SVR Probed with High Resolution X-ray Powder Diffraction and Solid NMR Spectroscopy.
Hye Sun Shin 1 , Bit Na Ju 1 , Ik Jun Jang 1 , Sung June Cho 1
1 Department of Applied Chemical Engineering, Chonnam National University, Gwangju Korea (the Republic of)
Show AbstractZeolites have attracted great attention as a catalyst, an ion exchanger, sorbents, etc. Hydrothermal synthesis of zeolite either in acid and basic condition is simple and straightforward using structure directing agents (SDA). Recently, synthesis of TNU-9(TUN), IM-5(IMF) and SSZ-74 (SVR) was reported using diquaternary amines with different chain length. TNU-9 and SSZ-74 have 2 channels which are consisted of 10 ring structure while IM-5 has 5 channels with 10 ring structure. It was unique that the increase of the interconnecting carbon chain length between two N-methyl pyrrolidine resulted in the formation of thee corresponding zeolites, respectively. All the zeolite is believed to be closely intact with SDA. The SVR zeolite was claimed to be synthesized typically under acidic medium while TUN and IMF under basic medium. Often, Al incorporation into framework is preferred because of the catalytically active site under reaction condition. Therefore, synthesis of SVR zeolite in basic medium is necessary. In the present work, the synthesis of SVR zeolite was performed using the above mentioned SDAs under basic conditions. It was discovered that the SVR zeolite can be synthesized under basic condition using N1,N1,N1,N5,N5,N5,-hexamethylpentane-1,5-diaminium as SDA. All the Al in the SVR zeolite was located at the tetrahedral position referred from MAS 27Al NMR. Upon calcination, the octahedral species appeared. Elemental analysis showed that the Si/Al ratio was 81. The deconvolution of 29Si NMR spectrum showed the larger amount of Q3 was decreased substantially during the calcination and became similar to that reported. Such a change suggested the intimate interaction between SVR zeolite framework and SDA. For the structural determination of powder diffraction of the high quality SVR zeolite, the initial coordinate of the framework of the SVR zeolite was generated using chargeflip method employing the reported framework structure as model structure. Initial structure of SDA and zeolite framework was obtained using parallel tempering implemented in Free Object for X-crystallography while the initial structure of SDA was optimized by MM2 method. The final Rietveld refinement was performed using GSAS program suite with the soft constraint on bond distances. The obtained Rp, Rwp, and RF, were 7.44%, 9.61% and 3.55%, respectively.The SDA was found to be close intact with siloxy group where N3-O3=3.32 Å and N11-O33=3.88 Å, respectively. The silanol/siloxy nest had multiple bonds like O3-O16=2.62 Å, O3-O32=2.61 Å, O16-O33=2.76 Å, O16-O33=2.76 Å and O32-O33=2.69 Å.Combination of parallel tempering with Rietveld refinement suggested the intriguing structure of SDA and corresponding zeolite. It was confirmed the presence of the ordered Si vacancy and the Al can be incorporated into the framework of the zeolite otherwise it is difficult to obtain. Therefore, the acid catalysis employing Al site in the SVR zeolite can be possible.
9:00 PM - EE6.49
Reaction Mechanism of Surface Oxide Layer Elimination on the Surface of Tin Alloy Particle for the Synthesis of Environmental Friendly Electric Integrated Materials.
Yozo Shimada 1 , Hideyuki Takahashi 1 , Takeshi Tanaka 2 , Masakazu Hamada 2 , Kazuyuki Tohji 1
1 Graduated school of Environmental studies, Tohoku University, Sendai Japan, 2 , Ishikawa Metal Co.,Ltd, Sakai Japan
Show AbstractElectronics devices had been integrated on the circuit board by using solder paste which consisted by solder particles and flux, such as pine resin and surfactant. Solder paste should be contained large amount of halogen species to show the high performance for integration. Taking the recent effort for developing the environmentally friendly products into consideration, halogen free solder paste should be developed. Most important role of halogen was elimination of oxidized layer of solder particle surface. Thus, it can be considered that the lowering of the amount of oxidized layer of solder particles will read the lowering the necessary amount of flux, in other word, necessary amount of halogen surfactant. Moreover, it also considered that the surface of the solder particle with lowered oxidized layer should be stable against to re-oxidation. In this research, the reaction mechanism of the elimination of oxide layer on the surface of solder particles was investigated through the reaction between the halogen flux and tin oxide on the solder particle surface. Lead free solder (SnAgCu) particles was introduced into Br surfactant / hexyldiglycol solution, and kept for 5-10 days under 35 degree C. The concentration of Br surfactant was varied from 750-15000ppm against to 30g of solder particles. In some cases, other regent, such as organic material and water, was added to the solution to evaluate these effects to the oxidation. After treatment, treated particles were collected and well washed with toluene to remove the organic materials remained on its surface, and evaluated by the XPS with Ar etching (to measure the depth profile), SEM-EDX and HR-TEM. In the case of un-treated powder without Ar etching, only the peak of tin oxide was apparently observed, and it was clearly detected until 6 times Ar etching. On the other hand, in the case of treated powder, tin metal peak was observed regardless of no surface etching, and the tin oxide peak disappeared within 2 times Ar etching. These results indicated that the thickness of surface tin oxide layer is decreased by this treatment. Thus, oxide layer of solder particles could be successfully removed by halogen surfactant/ hexyldiglycol solution.By increasing the concentration of halogen surfactant, either single or few layers thick Sn-Br compounds were synthesized on the surface of solder particle. This layer stabilized the solder particles against re-oxidation. Halogen content was a function of particle size and distribution. Solder paste prepared using powder treated with the proposed technique and non halogen surfactant, showed excellent performance for integration, regardless a halogen content of 70-180 ppm. Further lowering of halogen content can be anticipated by tuning the solder particle size and distribution.
9:00 PM - EE6.5
Neodymium Element Doped Ceramics for Electrically Controlled Random Lasing and Anderson Localization.
Xiudong Sun 1 , Jingwen Zhang 1 , Hua Zhao 1 , Yingyin Zou 2 , Kewen Li 2 , Hua Jiang 2 , Xuesheng Chen 3
1 Physics, Harbin Institute of Technology, Harbin, Heilongjiang, China, 2 , Boston Applied Technologies, Inc., Woburn, Minnesota, United States, 3 Physics and Astronomy, Wheaton College, Norton, Massachusetts, United States
Show AbstractConventional lasers are based on optical gain media and laser cavities that trap light for long enough for lasing action to occur.[1] In newly developed laser sources, random lasers, the roles played by regular cavities in conventional ones are taken over by strong diffusive nature in materials such as a fine powder.[2] In a random laser, light waves are trapped by multiple light scattering. In Ref [2], by using a liquid crystal inside a disordered material, it was made possible to have external control over the diffusion constant, and hence random lasing action. In the past decade, another research highlighted area is of photon Anderson localization.[3] It is highly desirable to design optical material systems in which both random lasing and Anderson localization can be realized, and consequently, the correlation between the two would be studied accordingly. Here, we report random lasing action in a ceramic plate of neodymium doped lanthanum-modified lead zirconate titanate (Nd3+:PLZT). In addition, strong electrically controllable scattering was observed and its great impact on the random lasing action was evidenced. The strong electro-induced scattering could be used to study Anderson localization. By choosing a four energy level system, Nd3+:PLZT, as laser gain medium, lasing action was seen recently.[4] Along this line, obvious random lasing characteristics were demonstrated with this material system. The gain medium used was 1.0 mol % in Nd3+ doping concentration, 3.0 mm × 3.0 mm × 2.0 mm in dimension. The slug from which the specimen was cut consisted of 65 mol % lead zirconate plus 35 mol % lead titanate and 10 mol % lanthanum in the form of La2O3, to which 1.0 mol % Nd3+ cations had been added in the form of Nd2O3. A typical sintering process of the ceramic was used to synthesized the ceramics The pumping source was a fiber-pigtailed and water-cooled high-power laser diode of 805 nm center wavelength, operating at its pulse mode. Intensive research activities to improve power and stability of the laser output are still undergoing and will be reported.A very intriguing feature of the Nd3+:PLZT laser dynamics was observed, similar to the observation in performing optical amplification. These observations suggested a long persistent energy storage mechanism equivalent to a long lifetime of the upper manifold. This property is highly desirable for high-power lasers, which is the ultimate objective of this project. The energy thus released, if can be accumulated, can increase the peak power of ceramics random laser tremendously. Anomaly optical amplification for weak seed light was analyzed with a picture of random lasing.[1] M. A. Noginov, “Solid-State Random Lasers”, 2005 Springer Science Business Media Inc [2]. D. S. Wiersma, and S. Cavalieri, Nature, 414, 708-709 (2001)[3] A. Lagendijk, B. V. Tiggelen, and D. S. Wiersma, Phys. Today, 24-29, (2009)[4] J. W. Zhang, et al, CTuFF3, CLEO/IQEC, Baltimore, Maryland, USA, 2009
9:00 PM - EE6.7
Novel lead-free Bi-based Tetragonal Ferroelectric Films Grown by MOCVD.
Hiroshi Funakubo 1 , Shintaro Yasui 1 , Junichi Nagata 1 , Keisuke Yazawa 1 , Tomoaki Yamada 1 , Hiroshi Uchida 2
1 , Tokyo Institute of Technology, Yokohama Japan, 2 , Sophia University, Tokyo Japan
Show AbstractFerroelectric materials have been widely investigated not only to conventional memory and piezoelectric applications, but also to energy harvesting and micro electro optical devices. Tetragonal ferroelectric materials are most fundamental ones, such as BaTiO3 and PbTiO3. Especially PbTiO3 is an important as the end member of the piezoelectric materials having large response, such as PbTiO3-PbZrO3 (PZT), PbTiO3-Pb(Mg1/3Nb2/3)O3 and so on, because the phase boundary between tetragonal and non-tetragonal symmetries showed maximum piezoelectric response. However, the lead-free materials are essential for the environmental friendly “green materials” requirement. BaTiO3 is well known lead-free tetragonal material but its Curie temperature is low as 120oC that limit the real applications. There are some reports on the synthesis of Bi-based tetragonal ferroelectrics materials using high pressure synthesis since 2000, but its ferroelectricity has been hardly reported experimentally. In the present study, we reports for the first time on the growth of epitaxial tetragonal films of Bi(Zn1/2Ti1/2)O3 - Bi(Mg1/2Ti1/2)O3 - BiFeO3 systems by MOCVD on (100)cSrRuO3//(100)SrTiO3 substrates. Tetragonal films with the lattice parameter ratio of c- and a-axes, c/a ratio, from 1.22 to 1.07 were systematically obtained by changing composition ratio of Bi(Mg1/2Ti1/2)O3 and Bi(Zn1/2Ti1/2)O3 in 0.66{Bi(Zn1/2Ti1/2)O3 - Bi(Mg1/2Ti1/2)O3}-0.34BiFeO3 systems. Perfectly (001) polar-axis oriented epitaxial films growth were ascertained by the XRD reciprocal space mappings as well as the lateral and vertical piezoresponse force microscopy (PFM) observations. These shows good insulating characteristics and clear saturated hysteresis loops originated to ferroelectricity were obtained for the films with the c/a ratio below 1.07 and its saturation polarization (Psat) value was 65 μC/cm2. Apparent d33 value obtained by PFM was about 70 pm/V. In addition, its Curie temperature was ascertained to be higher than that of PbTiO3. These results open the door for novel type of lead-free ferroelectric materials as well as the piezoelectric materials.
Symposium Organizers
P. Shiv Halasyamani University of Houston
David G. Mandrus The University of Tennessee/Oak Ridge National Laboratory
Kyoung-Shin Choi Purdue University
Simon J. Clarke University of Oxford
EE7: Iron-based Superconductors, Magnetic Materials and Structural Analysis
Session Chairs
Wednesday AM, December 01, 2010
Ballroom A, 3rd floor (Hynes)
9:30 AM - **EE7.1
Lattice Effects in Iron Pnictide Superconductors (25 min.).
Dirk Johrendt 1 , Marianne Rotter 1 , Marcus Tegel 1
1 Department of Chemistry, Ludwig-Maximilians-Universität, München Germany
Show AbstractThe discovery of superconductivity in a series of layered iron pnictides1-4 has revived the research in the field of high-Tc materials. Enormous progress has already been achieved, which has manifested the diversity of these materials, where superconductivity, magnetism and structural chemistry are intimately connected. Currently, a number of experiments5,6 support an unconventional pairing mechanism based on the s±-scenario.7 The latter relies on Fermi surface nesting, which in turn depends on subtle details of the crystal structure. In this context, it is becoming apparent that the role of the atomic structure on the high-Tc phenomenon is more fundamental in pnictides than in cuprates.8 Examples are the structural changes close to Tc in Nd(O1-xFx)FeAs,9 the extreme sensitivity of the Fe-As bonds on the magnetic moment in charge neutrally doped BaFe2(As1-xP)2,10 and the unusual response of the lattice to superconductivity in Co-doped Ba(Fe1-xCox)2As2.11 The latter compound also exhibits co-existence of superconducting and magnetic order parameters at the atomic scale, which is still controversial in the case of Ba1-xKxFe2As2,12,13 although there is no chemical evidence for an intrinsic inhomogeneity. Even though the detailed physical significance is partly still unclear, we suggest that the lattice anomalies are some kind of response to unconventional superconductivity as well as the co-existence with magnetism, and careful studies might reveal relevant information on the mechanism. This talk gives a brief synopsis on the field and presents results of high-resolution X-ray and neutron diffraction as well as 57Fe-Mössbauer experimemts with BaFe2(As1-xP)2, Ba1-xKxFe2As2 and Sr2VO3FeAs14 in order to shed light on the relationships between structure and superconducting properties. 1 Y. Kamihara, T. Watanabe, et al., J Am Chem Soc 130, 3296 (2008).
2 M. Rotter, M. Tegel, and D. Johrendt, Phys Rev Lett 101, 107006 (2008).
3 X. C. Wang, Q. Q. Liu, et al., Solid State Commun 148, 538 (2008).
4 D. R. Parker, M. J. Pitcher, et al., Chem Comm 16, 2189, (2009).
5 T. Hanaguri, S. Niitaka, K. Kuroki, et al., Science 328, 474 (2010).
6 A. D. Christianson, E. A. Goremychkin, et al., Nature 456, 930 (2008).
7 I. Mazin, D. Singh, M. Johannes, et al., Phys Rev Lett 101, 057003 (2008).
8 T. Egami and S. J. L. Billinge, Prog Mater Sci 38, 359 (1994).
9 M. Calamiotou, I. Margiolaki, A. Gantis, et al., arxiv:1004.1340.
10 M. Rotter, C. Hieke, and D. Johrendt, arXiv:1005.1411 (PRB, in press).
11 S. Nandi, M. G. Kim, et al., Phys Rev Lett 104, 057006 (2010).
12 H. Fukazawa, T. Yamazaki, et al., J Phys Soc Jpn 78, 033704 (2009).
13 M. Rotter, M. Tegel, I. Schellenberg, et al., New J Phys 11, 025014 (2009).
14 M. Tegel, F. Hummel, Y. Su, et al., EPL 89, 37006 (2010).
10:15 AM - EE7.3
Chemical Control of the Superconductivity in NaFeAs and LiFeAs Derivatives.
Simon Clarke 1 , Michael Pitcher 1 , Dinah Parker 1 , Jack Wright 2 1 , Tom Lancaster 2 , Stephen Blundell 2 , Francis Pratt 3 , Peter Baker 3
1 Chemistry, University of Oxford, Oxford United Kingdom, 2 Physics, University of Oxford, Oxford United Kingdom, 3 ISIS facility, STFC, Didcot, Oxfordshire, United Kingdom
Show AbstractThe correlation of composition with structure and physical properties will be described for the “111” series of alkali metal iron pnictides AFeAs (A = Li, Na). A combination of high resolution X-ray and neutron powder diffraction, muon-spin rotation spectroscopy and magnetometry measurements will be described which probe the competition between superconductivity and antiferromagnetism in stoichiometric NaFeAs and the cobalt- and nickel-doped derivatives focusing particularly on the region of compositions where magnetic order and superconductivity are present in the same sample. The behavior of these systems in which a superconducting dome is traversed as 0.1 electrons per Fe atom are added to the stoichiometric NaFeAs system will be discussed in relation to other classes of iron pnictide superconductors. The behavior of the doped NaFeAs system will be contrasted with the behavior of the doped LiFeAs system, for which the stoichiometric composition shows the optimal superconducting properties. The extremely high sensitivity of the LiFeAs system to composition and Li/Fe disorder will also be described. The differences in behavior of the NaFeAs and LiFeAs systems and the differing responses of the electronic properties of the two systems to applied hydrostatic pressure will be related to the structural parameters.
10:30 AM - EE7.4
Giant Magnetoresistance in Oxypnictides (La,Nd)OMnAs.
Abbie Mclaughlin 1 , Eve Wildman 1 , Jan Skakle 1 , Gaetan Giriat 2 , Ron Smith 3 , Nicolas Emery 1
1 Chemistry, University of Aberdeen, Aberdeen United Kingdom, 2 , University of Edinburgh, Edinburgh United Kingdom, 3 , ISIS facility, Chilton,Didcot United Kingdom
Show AbstractThe magnetic, electronic and structural properties of the oxypnictides (La,Nd)OMnAs will be presented. Results from SQUID magnetometry and neutron diffraction show that both materials are weak ferromagnets with transition temperatures above room temperature (Tc = 317 and 335 K for Ln = La and Nd respectively). Both compounds crystallise in space group P4/nmm where insulating layers of (La3+/Nd3+O2)+ are embedded between layers of tetrahedral (MnAs)- and there is no evidence of a structural transition down to 4 K. LnOMnAs (Ln = La, Nd) are semiconducting and a sizeable negative magnetoresistance (MR) is observed. MR up to -24 % is observed at 200 K for LaOMnAs in a 5 Tesla field which is unprecedented for divalent Mn2+. The magnetoresistance is very sensitive to electronic disorder and we suggest that the sizeable –MR arises as a reduction in quantum destructive interference with field.
10:45 AM - EE7: Magnetism
BREAK
11:15 AM - **EE7.5
Magnetic and Superconducting Properties of Fe-based Superconductors: A First Principles Perspective.
Michelle Johannes 1 , Igor Mazin 1 , David Singh 3 , Lilia Boeri 4 , Klaus Koepernik 2
1 Center for Computational Materials Science, Naval Research Laboratory, Washington, District of Columbia, United States, 3 , Oak Ridge National Lab, Oak Ridge, Tennessee, United States, 4 , Max Planck Institute fur Festkorperforschung, Stuttgart Germany, 2 , IFW Dresden, Dresden Germany
Show AbstractThe newly discovered Fe-based superconductors have the highest transition temperature outside of the cuprate class. The parent compounds have amagnetic state which must be suppressed, either by doping or by pressure, in order for superconducitivity to occur. This suggests a competitiverelationship between long-range magnetic order and superconductivity. Density functional theory has been very successful in reproducing many of the observed characteristics of these materials, from the ARPES-observed Fermi surface, to the spin density wave stripe magnetic order and the smallstructural distortion that occurs prior to the magnetic order. Although the symmetry of the superconducting state is not fully settled, the most likely candidate, the s+/- state was inferred from the results of density functional calculations. However, there are discrepancies between DFT derived properties and those measured by experiment. In DFT, the imposition of the magnetic state is necessary in order to reproduce the structural distortion, despite the fact that the latter occurs higher in temperature than the former. Once the magnetic state is established, even small structural details match extremely well between calculation and experiment. However, the magnetic moment itself is strongly overestimated at zero pressure and dies down too slowly as a function of pressure.In this talk, I will review the basic properties of the Fe-based superconductors, discuss the important results produced by DFT calculations and show what can be learned not only from what DFT gets right, but also from what DFT gets wrong.
11:45 AM - EE7.6
Magnetic Ordering in Rare-earth Chromium Sulphides.
Anthony Powell 1 , Iwona Szkoda 1 , Rodolfo Sanchez 2 , Paz Vaqueiro 1
1 Chemistry, Heriot-Watt University, Edinburgh United Kingdom, 2 , Centro Atomico Bariloche, Bariloche Argentina
Show AbstractThe high and variable coordination number of rare-earth cations offers a degree of structural complexity that goes beyond that in materials containing main-group or transition-metal ions with well-defined coordination preferences. Furthermore, in materials containing both rare-earth and transition-series cations, the simultaneous presence of d- and f-block elements allows three types of electron-electron interaction, d-d, d-f and f-f, to be simultaneously present. The opportunity for unusual structural and physical properties that this presents has led us to explore new ternary rare-earth transition-metal sulphides.We recently reported the structural properties of a series of erbium chromium sulphides. Single-crystal X-ray diffraction studies of Er2CrS4, Er4CrS7 and Er6Cr2S11 led us to identify a common M2S5 (M = Cr, Er) building unit in these materials. The structures consist of M2S5 slabs of varying thickness, linked by single octahedral chains. The materials may thus be considered as members of a homologous series, possessing a common anionic framework, [M2n+1S4n+3]x-, in which charge balancing is provided by additional rare-earth cations. To date, we have prepared materials corresponding to the n = 1, 2, 3 and ∞ members of this family. In the related material Er3CrS6, the slabs are absent, and Cr3+ ions are ordered into single octahedral chains.Magnetic susceptibility data for these materials suggested that the presence, or otherwise, of long-range magnetic order is related to the degree of Er/Cr ordering in the structure: anomalies being observed in the low-temperature susceptibility of all phases except Er4CrS7. Here, we will present the results of an investigation of long-range magnetic order in these phases by powder neutron diffraction. The results demonstrate that Er4CrS7, in which erbium and chromium cations are disordered over the sites in the M2S5 slab, remains paramagnetic to 2K. Er6Cr2S11, which is also disordered but has a slightly higher concentration of chromium cations within the M2S5 slab, exhibits ordering of the Cr2+ cations only. For Er2CrS4 and Er3CrS6, which show full cation ordering, variable temperature powder neutron diffraction data reveal two magnetic transitions. These are associated with successive ordering of the chromium and erbium sub-lattices on cooling. The complex magnetic structures of these phases have been established using the techniques of representational analysis in conjunction with powder neutron diffraction data.
12:00 PM - EE7.7
Real Space Investigation of Structural Changes at the Rutile VO2 Metal-insulator Transition.
Serena Corr 1 , Daniel Shoemaker 2 , Brent Melot 2 , Ram Seshadri 2
1 School of Physical Sciences, University of Kent, Kent United Kingdom, 2 Materials Research Laboratory, University of California, Santa Barbara, California, United States
Show AbstractThe electrical property changes in rutile VO2 raise a number of interesting questions, particularly the structural nature of the material at the transition temperature. Here, we describe synchrotron x-ray total scattering studies and reverse Monte Carlo simulations of the structural changes occurring in rutile VO2 as it goes through its metal-insulator transition. On cooling through 340 K, rutile VO2 goes from a high temperature tetragonal phase to a low temperature monoclinic phase, characterized by a pairing and tilting of the V-V ions along the c-axis. While previous studies have found nanoscale phase separation, it has remained unclear whether these domains are made up of the two bulk phases or represent some distinct intermediate phase. We have probed the local structure changes in the bulk material using Pair Distribution Function (PDF) techniques and have found that at the transition temperature there exists an equilibrium mixture of the low-temperature monoclinic and high-temperature tetragonal phases. We demonstrate that the first-order transition occurs with no evidence of short-range V–V correlations in the high temperature phase. This report of a structural study at the nanoscale shows for the first time that there are only two distinct phase populations.
12:15 PM - EE7.8
α (Spinel) to β (CaFe2O4-type) Transformation at HP & HT in CdCr2O4: Structural Mechanism and Magnetic Properties.
Miguel Angel Alario-Franco 1 , Angel Arevalo-Lopez 1 , Antonio Dos santos-Garcia 1 , Elizabeth Castillo-Martinez 1 , Alejandro Duran 1
1 Facultad de Ciencias Quimica, Uiversidad Complutense de Madrid, Madrid, Madrid, Spain
Show AbstractWe have successfully transformed the α-CdCr2O4 spinel-type structure to its high-pressure β-polymorph with the CaFe2O4-type structure. We propose a novel structural transformation mechanism between the two structures. Because the β-CdCr2O4 structure includes both edge- and corner-sharing [Cr-O6] octahedra, a competition between the magnetic exchange interactions is inherent to it and complex magnetic properties are expècted in these types of arrangements. In the present case, the magnetic and heat capacity data of β-CdCr2O4 indicate a low-dimensional transition with a maximum centered at 100 K that demonstrates the Cr-O-Cr interactions. Two more transitions are observed at 25 and 10K when the Cr-Cr interactions develop a complex AFM order.(1)
[email protected].; http://www.ucm.es/info/labcoap/index.htm
12:30 PM - EE7.9
Total Scattering Descriptions of Local and Cooperative Jahn-Teller Distortions in the CuxMg1-xCr2O4 Solid Solution.
Daniel Shoemaker 1 , Ram Seshadri 1
1 Materials, UC Santa Barbara, Santa Barbara, California, United States
Show AbstractThe coordination of spinel A-site cations in the solidsolution between tetragonal CuCr2O4 andcubic MgCr2O4 has been investigated by large-box reverse Monte Carlo (RMC) fits to thepair distribution function (PDF) obtained from neutron totalscattering. Cu2+ cations on the A site of MgCr2O4 could be expected to havea locally distorted Jahn-Teller environment,even when the average structure remains cubicas x → 0.We show thatCu2+ forms significantly more distortedcoordination environments than Mg2+ on the same crystallographicsite, even in compounds thatare a single crystalline phase as determined by Rietveld refinement. We find that local distortions remain prevalentin cases where long-range orbital ordering producesa cooperative Jahn-Teller distortion.The ability to probe distinct atomic coordination by chemicalspecies is accomplished by modeling an RMC supercell with distinct Cu and Mg atoms, rather than a singleunit cell with fractional occupancy.We presentnew metrics for the quantification of PDF data via continuoussymmetry measures and explore how cation coordinationcan be systematically tracked as a function of temperatureand composition.
12:45 PM - EE7.10
Nanocheckerboard Modulations in (NaNd)(MgW)O6.
Mark Licurse 1 , Peter Davies 1
1 Materials Science and Engineering, Univ. of Pennsylvania, Philadelphia, Pennsylvania, United States
Show AbstractThis presentation is focused on (NaNd)(MgW)O6, one of several (A’A”)(B’B”)O6 perovskites with both A- and B-site ordering. The ordered A-site (A’A”)BO3 perovskites have received increased attention following the observation of unusual periodic nanoscale phase separation in the (Nd2/3-xLi3x)TiO3 system [1]. The tunable superlattice consists of diamond-like domains of the Li-rich end-member (NdLiTi2O6) separated by Li-free regions of Nd4/3Ti2O6. The phase separation leads to a nanocheckerboard strain pattern observed in high-resolution transmission electron microscopy (HRTEM) images. Recently new examples of compositional modulation were observed in Li-free perovskites. For (NaLa)(MgW)O6 the modulation occurs in one dimension leading to a striped pattern of light and dark regions. For (NaNd)(MgW)O6, selected area electron diffraction (SAED) patterns along [001] show sharp, well-defined satellites grouped around the primary perovskite reflections indicating the presence of a highly ordered 14ap x 14ap superstructure with modulations along the g100 and g010 directions. HRTEM images show the resulting checkerboard pattern of light and dark regions consistent in size and orientation with the aforementioned SAED patterns. Thinner regions of the grains highlight square nanodomains with edges parallel to (110) and (1-10). Within the domains additional fringes corresponding to a doubled (110) plane d-spacing are evident along both (110) directions. The images also reveal an anti-phase relationship between the doubled (110) spacings in adjacent domains. Finally, Z-contrast images confirm the presence of a compositional modulation. For the related system (NaLa)(MgW)O6, compositional analyses indicated phase separation into (NaLa)(MgW)O6 and La4/3(MgW)O6 forming the striped pattern. This model was justified by assuming local variations in composition and/or Na-loss during high-temperature synthesis. A similar argument for (NaNd)(MgW)O6 would give regions of (NaNd)(MgW)O6 and Nd4/3(MgW)O6. However, through the use of sacrificial powders we believe Na-loss was suppressed. Furthermore, both Na2WO4 and its hydrate, Na2WO4-2H2O, were found in small concentrations by synchrotron x-ray diffraction suggesting the stable end-member is not (NaNd)(MgW)O6. If phase separation produces this compositional modulation, determination of the end members could allow for a tunable nanostructure. Identification of these end-members and the structural details of this system will be discussed.[1]. This and other references can be found in M. W. Licurse & P.K. Davies, Applied Physics Letters (in press, 2010).
EE8: Ferroelectricity, Ferromagnetism and Materials for Energy Applications
Session Chairs
Miguel Alario-Franco
Michelle Johannes
Wednesday PM, December 01, 2010
Ballroom A, 3rd floor (Hynes)
2:45 PM - EE8.1
The Search for Multifunctional Polar Materials.
Joseph Bennett 1 , K. Rabe 1
1 Physics and Astronomy, Rutgers University, Piscataway, New Jersey, United States
Show AbstractThe search for polar, potentially magnetic materials is sometimes hindered by a lack of reported data. In most cases, a polar space group is given, but neither polarization or band gap measurements are available because the material is too conductive. Using a combination of databases and symmetry analysis, we would like to first identify potentially interesting polar materials and screen out those that are reported to be metallic. Those that remain, and are of interest, are generally materials that contain main group elements, display a semiconductive band gap and show some degree of magnetic coupling. We then use first-principles density functional theory (DFT) calculations to investigate the ground state structures of these experimentally synthesized materials for which limited data is available. These calculations will help us to understand if, why and how the material may be polar, magnetic and semiconductive.
3:00 PM - EE8.2
Effect of Mn Coordination on Dielectric and Magnetic Responses in Mn-doped Perovskite-like Incipient Ferroelectrics.
Paula Vilarinho 1 , Alexander Tkach 2 1 , Abilio Almeida 2 , Igor Levin 3 , Victor Krayzman 3 , Joseph Woicik 3
1 Dep. of Ceramics and Glass Engineering, University of Aveiro, Aveiro Portugal, 2 Department of Physics of Science Faculty, University of Porto, Porto Portugal, 3 Ceramics Division, National Institute of Standards and Technology, Gaithersburg, Maryland, United States
Show AbstractThere is currently a renewed interest in magnetoelectric properties of materials triggered by the discovery of novel multiferroics with potentially large magnetoelectric susceptibilities[1] and possible electrical control of magnetic ordering, permitting data storage and processing with low power consumption[2]. Within this context, dielectric and magnetic anomalies were recently found to be coupled in Sr1-xMnxTiO3 according to the so called “multiglass” scenario, where freezing of the electric dipoles, created by off-center Mn2+Sr ions in a highly polarizable SrTiO3 lattice, initiates the transition of the magnetic Mn2+ spin moments into a spin glass state at the dipolar glass temperature Tg=38K[3]. The low-temperature dielectric relaxation was also reported in single crystals of another incipient ferroelectric, Mn-doped KTaO3 and attributed to off-center displacement of Mn2+ from K site along one of the six <001>-type crystal directions[4]. On the other hand, the dielectric response of K1-2xMnxTaO3 ceramics in the microwave range have shown only weak relaxations in dielectric losses, but not in real part of the permittivity[5], whereas magnetic response was completely attributed to Mn3O4 secondary phase starting form x=0.01[6]. Most recently, the spin glass behavior was observed in K1-xMnxTaO3 (x=0.03) ceramics[7], although so far no research on the coordination and solubility limit of Mn in of K1-xMnxTaO3 has been undertaken.In this work the effect of Mn coordination on the dielectric and magnetic responses in Mn-doped perovskite-like incipient ferroelectrics, SrTiO3 and KTaO3 is addressed. Ceramic samples with the nominal Sr1-xMnxTiO3, SrTi1-yMnyO3, K1-xMnxTaO3 and KTa1-yMnyO3 (with x and y [0 - 0.03]) compositions were studied. The coordination of Mn was analyzed using X-ray absorption fine structure (XAFS) measurements that can directly probe local coordination environment of dilute species. The structural data was related to the dielectric and magnetic responses of both systems. XAFS provides direct evidence for the presence of strongly off-centered Mn cations on the A-sites of the perovskite incipient ferroelectric lattices thereby supporting the models to explain dielectric and magnetic relaxation.[1]W. F. Brown, R. M. Hornreich, S. Shtrikman, Phys. Rev. 168 574 (1968). [2]X. Chen, A. Hochstrat, P. Borisov, W. Kleemann, Appl. Phys. Lett. 89 202508 (2006).[3]V. Shvartsman, S. Bedanta, P. Borisov, W. Kleemann, A. Tkach, P. M. Vilarinho, Phys. Rev. Lett., 101, 165704 (2008).[4]V. V. Laguta, M. D. Glinchuk, I. P. Bykov, J. Rosa, L. Jastrabik, M. Savinov, Z. Trybula, Phys. Rev. B, 61, 3897-904 (2000).[5]A.-K. Axelsson, Y. Pan, M. Valant, N. M. Alford, J. Am. Ceram. Soc., 93, 800-5 (2010).[6]M. Valant, T. Kolodiazhnyi, A. Axelsson, G. S. Babu, N. M. Alford, Chem. Mater. 22, 1952-4, (2010).[7]V. V. Shvartsman, S. Bedanta, P. Borisov, W. Kleemann, A. Tkach, P. M. Vilarinho, J. Appl. Phys. 107, 103926 (2010).
3:15 PM - EE8.3
Palmierites: Manipulating Transition Metal Oxides for Conductivity.
Eve Wildman 1 , Abbie Mclaughlin 1 , John Hanna 3 , John Irvine 2 , Jan Skakle 1
1 Chemistry/Physics, University of Aberdeen, Aberdeen United Kingdom, 3 Physics, Warwick University, Coventry United Kingdom, 2 Chemistry, University of St. Andrews, St. Andrews United Kingdom
Show AbstractPalmierite, A3M2O8 is a distant relative of perovskite, in that it is comparable to the 9R BaRuO3 type structure. Oxygen (and M cation) vacancies give rise to tetrahedral M coordination, and give the formula Ba3M2■O9-x, where x=1 and ■ represents a vacancy on the M site. As perovskites have, over the years, proved such a fertile ground for exciting new materials, palmierites may also be considered a promising area of research. Much research to date has concentrated on the phosphates, Ba3P2O8 and Ca3P2O8 which are ionic conductors; however the conductivity was thought to be via the Ba2+ and Ca2+ ions rather than oxide ions. The barium phosphate also showed some electronic conduction. Recent work on the phosphate-vanadate join has suggested a gradual change from ionic to electronic conduction, and therefore tailoring mixed conduction properties may be feasible. Here, however, we are primarily interested in transition metal palmierites. Our earlier research started with the vanadate, which is a rather stable insulator, although the calcium vanadate is a high temperature ferroelectric. We have therefore synthesised and characterised a range of solid solutions in the Ba3M2-xM'xO8+δ system, and have been able to follow the development of electrical properties with composition. Many interesting features have been observed, including the stabilisation of tetrahedral Cr3+ in the V/Cr system and the induction of semiconductor behaviour in the V/Mn materials. In addition, we have revisited Ba3Nb2O8 and shown, definitively, that this is not a palmierite, counter to existing reports. Solid state nmr and neutron diffraction confirms that this material more closely resembles an oxygen deficient perovskite, with octahedral Nb and no major displacement of Nb ions. Finally, we have identified a series of new compositions in the palmierite system with promising conductivities, together with good thermal stability (both with atmosphere and with time). These latter materials have great potential for fuel cell applications and are currently being investigated further.
4:00 PM - **EE8.4
Phase Equilibrium Studies of Oxide Systems for Energy Applications.
Terrell Vanderah 1 , I. Levin 1
1 Ceramics Division, NIST, Gaithersburg, Maryland, United States
Show AbstractCurrent phase equilibrium research at NIST includes studies of systems pertinent to solid oxide fuel cell (SOFC) applications as well as nuclear waste. For SOFC applications, the system Nd2O3-Sm2O3-CeO2 was determined following reports of promising ionic conductivities at reasonable temperatures in (Nd,Sm)-doped ceria. This system is dominated by an extensive CeO2-based solid-solution field. Electron-diffraction studies of local atomic ordering in this phase field will be described. In the area of nuclear energy, the SrO-Y2O3-ZrO2 and SrO-Y2O3-TiO2 equilibrium phase diagrams were determined as they are pertinent to the immobilization and processing of nuclear waste. Although nuclear reactions produce an abundance of radioactive isotopes with a variety of half-lives and decay pathways, one of particular interest for biological reasons is strontium-90, which decays first to yttrium and then to zirconium. The equilibrium SrO-Y2O3-ZrO2 phase diagram will support identification of the phase assemblages that may evolve with time and heat during the Sr>Y>Zr decay sequence in a ceramic oxide matrix. The analogous diagram was determined with TiO2 since titanate-based ceramics are being considered as host materials for the storage of radioactive waste.
4:30 PM - EE8.5
Stereo-active Lone-pair Control on the Ferromagnetic Behavior in VO(SeO2OH)2 – A New Acentric Ferromagnetic Material.
Sang-Hwan Kim 1 , P. Halasyamani 1 , Athena Sefat 2
1 Chemistry, University of Houston, Houston, , Texas, United States, 2 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractWe have synthesized a new acentric ferromagnetic material of VO(SeO2OH)2. The crystal structure and functional properties have been characterized using single crystal X-ray diffraction, DC-magnetization, and second harmonic generation (SHG) measurements. The structure exhibits linear chains of corner-shared V4+O6 octahedra separated by SeO2OH groups. The material exhibits a weak SHG efficiency. We observed a ferromagnetic transition occurred at ~ 2.5K. The origin of the ferromagnetism has been elucidated by the suppression of the super-exchange (SE) interactions in the intra-chain and super-super-exchange (SSE) interactions through the inter-chain. In addition, we firstly show that the SSE interactions depend on the angle of O(2)–Se4+–O(3) using first principles density functional theory (DFT) calculations. As we demonstrate, the stereo-active lone-pair on Se4+ is the driving force for the inter-chain ferromagnetic interactions.
EE9: Poster Session: Solid State Inorganic Materials Chemistry VIII
Session Chairs
Thursday AM, December 02, 2010
Exhibition Hall D (Hynes)
9:00 PM - EE9.10
Orientational Ordering in Aqueous Clay Gels and/or Glasses
Elisabeth Hansen 1 , Henrik Hemmen 1 , Jon Otto Fossum 1
1 Physics, NTNU, Trondheim Norway
Show AbstractThis abstract concerns self-organized order in colloidal dispersions of clay nanoplatelets promoted through solvent evaporation, and how sol-to-gel and/or liquid-to-glass transitions affect the ordering process. Ever since Onsager’s now classic paper from 1949 [1], it has been known that entropic forces alone can account for the spontaneous transition of a system of hard colloidal rods from an isotropic to an anisotropic state (later confirmed to be valid also for systems of hard platelets [2]). Onsager showed that the loss of orientational entropy accompanying the emergence of order is outweighed by a simultaneous gain in translational entropy, provided the system in question is dense enough and the ordering particles sufficiently anisotropic. Langmuir had already explored experimentally the transition from a disordered to an ordered state in aqueous clay suspensions interacting also through long-range forces in 1938 [3], but could not reproduce his initial results. It is only recently that true disorder-to-order transitions have been reproducibly documented in clay systems [4]. The timespan between these studies and Langmuir’s initial investigations may be attributed to the inherent tendency for layered clays to form viscoelastic gels and/or glasses when mixed with water (a feature that industrially is heavily exploited when clays are used as e.g. rheology modifiers). Gelation or glassy behaviours are however in the context of liquid crystals traditionally viewed as disadvantageous, because gelled and/or glassy systems are in a non-ergodic, out-of-equilibrium state [5] so that phase transitions at thermodynamic equilibrium cannot be observed.Our studies do however show that high degrees of orientational order can be promoted also in strongly viscoelastic aqueous dispersions of Laponite RD (a commerical synthetic plate-shaped hectorite clay) and in aged and/or gelled dispersions of Na-fluorohectorite (a synthetic plate-shaped fluorohectorite). We document the presence of such order through crossed-polarizers photography, Mueller Matrix ellipsometry and small- and wide-angle x-ray scattering (SAXS and WAXS), and characterize the order quantitatively by calculating nematic order parameters based on WAXS data [6]. Because the types of clays used in this study are comercially important, and also representative pure-phase models of natural Mg-smectites, we argue that the ability to promote orientational ordering also in aqueous out-of-equilibrium clay gels and/or glasses could have implications for studies in which nanoplatelets of clays feature as structural modifiers (e.g. in clay-polymer hydrogels) or as transport-barriers (e.g. in papers and/or plastics containing clays).
9:00 PM - EE9.11
Synthesis and Characterization of Indium Oxide Doped Hematite Solid Solution Nanoparticles.
Monica Sorescu 1 , Tianhong Xu 1 , Lucian Diamandescu 2
1 Physics, Duquesne University, Pittsburgh, Pennsylvania, United States, 2 , National Institute of Materials Physics, Bucharest Romania
Show AbstractIndium oxide-doped hematite xIn2O3*(1-x)alpha-Fe2O3 (x= 0.1-0.7) ceramic solid solution systems were synthesized using mechanochemical activation by ball milling and characterized by XRD, Mössbauer spectroscopy, SEM, and simultaneous DSC-TGA. The microstructures and magnetic phases of as obtained solid solutions were dependent on the starting molar concentration x of In2O3 and the ball milling time. XRD patterns yielded the dependence of lattice parameters and particle sizes as a function of ball milling time. After 12 h ball milling, the completion of In3+ substitution of Fe3+ in hematite lattice occurs for x = 0.1, indicating that the solubility of In2O3 in hematite lattice is extended beyond the classical limits. For x = 0.3, 0.5 and 0.7, the substitutions between In3+ and Fe3+ into hematite and In2O3 lattice, respectively, occur simultaneously. The lattice parameters a and c of hematite and indium oxide extracted from Rietveld structural refinement vary as a function of ball milling time. The changes in these parameters were due to the ionic substitutions between In3+and Fe3+as well as the decrease in the particle sizes of indium oxide and hematite particles. The XRD peaks were broadened due to the formation of nanoparticles after long ball milling time. Mössbauer results showed: (1) at small molar concentration of x = 0.1, In3+ substitution of Fe3+ in hematite lattice occurs after milling and no Fe3+ substitution of In3+ in In2O3 lattice was observed. (2) at higher molar concentration of x = 0.3, 0.5 and 0.7, the substitutions between In3+ and Fe3+ into hematite and In2O3 lattice occur simultaneously and these two different substitutions were affected by the ball milling time. For x = 0.3, ball milling caused Fe3+ substitution of In3+ at D and B sites in In2O3 lattice, while for x = 0.5 and 0.7, only one doublet was observed, due to the high molar concentration of In2O3. SEM results showed the as-obtained solid solution ceramic system contains particles with a wide range of diameters, from micrometer to nanometer, but with a uniform distribution of O, Fe, and In elements by the EDS analysis. The formation of micrometer sized particles is due to the agglomerates, which contain the nano-sized grains. Two exothermic peaks on DSC curves of In2O3 indicated crystallization upon heating. Hematite partially decomposed upon heating. Ball milling has a strong effect on the thermal behavior of the as-obtained ceramic system. The hematite decomposition is enhanced due to the smaller particle size after ball milling. However, the weight loss of hematite decomposition decreases as a function of ball milling time, due to the gradual In3+-Fe3+ substitution in the hematite/indium oxide lattices. The crystallization of hematite and indium oxide was suppressed, with a drop of the enthalpy values and extensions to higher temperature values of exothermic peaks, due to the stronger solid-solid interactions during ball milling.
9:00 PM - EE9.12
Synthesis and Characterization of Indium Doped Gallium Oxide Nano- and Microstructures.
Antonio Utrilla 1 , Emilio Nogales 1 , Bianchi Mendez 1 , Javier Piqueras 1
1 Fisica de Materiales, Universidad Complutense de Madrid, Madrid Spain
Show AbstractTransparent conductive oxides (TCOs) are an attractive family of advanced functional materials of interest in a wide field of applications, from gas sensing to transparent thin film transistors (TFTs). The electrical conductivity in most of semiconductor oxides comes from the presence of oxygen vacancies, which act as donor centers. Recent works on transparent electronics include indium gallium oxide films as active channel material and the layer growth conditions are critical for the final device performance. For example, it has been demonstrated that a decrease of the oxygen partial pressure during the device preparation leads to an increase in the channel mobility. Also, the Indium concentration in the channel influences the mobility and the turn on voltage of the TFT transistors [1]. Therefore, a deep study of the role of indium, defects structure, oxygen vacancies and stoichiometry in indium gallium oxide microstructures is needed to elucidate the mechanisms responsible for the performance improvement in TFT devices. In this work, the incorporation of indium in gallium oxide microstructures and the relationship between chemical composition, morphology and optical properties have been investigated. Indium doped Ga2O3 nanowires and microstructures have been obtained by the controlled thermal annealing of metallic gallium in the presence of indium oxide powders under an argon flow. Novel morphologies for gallium oxide, such as helix microstructures, were obtained as a consequence of indium addition, along with other planar microstructures as in the case of undoped gallium oxide [2]. The investigation of the properties of the obtained microstructures has been carried out by means of X ray diffraction, scanning and transmission electron microscopy, cathodoluminescence in the SEM, X-ray energy dispersive spectroscopy (EDS) and spatially resolved X ray photoelectron spectroscopy (XPS). Indium atoms may incorporate into the gallium oxide lattice occupying the Ga sites and become electrically active, or may form complex with structural defects and then become electrically inactive. On the other hand, the possible formation of indium oxide clusters cannot be ruled out. The high spatial resolution of the employed techniques (XPS, CL and X-ray microanalysis in the SEM) has enabled us to investigate the defects structure and the indium homogeneity in the microstructures. EDS results show that the In concentration is not homogeneous in the microstructures. XPS results indicate the presence of indium oxide along with indium doped gallium oxide and CL results reveals spatial variations in the defect related luminescence bands. In the light of these characterization results the properties of the structures will be discussed.References:[1] H. Q.Chiang et al. J. Vac. Sci. Technol. B. 24, 2702 (2006).[2] E. Nogales et al. Nanotechnology, 11, 115201 (2009).
9:00 PM - EE9.14
Tailoring the Formation of Cobalt Oxide Nanomaterials: From the Synthesis to the Photocatalytic H2 Production.
Davide Barreca 1 , Paolo Fornasiero 2 , Alberto Gasparotto 3 , Valentina Gombac 2 , Oleg Lebedev 4 , Chiara Maccato 3 , Eugenio Tondello 3 , Gustaaf Van Tendeloo 5
1 Department of Chemistry - Padova University, CNR-ISTM and INSTM, Padova Italy, 2 Department of Chemistry, ICCOM-CNR Trieste Research Unit and INSTM - Trieste University, Trieste Italy, 3 Department of Chemistry, Padova University and INSTM, Padova Italy, 4 Laboratoire CRISMAT, ENSICAEN, CNRS, Caen Cedex France, 5 Electron Microscopy for Materials Science (EMAT), Antwerp University, Anwerpen Belgium
Show AbstractIn the last decade, cobalt oxides (CoO and Co3O4) have been the subject of various research activities in view of their potential use in several fields, from electrochemical devices to field emitters, from solid-state sensors to heterogeneous catalysts for environmental and energy-related applications. Nevertheless, only few reports are available on the use of cobalt oxide-based systems for the light-driven production of hydrogen, a very attractive energy vector, and none of these has ever focused on supported Co3O4 nanomaterials. Indeed, such systems might join the advantages of eliminating filtration processes required by powdered catalysts and the peculiar performances offered by nanostructured materials with tailored properties.In the present work our attention is devoted to an innovative Chemical Vapor Deposition synthesis of cobalt oxide nanomaterials. Specifically, depositions were carried out under dry O2 and O2 + H2O atmospheres on Si(100) substrates at temperatures between 300 and 550°C, with particular attention to the nucleation and growth processes of CoO/Co3O4 as a function of the adopted experimental conditions. The interrelations between the preparative conditions and the system composition, nanostructure and morphology were investigated by means of complementary characterization techniques. As a general rule, the selective formation of Co3O4 was favoured by an increased growth temperature and total pressure (from 3.0 to 10.0 mbar). In the latter case, single-phase Co3O4 nanostructures were synthesized at 550°C and in O2 + H2O atmospheres. Water vapor had a peculiar influence on the system morphology, producing highly crystalline Co3O4 nanoaggregates with a pronounced pyramidal faceting. Conversely, less oxidative conditions (3.0 mbar) enabled the obtainment of CoO nanosystems, whose morphology directly depended on the deposition temperature.The obtained materials were tested for the first time in the photo-assisted H2 production from methanol/water media, yielding a remarkably stable hydrogen evolution rate over significant periods of time. The present findings pave the way to the development of mixed cobalt oxide-containing nanocomposites for further advancements in photo-assisted hydrogen generation, with particular attention on the selectivity towards H2 obtainment at expenses of carbon-containing gaseous by-products. The engineering of the present nanosystems as multi-functional catalytic platforms for both hydrogen generation and oxygen activation will also be the object of future studies.
9:00 PM - EE9.15
Structural Diversity and Magnetic Properties of a Series of Complexes Based on Divalent Nickel and Linear Dicarboxylate Linkers.
Marlon Conato 1 , Xiqu Wang 1 , Ming Liu 2 , Chunrui Ma 2 , Chonglin Chen 2 , Allan Jacobson 1
1 Chemistry, University of Houston, Houston, Texas, United States, 2 Physics, University of Texas at San Antonio, San Antonio, Texas, United States
Show AbstractA series of coordination polymers, showing a variety of 2D and 3D architectures, based on dicarboxylate-bridged nickel(II) octahedra were prepared by solvothermal process and evaluated for magnetic properties. Two compounds with layered structures, Ni3(1,4-BDC)3(DMF)2(DMA)2 (1a) and Ni3(1,4-BDC)3(DMF)4 (1b) [1,4-BDC= terephthalate, DMF= N,N’-dimethylformamide, and DMA= dimethylamine] have been produced depending upon the extent of hydrolysis of the solvent, DMF. Framework compounds, Ni3(2,6-NDC)3(DMF)2(DMA)2 (2) and Ni(μ3-O)(4,4’-BPDC)3(DMA)3 (3) [2,6-NDC= naphthalate and 4,4’-BPDC= 4,4’-biphenyldicarboxylate] showed two different nickel-trimer configurations due to a slight variation in length of the dicarboxylate linkers. Another three dimensional compound based on an unprecedented nickel-tetramer building unit, Ni4(μ3-O)(1,4-NDC)4(DMF)2(DMA)2 (4) [1,4-NDC= 1,4-naphthalenedicarboxylate] has been obtained by using dicarboxylate linker with an added functionality. The compounds displayed diversity not only in structures but also in their magnetic characteristics.
9:00 PM - EE9.16
Periodically Ordered Mesoporous Co3O4/Heteropoly Acid Composite Frameworks for Catalytic Applications.
Gerasimos Armatas 1
1 Materials Science and Technology, University of Crete, Heraklion, Crete, Greece
Show AbstractMesoporous composite frameworks of transition-metal oxides (e.g. Co3O4, Fe2O3, Cr2O3, CeO2) with large internal surface area and uniform pores are impacting a diverse set of technological fields, including catalysis, magnetism and chemical sensing. These materials can combine complementary functionalities into the inorganic structure such as regular nanoporosity and high catalytic activity. An extension to synthetic strategies for advanced materials with desired emergent properties involves assembly of multi-functional nanostructures by using pre-organized nanocomposites or nanoclusters, such as the metal-oxide compounds and polyoxometalates. The polyoxometalates of the early transition metals (V, Nb, Mo, Ta, W) are an interesting subclass of anionic metal-oxygen compounds with fascinating properties, especially those in redox- and photo-catalysis. The plethora of structural and compositional types in these clusters makes them suitable building blocks for the construction of novel materials with specific functionalities. Cobalt oxide (Co3O4) is an important material with useful technological applications in redox catalysis, magnetism and energy storage. Nanostructured arrays of Co3O4 with ordered mesostructure and high surface area may exhibit unusual properties such as quantum confinement and improved electron transfer and magnetic interactions. It is expected that coupling of these functional components into a mesoporous structure can provide complementary or enhanced physicochemical properties in the former. Herein we report on the synthesis of periodically ordered mesoporous frameworks consisting of cobalt oxide and tungstophosphoric acid (H3PW12O40, hereafter HPW) components through a hard-templating method. The mesoporous framework of these materials constituted by nanocrystalline Co3O4 and HPW clusters in different composition (6-36 wt.% in HPW). Small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM) and nitrogen physisorption measurements indicate a well-ordered mesostructure in three-dimensional cubic symmetry. Also, the Keggin structure of the incorporated {PW12O40}3- anions into the composite frameworks was confirmed with X-rays diffuse scattering and pair distribution functional analysis (PDF) and UV/vis spectroscopy. Preliminary catalytic studies showed that these mesoporous Co3O4/HPW composites decompose the N2O into N2 and O2 with exceptional activity. We believe that these mesoporous composites are expected to have great implication in various fields of catalysis, including combustion of pollutants and partial oxidation of hydrocarbons.
9:00 PM - EE9.17
Solid-state NMR Studies of NaAlH4-based Hydrogen Storage Materials.
Margriet Verkuijlen 1 , Jinbao Gao 2 , Petra de Jongh 2 , Wiebke Lohstroh 3 , Maximilian Fichtner 3 , Ernst van Eck 1 , Jan van Bentum 1 , Arno Kentgens 1
1 Institute for Molecules and Materials, Radboud University, Nijmegen Netherlands, 2 Inorganic Chemistry and Catalysis, Utrecht University , Utrecht Netherlands, 3 Institute of Nanotechnology, KIT, Karlsruhe Germany
Show AbstractOne of the main issues to be solved for a hydrogen-driven economy is H2 storage for mobile applications. A promising method is the use of complex metal hydrides. The model compound NaAlH4 combines relatively high gravimetric hydrogen content with suitable thermodynamical properties. The release/absorption and reversibility in NaAlH4 is greatly enhanced by Ti doping or nano-confinement of the material. However, no detailed insight in the exact catalytic effect exists. Solid-state NMR is a versatile tool to study the structural and dynamical properties of these materials. 1H, 27Al and 23Na are easy accessible nuclei, atomic motions can be studied and no long-range crystalline order is required. NMR spectra of NaAlH4 indicate a rigid crystal lattice because no motional averaging of the dipolar couplings is present. For pure Na3AlH6, narrowed spectra are observed, which broaden at lower temperatures. This effect is successfully described by thermally activated rotational jumps of AlH6 clusters. Remarkably, even at cryogenic temperatures of 5 K, for Na3AlH6 no rigid crystal lattice is observed. An unfavourable property of the sodium alanates is that they react violently with O2 and H2O. Because of safety issues and to maintain long term storage capacity, it is important to get insight in this oxidation process. Double resonance and MQMAS NMR experiments show the formation of an intermediate phase, which consists of a sodium aluminium hydroxide with Al in tetrahedral hydroxide coordination. The final products mainly consist of aluminium hydroxide, with octahedrally coordinated aluminium, and sodium hydroxide. The structural properties of NaAlH4/C nanocomposites, synthesized by melt infiltration on a highly porous carbon support, were studied by 27Al and 23Na solid-state NMR. After melt infiltration, the local structure of NaAlH4 is preserved because a comparable chemical shift and average quadrupolar coupling constant as in bulk NaAlH4 is found. The spectra are mainly broadened because of a distribution in chemical shifts indicating a larger disorder in the material. In partly decomposed samples, no Na3AlH6 is detected. Together with a single release peak observed by dehydrogenation experiments, this points towards decomposition in one single step, in contrast to bulk alanates. The observed structural properties are restored after one rehydrogenation cycle. This demonstrates that the dehydrogenation of the NaAlH4/C nanocomposite is reversible, even without a Ti-based catalyst.
9:00 PM - EE9.18
In-situ Correlation of Nonstoichiometry and Materials Properties: High-temperature Study Using Cerium Oxide.
Denny Richter 1 , Han Xia 1 , Silja Schmidtchen 1 , Holger Fritze 1
1 , TU Clausthal, Goslar Germany
Show AbstractAdvanced materials for e.g. high-temperature fuel cells or solid-state sensors exhibit some nonstoichiometry due to intentional doping or operation in harsh environments. Therefore, tailoring of these materials requires a detailed knowledge about the correlation of nonstoichiometry and materials properties of great technological importance such as conductivity, expansion and phase stability. So far, the determination of the nonstoichiometry at high-temperatures is quite complex and hardly accompanied by in-situ methods which prevent reliable correlations with the above mentioned properties of interest.This study presents a new characterization method based on high-temperature stable piezoelectric resonators. Such transducers consist of a single crystalline langasite plate (La3Ga5SiO14) and platinum electrodes which enables the excitation of bulk acoustic waves up to at least 1000°C. The materials of interest are deposited in form of thin films either on one or both sides of the resonators. The key feature of the approach is the detailed analysis of the resonance spectra for the arrangements resonator/film and film/resonator/film using a one-dimensional physical model. Thereby, the impact of mechanical stress can be discriminated which enables in the extraction of the materials properties of interest. Precondition is the detailed knowledge of the materials properties of the langasite transducer. The in-situ characterization results simultaneously in information about nonstoichiometry, expansion and conductivity. The investigations are accompanied by impedance spectroscopy and ex-situ methods such as XPS and AES to determine the stoichiometry and the valence state of the materials of interest independently.Cerium oxide (CeO2-x) is chosen as a model material since it shows high oxygen nonstoichiometry as a function of the oxygen partial pressure. About 5 µm thick films are deposited on the piezoelectric resonators by laser ablation. The resonance spectra are acquired in the temperature range from 600 to 800°C at oxygen partial pressures from 0.2 to 10^-25 bar. Below 10^-20 bar, changes in the resonance frequency by several 10 Hz could be attributed to mass changes, i.e. to changes in stoichiometry. The data correspond to those shown in Ce-O phase diagrams and are in general accordance with the conductivity as determined by impedance spectroscopy. Simultaneously, low oxygen partial pressures cause increased damping of the resonance spectra. The effect is described by changes in the effective viscosity of cerium oxide.In summary, a method is presented which shows the potential to correlate nonstoichiometry and other materials properties of a wide variety of oxides at high temperatures in an effective and precise manner.
9:00 PM - EE9.19
Preparation of Protonated Titanate Nanotube Films with an Extremely Large Wetting Contrast.
Yuekun Lai 1 2 , Yuxin Tang 1 , Dangguo Gong 1 , Changjian Lin 2 , Zhong Chen 1
1 School of Materials Science and Engineering, Nanyang Technological University, Singapore Singapore, 2 College of Chemistry and Chemical Engineering , Xiamen University, Xiamen China
Show AbstractSince Kasuga et al. reported the fabrication of protonated titanate nanotubes (TNTs) by hydrothermal process at 1998 [1], TNTs had attracted tremendous interest due to its large specific surface area, excellent ion-exchange and intercalation activities. It can be used as adsorbants, deodorants, and functional nanoparticle carriers [2,3]. However, the poor dispersion of TNTs in aqueous or organic matrix greatly blocks the fabrication of uniform TNT film. Therefore, it remains a great challenge to develop a method to effectively prepare uniform TNT film with good adhesion. In this work, we developed a tetrabutylammonium ion functionalization process to obtain a stable and dispersed electrolyte containing titanate nanotubular particles that were synthesized by a hydrothermal approach. A facile electrophoretic deposition (EPD) process has been applied to prepare uniform and compact films consisting of titanate nanotubes. Such an EPD process offers easy control in the film thickness and the adhesion to the substrate was found to be strong. It was found that the functionalization of TNTs plays a key role on the electrolyte stability and the formation of a uniform TNT film with good adhesion. The water droplet spreads quickly to a contact angle of around 6° within 0.02 s, and completely wetted the titanate porous film within 0.16 s. This result indicates the as-prepared film deposited by EPD is superhydrophilic without any UV irradiation (unlike TiO2). However, the contact angle of the corresponding nanostructured film was changed greatly from nearly 0° to 152.3° after soaking in 1H,1H,2H,2H-perfluorooctyl-triethoxysilane (PTES) solution [4,5]. The bead was firmly adhered to the surface when the TNT sample was tilted to a vertical position, or even when turned upside down. This study provides an interesting method to prepare films with extremely high wettability contrast that are useful for producing different types of functional materials. References[1] T. Kasuga, M. Hiramatsu, A. Hoson, T. Sekino, K. Niihara, Langmuir 14 (1998) 3160.[2] Y.K. Lai, Y.C. Chen, H.F. Zhuang, C.J. Lin, Mater. Lett. 62 (2008) 3688.[3] Y.X. Tang, Y.K. Lai, D.G. Gong, K.H. Goh, T.T. Lim, Z.L. Dong, Z. Chen, Chem. Eur. J. DOI:10.1002/chem.201000330.[4] Y.K. Lai, C.J. Lin, J.Y. Huang, H.F. Zhuang, L. Sun, T. Nguyen, Langmuir 24 (2008) 3867.[5] Y.K. Lai, X.F. Gao, H.F. Zhuang, J.Y. Huang, C.J. Lin, L. Jiang, Adv. Mater. 21 (2009) 3799.
9:00 PM - EE9.2
Monosteps on Mesostructured Silica and Titania Thin Films and Room-temperature Phosphorescence from Mesoporous Silica.
Lei Zhao 1 , Tian Ming 1 , Jianfang Wang 1
1 Department of Physics, The Chinese University of Hong Kong, Hong Kong China
Show AbstractTwo new phenomena on mesostructured and mesoporous materials have been observed and studied. First, steps are observed on the surfaces of mesostructured silica and titania thin films that are several-mesostructural-layer thick (Small 2010, accepted). The heights of the steps are found to correspond to only one layer. These monosteps form circular rings on the film surface. The formation of the monosteps involves the cooperative interaction between the organic and inorganic components. The formation of monosteps on mesostructured thin films will have important implications for the use of such materials in low-dielectric-constant applications and for developing high-performance thin film-based sensing devices. Second, room-temperature phosphorescence from metal-activator-free mesoporous silica has been discovered and investigated (work submitted). The light emission is strong and can persist for seconds after removing the excitation light. Both photoluminescence and phosphorescence spectra contain several peaks in the visible range. Carbon atom substitutions for the silicon atoms in the O-Si-O networks are believed to be the luminescence centers. Phosphorescent monoliths have been further fabricated. Their shapes and sizes can be readily controlled. This mesoporous silica can not only be used as a low-density, environmentally friendly phosphor for lighting and display applications, but also serve as a nontoxic and optically detectable carrier for drug delivery.
9:00 PM - EE9.20
Sintering Behavior of Ce0.9Gd0.1O1.95-δ Electrolyte in a Reducing Atmosphere.
Zeming He 1 , Vincenzo Esposito 1 , Andreas Kaiser 1 , Severine Ramousse 1
1 Fuel Cell and Solid State Chemistry, Technical University of Denmark, Roskilde Denmark
Show AbstractAs solid dense electrolyte, cerium gadolinium oxide is one of the excellent candidates in the applications of solid oxide fuel cells and oxygen sensors. In the present work, Ce0.9Gd0.1O1.95-δ (CGO10) compacts were studied under different oxygen partial pressures using dilatometry, thermogravimetry and gradient sintering techniques. The defect chemistry and the sintering constitutive laws were employed to evaluate and determine the key parameters related to sintering, such as relative density, densification rate and activation energy for densification, from the experimental results. The effects of initial particle size, green density and oxygen partial pressure on sintering evolution of CGO10 are investigated. Compared to that of in air, accelerated densification was observed in early-stage sintering of CGO10 in H2/N2 at lower sintering temperature (1000 oC). This might be attributed to the oxygen vacancies generated by the reduction of Ce4+ to Ce3+ in reducing atmosphere, which facilitate the diffusion of ions through the lattice. From this promising fact, the sintering processes of CGO10 were further optimized by choosing starting particle size and density and controlling sintering atmospheres, in an attempt to achieve dense CGO10 at relatively low sintering temperatures.
9:00 PM - EE9.21
Single Layer Reduced Graphene Oxide-periodic Mesoporous Silica Sandwich Nanocomposites with Vertically Oriented Channels.
Zheng-Ming Wang 1 2 , Wendong Wang 1 , Neil Coombs 1 , Geoffrey Ozin 1
1 Chemistry, University of Toronto, Toronto, Ontario, Canada, 2 Energy Technology Research Institute, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki, Japan
Show AbstractThis paper describes the synthesis and characterization of single layer graphene oxide-periodic mesoporous silica sandwich nanocomposites denoted GO-PMS. Through a comprehensive exploration of the synthesis conditions it has proven possible to create the first example of a graphene oxide-PMS nanocomposite in which hexagonal symmetry PMS film grows on both sides of the graphene oxide sheets with the mesoporous channels vertically aligned with respect to the graphene surface. The formation of this novel architecture is found to be very sensitive to pH, the ratio of surfactant template to graphene oxide, the amount of silica precursor, and the temperature of the synthesis. Based on the collected data it is proposed that the mode of formation of the nanocomposite involves the co-assembly of silicate-surfactant admicelles on opposite sides of reduced graphene oxide platelets acting thereby as a template for growth of vertical mesopores off the platelet surface.
9:00 PM - EE9.22
Controlled Synthesis of Cobalt Phosphide Hyperbranched Nanocrystals Using TOPO as Phosphorus Source.
Haitao Zhang 1 , Don-Hyung Ha 1 , Richard Robinson 1
1 Materials Science and Engineering, Cornell University, Ithaca , New York, United States
Show AbstractThe novel hyperbranched Co2P nanocrystals have been synthesized via a simple colloidal solution method by using TOPO as a phosphorus source. Reaction mechanism studies show that Co metal is an intermediate for the formation of Co2P and TOPO could be a general useful phosphorus source for the synthesis of other metal phosphides. By varying the synthetic parameters, the morphologies of the hyperbranched nanocrystals can be controlled from simple two-arm bundles (81 ± 4 nm, the length of each arm) to hexagonal symmetric six-arm structure (360 ± 30 nm). The SEM and 3-D electron tomography study have shown that each arm has a three-dimensional cylindrical shape, while most of the multiple-arm particles display planar structures. The hyperbranched structures may form by the crystal splitting, and the presence of the excess neutral acid was found to be important in this process. The formation of symmetric six-arm structure was attributed to the orthorhombic cyclic twining, and the dark field TEM results proved that each opposing arm grows from the same seed crystal. This growth mechanism study provided a useful tool for further understanding the complex nanoparticle morphology evolution.
9:00 PM - EE9.25
Role of Native Defects in the Dehydrogenation of Lithium Alanate.
Khang Hoang 1 , Chris Van de Walle 1
1 Materials Department, University of California, Santa Barbara, California, United States
Show AbstractLithium alanate (LiAlH4) is a potential material for hydrogen storage due to its high hydrogen density. It is well established that hydrogen desorbs from LiAlH4 in a three-step decomposition similar to that of the widely studied NaAlH4. However, the fundamental mechanisms behind the decomposition and (de)hydrogenation processes in this material are not fully understood, and we expect that once such understanding has been established, one can envisage a solution for improving the material’s performance. Experimental data suggest that the dehydrogenation of LiAlH4 involves mass transport by point defects. This motivates us to perform first-principles calculations based on density functional theory for native point defects and defect complexes in LiAlH4. In this talk, we propose specific mechanisms for the decomposition and dehydrogenation of LiAlH4 based on our understanding of the structure, energetics, and migration of Li-, Al-, and H-related defects.
9:00 PM - EE9.27
Crystallization of the Energetic Materials RDX and HMX: Morphology and Structure Properties.
Ilana Goldberg 1 , Jennifer Swift 1
1 Department of Chemistry, Georgetown University, Washington, District of Columbia, United States
Show AbstractThe performance of energetic materials RDX and HMX depend on a variety of crystalline properties including material phase, solubility, density and defect structures. Though widely studied for many years, a detailed understanding of how the growth environment affects the molecular properties of these compounds remains incomplete. In this work, RDX and HMX were crystallized from a variety of different solvents and on 2D self-assembled monolayer (SAM) templates. Crystals were analyzed using Raman spectroscopy and X-ray diffraction techniques in order to assess the crystal phase, orientation and defect structure. Concomitant polymorphism was observed for both RDX and HMX under certain growth conditions, with preferred orientations and phases adopted on SAM templates. Understanding the intimate relationship between the growth conditions and the resultant properties of the crystalline phases obtained is an important prerequisite to improving the performance of these materials when used in plastic bonded explosives.
9:00 PM - EE9.28
Production of Core-shell Type FTO/TiO2 Nanoparticles for Dye Sensitized Solar Cells.
Kerem Icli 2 , Ahmet Ozenbas 1 2
2 Micro and Nanotechnology Graduate Program, Middle East Technical University, Ankara Turkey, 1 Metallurgical and Materials Engineering, Middle East Technical University, Ankara Turkey
Show AbstractDye sensitized solar cells (DSSC) employing nanoparticle based mesoporous anodes have been extensively studied in the recent years. Although best efficiencies are obtained with cells made from titanium dioxide (TiO2), application of new metal oxides and anode structures is a major subject of research. Tin dioxide (SnO2) is a promising candidate presenting high electron mobilities and electronic conductivity upon doping with elements like fluorine. In this work, as a novel production technique, homogeneously precipitated tin dioxide nanoparticles has been doped with fluorine under hydrothermal conditions resulting in resistivies around 770 ohm.cm. Dye sensitized solar cells have been constructed by screen printing from bare fluorine doped SnO2 nanoparticles (FTO), commercial TiO2 nanoparticles and core shell type mesoporous anodes employing TiO2 as shell material. TiO2 coating has been achieved from hydrolysis of aqueous solutions of ammonium hexafluorotitanate and titanium tetrachloride as precursor materials. Upon surface treatment of tin dioxide, photovoltage, photocurrent and fill factor of cells have been extensively improved as a result of supression of recombination reactions. Best results were obtained from titanium tetrachloride treated cells giving current densities of 22.8 mA/cm2, higher than TiO2, however photovoltage and fill factor are still lower than TiO2, giving efficiencies of 4.61% and 6.54%, respectively.
9:00 PM - EE9.29
Nanosize Effects on the Conduction Properties in Nanocrystalline SrTiO3: Charge Carrier Chemistry as a Function of Oxygen Partial Pressure.
Piero Lupetin 1 , Giuliano Gregori 1 , Joachim Maier 1
1 , Max Planck Institute for Solid State Research, Stuttgart Germany
Show AbstractDefect chemistry is the key to the understanding of ionic and electronic transport properties of solids. Notably, the study of ionic and electronic transport properties of nanosized objects has become crucial, since their electrical conductivity properties may drastically change due to the fact that boundaries properties become predominant over the bulk properties. The basis for the understanding of such effects is provided by the field of nanoionics, which allows the elucidation of defect chemistry not only for well-separated boundary zones but also in the more exciting mesoscopic range where the distance of the interfaces (grain size) is on the order or below the characteristic decay length of a semi-infinite interface.In the present contribution, we investigated SrTiO3, which is an excellent model material for electroceramic oxides, thanks to its pronounced stability and its well explored defect chemistry. The oxygen non-stoichiometry plays a crucial role in determining whether this perovskite is p-type, n-type or ionic conductor or even a superconductor. Therefore, the oxygen non-stoichiometry is a key element for applications such as superconducting devices, fuel cell electrodes, solid electrolytes or dielectrics and it can be tuned by variation of the oxygen partial pressure under equilibrium conditions.Here, the conductivity properties of nanocrystalline SrTiO3 (grain size lower than 50 nm) have been investigated over a broad range of oxygen partial pressures. In this material, no bulk unperturbed by interfacial zones is present and the overall electrical properties are clearly dominated by the grain boundaries. Notably, the stoichiometry variation of the mesoscopic situation, in which the space charge zones overlap, reveals several exciting size-induced phenomena: increase of n-type conductivity by several orders of magnitude, an equally great depression of p-type conductivity and an even stronger depression of oxygen vacancy conductivity when compared to the macroscopic situation. The most striking phenomenon is the giant shift of the p/n transition by 12 orders of magnitude in terms of partial pressure. The results can be explained in the light of space charge effects occurring as a consequence of a positive excess charge in the grain boundary core.
9:00 PM - EE9.3
The Electronic Structure of Crystalline and Amorphous Bismuth.
Zaahel Mata-Pinzon 1 , Renela Valladares 2 , Alexander Valladares 2 , Ariel A. Valladares 1
1 Condensed Matter, Instituto de Investigaciones en Materiales, UNAM, Mexico, D.F. Mexico, 2 Physics, Facultad de Ciencias, UNAM, Mexico, D.F. Mexico
Show AbstractStarting with a crystalline 64-atom supercell of bismuth (Bi) we generate the corresponding amorphous structures, using the undermelt-quench approach [1] and a variant. In this work we concentrate on the electronic properties. We first characterize the amorphous phases by determining the radial distribution functions, next we calculate the electron density of states (eDOS) of the crystalline structure (x-Bi) and of two amorphous phases. To do this we use a code based on the Density Functional (DF) method and the Local Density Approximation (LDA). To generate the amorphous topology we heat the sample linearly to a temperature just below the melting temperature of x-Bi and then two paths are followed: i) in the undermelt approach, the sample is cooled to 0 K; ii) the other path is to heat the sample to just above the melting temperature, maintaining it for 100 computational steps and then cooling it down to 0 K in one step. The amorphous structures found at the end of the two paths are similar. The calculated eDOS for the crystalline structure is compared to other results obtained by different computational techniques and experiments and the agreement is good in both cases. This is done to validate our approach before applying it to the amorphous structures for which there are no simulational or experimental results. Our results indicate that the amorphized samples have more than 4 times the density of states of crystalline Bi at the Fermi level, thus explaining why amorphous Bi is more a metal than x-Bi. This may be relevant to explain the superconductivity of amorphous Bi and the non-superconductivity of x-Bi. [1] A new approach to the ab initio generation of amorphous semiconducting structures. Electronic and vibrational studies, Ariel A. Valladares, (Chapter 3) in: Glass Materials Research Progress, Editors: Jonas C. Wolf and Luka Lange, pp. 61-124 © 2008 Nova Science Publishers, Inc. ISBN 978-1-60456-578-2.
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Intercalated Water in Synthetic Lithium-fluorhectorite Clay.
Romulo Tenorio 1 , Mario Engelsberg 2 , Jon Fossum 3 , Geraldo da Silva 4
1 Programa de Pos-Graduao em Ciencia de Materiais, Universidade Federal de Pernambuco (UFPE), Recife, PE, Brazil, 2 Departamento de Fisica, Universidade Federal de Pernambuco (UFPE), Recife, PE, Brazil, 3 Department of Physics, Norwegian University of Science and Technology (NTNU), Trondheim Norway, 4 Departamento de Fisica, Universidade de Brasilia (UnB), Brasilia, DF, Brazil
Show Abstract7Li and 1H nuclear magnetic resonance together with X-ray diffraction measurements in powdered samples and pseudocrystalline films of synthetic Li-fluorhectorite as a function of relative ambient humidity permit to address several aspects of the structure and dynamics of intercalated water molecules. The role of proton exchange as a possibly dominant mechanism of charge transport in the one-water layer regime of hydration is reexamined. The experimental results in Li-fluorhectorite support the result of molecular simulations which predict, for Li-montmorillonite, the existence of an intermediate regime, between one-water layer and two-water layer states.References:[1] Intercalated Water in Synthetic Fluorhectorite Clay, Romulo P. Tenorio, M. Engelsberg, Jon Otto Fossum and Geraldo J. da Silva, Langmuir 26, 9703–9709 (2010);[2] Geometry and Dynamics of Intercalated Water in Na-Fluorhectorite Clay, Hydrates, Romulo Tenorio, Lars Alme, Mario Engelsberg, Jon Otto Fossum and Fernando Hallwass, J.Phys.Chem.C, 112,575-580 (2008)
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Mechanistic Insights into Nucleation and Growth of Molybdenum Dioxide Nanoparticles in Nonaqueous System and Their Electrochemical Properties.
Dorota Koziej 1 2 , Marta Rossel 2 , Bettina Ludi 2 , Andreas Hintennach 3 , Petr Novak 3 , Jan-Dierk Grunwaldt 4 , Markus Niederberger 2
1 , Harvard University, Cambridge, Massachusetts, United States, 2 Department of Materials, ETH Zurich, Zurich Switzerland, 3 Department of General Energy, Paul Scherrer Institut, Villigen Switzerland, 4 Institute for Chemical Technology and Catalysis, Karlsruhe Institute of Technology, Karlsruhe Germany
Show AbstractThe study of nanoparticles growth and assembly in nonaqueous synthesis have provided a tangible link between organic reaction and the properties of inorganic particles, but experiments have not yet explored the inorganic reaction ahead of the nucleation of nanoparticles. This fundamental issue points to the importance of in situ monitoring of not only the organic, but also the inorganic reaction pathway during the synthesis of nanoparticles. Here we present for the first time synthesis of MoO2 nanoparticles in nonaqueous medium and investigate the consecutive steps by means of complementary methods: in-situ EXAFS, XRD, SEM and TEM. The experiments show that the crystallization process of MoO2 nanoparticles is initiated by reduction of MoO2Cl2 precursor in benzyl alcohol and acetophenone at the molecular level. This reaction triggers the in situ formation of Mo(IV) monomer, leading to critical supersaturation and nucleation of spherical hexagonal MoO2 nanoparticles. We demonstrate that the reaction medium has a central role on the first step of crystallization of nanoparticles which is in our case Mo-O-Mo bonds formation from the in situ reduced precursor. Our results suggest that in pure acetophenone this reaction is an aldol condensation with release of HCl and 1,3,5-triphenylbenzene as a side product of MoO2 crystallization. Whereas when benzyl alcohol is present in the reaction medium, the chloride most probably attacks the carbonyl group of alkyl and BnCl is released. The results provide evidence that the spherical few nm large hexagonal particles subsequently aggregate into assemblies with the same crystallographic orientation, which in turn re-crystallize into monoclinic spheres and this spheres are the building blocks for nanorod formation. The growth control of anisotropic MoO2 nanoparticles can be understood in terms of an oriented attachment growth model under different kinetic conditions as determined by different acetophenone and benzyl alcohol concentrations. We observed two stages. In synthesis at low acetophenone concentration, the bimodal distribution of shape is observed. By contrast, in syntheses with high concentration of acetophenone foremost rod-like nanoparticles, or assemblies thereof are observed. Furthermore, we demonstrate how molybdenum dioxide nanoparticles are useful as electrodes in rechargeable batteries. These include the test of the electrochemical performance and in-situ XAS and XRD studies of their thermal stability. We suggest that the rode-like shape of molybdenum dioxide nanoparticles facilitates the excellent electrochemical cycling performance, namely long term stability and reversibility for lithium-ion insertions and de-insertions.
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Platinum Nanotubes Synthesized by Templated MOCVD.
Alexander Papandrew 1
1 Chemical and Biomolecular Engineering, University of Tennessee, Knoxville, Tennessee, United States
Show AbstractMetallic and metal oxide nanotubes have applications as catalysts, as electrode materials for electrochemical storage and conversion devices, and in sensors. Many of these nanostructures have been made by coating nanostructured templates through various means followed by subsequent etching or dissolution of the template.I will detail a simple templated synthesis route for platinum nanotubes based on metalorganic chemical vapor deposition of platinum on anodic alumina. While conventional CVD is predicated on reactant flow through a hot zone or upon a heated substrate, this work uses a unique CVD process absent of convective flow. The nanostructured coatings that result from the latter process are highly conformal and exhibit very high yield. The solid metalorganic precursor platinum 2,4-pentanedionate was placed in contact with a monolithic anodic alumina membrane in a vacuum oven and heat treated in an atmosphere of N2 and water vapor. The templates were then dissolved in a KOH solution and the remaining solids were collected for analysis. The resulting platinum nanotubes had a uniform 200 nm outer diameter and a wall thickness of up to 30 nm, dependent on the initial precursor loading The nanotubes were further analyzed by SEM, TEM, XRD, and XPS. Other prospective applications of the "no-flow" MOCVD technique will also be discussed.
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Structure-property Relationship of Metal-organic Frameworks (MOFs) and Physisorbed Off-gas Radionuclides.
Dorina Sava 1 , Terry Garino 2 , Karena Chapman 3 , Peter Chupas 3 , Tina Nenoff 1
1 Surface & Interface Sciences, Sandia National Laboratories, Albuquerque, New Mexico, United States, 2 Electronic & Nanostructured Materials, Sandia National Laboratories, Albuquerque, New Mexico, United States, 3 X-ray Science Division, Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractWe report on the host-guest interactions between metal-organic frameworks (MOFs) with various profiles and highly polarizable molecules (iodine), with emphasis on identifying preferential sorption sites in these systems.Radioactive iodine 129I, along with other volatile radionuclides (3H, 14C, Xe and Kr), represents a relevant component in the off-gas resulted during nuclear fuel reprocessing. Due to its very long half-life, 15.7×106 years, and potential health risks in humans, its efficient capture and long-term storage is of great importance. The leading iodine capture technology to date is based on trapping iodine in silver-exchanged mordenite. Our interests are directed towards improving existent capturing technologies, along with developing novel materials and alternative waste forms. Herein we report the first study that systematically monitors iodine loading onto MOFs, an emerging new class of porous solid-state materials. In this context, MOFs are of particular interest as: i) they serve as ideal high capacity storage media, ii) they hold potential for the selective adsorption from complex streams, due to their high versatility and tunability. This work highlights studies on both newly developed in our lab, and known highly porous MOFs that all possess distinct characteristics (specific surface area, pore volume, pore size, and dimension of the window access to the pore). The materials were loaded to saturation, where elemental iodine was introduced from solution, as well as from vapor phase. Uptakes in the range of ~125-150 wt% I2 sorbed were achieved, indicating that these materials outperform all other solid adsorbents to date in terms of overall capacity. Additionally, the loaded materials can be efficiently encapsulated in stable waste forms, including as low temperature sintering glasses. Ongoing studies are focused on gathering qualitative information with respect to localizing the physisorbed iodine molecules within the frameworks: X-ray single-crystal analyses, in conjunction with high pressure differential pair distribution function (d-PDF) studies aimed to identify preferential sites in the pores, and improve MOFs’ robustness. Furthermore, durability studies on the iodine loaded MOFs and subsequent waste forms include thermal analyses, SEM/EDS elemental mapping, and leach-durability testing. We anticipate for this in-depth analysis to further aid the design of advanced materials, capable to address major hallmarks: safe capture, stability and durability over extended timeframes. *Sandia National Laboratories is a multi-program laboratory operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin company, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.
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Scintillating Metal-organic-framework Materials for Radiation Detection: First Principles Calculations Towards Rational Design.
Alex Greaney 1 , Patrick Feng 2 , Mark Allendorf 2 , Jeffrey Grossman 1
1 Department of Materials Science and Engineering, Massechusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 , Sandia National Laboratory, Livermore, California, United States
Show AbstractMetal-organic-frameworks (MOFs) offer an exciting new class of scintillating materials for radiation detection. Using organic scintillating compounds as the linker molecules within the MOF architecture one can construct a range of new materials to systematically study the relationship between structure and optical properties. In this system the isoreticular MOFs IRMOF-9 and IRMOF-10 present a particularly interesting case study: Both are constructed from the same biphenyl dicarboxylic linkers strung between tetrahedral Zn$_4$O$^{+6}$ nodal clusters but have subtly different structures that give rise to very different optical properties. Here we present the results of density functional theory (DFT) calculations of these two systems directed at elucidating the origin of the differing optical properties.
9:00 PM - EE9.37
New Classes of Nanostructured Crystalline Materials.
Ngoc Nguyen 1 , Matthew Beekman 1 , Colby Heideman 1 , Mary Smeller 1 , Krista Hill 1 , Ryan Atkins 1 , David Johnson 1
1 Chemistry, University of Oregon, Eugene, Oregon, United States
Show AbstractAbilities to predict and to synthesize new crystalline solids compounds with targeted structures are two long-standing challenges in synthetic sold state chemistry, especially if they are not thermodynamically stable under accessible reaction conditions. The prediction of possible structures and relative stabilities of unknown compounds is hampered by the large phase space, as many elements are found in a variety of coordination geometries resulting in many potential packing arrangements, especially as the number of elements in prospective compounds increases. Local bonding rules are used to predict potential new compounds that will be kinetically stable, such as variants of a natural product that exhibits biological activity. The same principal of satisfying local bonding criteria potentially provides an avenue to predict kinetically stable extended crystalline solids. One potential class of kinetically stable extended crystalline compounds is nanolaminated solids, consisting of two or more constituents interwoven on a nanometer length scale. While one class of particularly ordered nanolaminated solids would be crystalline superlattices which have been prepared using molecular beam epitaxy and other epitaxial growth techniques, crystalline order between the constituents is not a prerequisite to kinetic stability. Non-epitaxial nanolaminates should be kinetically stable and display interesting properties as long as the interface between the constituents is kinetically stable and the defect densities at the interface do not dominate the physical properties one is looking to improve.Here we report the prediction and synthesis approach of new class of kinetically stable extended crystalline solids having two and three constituents based on modulated elemental reactant technique that contain the length scales of the desired products, taking advantage of slow solid-state diffusion rates. Details of experimental design and structure analysis of the new solids based on x-ray diffraction and transmission electron microscopy are discussed. Some physical properties are presented as well.
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Vertically Aligned ZnO/CeO2 Composite Nanorod Arrays and CeO2 Nanotube Arrays for Energy and Environmental Applications.
Gang Liu 1 , Pu-Xian Gao 1
1 Department of Chemical, Materials and Biomolecular Engineering, Institute of Materials Science, Storrs, Connecticut, United States
Show AbstractCerium dioxide (CeO2) is one of the most important rare-earth materials, which has diverse applications as solid electrolytes for solid oxide fuel cells, support components for three-way catalysts, catalysts for selective hydrogenation, abrasives for chemical polishing slurries and materials for ultraviolet blocking etc [1]. Recently, one-dimensional (1D) CeO2 nanostructures such as nanorods, nanowires and nanotubes have attracted extensive attention due to the improvements in the redox properties and transport properties with respect to CeO2 nanoparticles. Although random oriented 1D CeO2 nanostructures have been well developed, to the authors’ best knowledge, there is seldom report about the synthesis of vertically aligned 1D CeO2 arrays on substrates. The assembly of 1D CeO2 nanostructures into ordered three-dimensional (3D) nanostructures is very necessary for the development of high performance nanodevices. Zinc oxide (ZnO) is one of the few dominant nanomaterials for nanotechnology due to its wide applications in optics, optoelectronics, actuators, energy and biomedical sciences [2]. The synthesis of vertically aligned ZnO nanorods/nanowires arrays can be easily achieved by hydrothermal and vapor deposition methods [2]. In this work, utilizing hydrothermally grown ZnO nanorod arrays as templates, synthesis of ZnO/CeO2 core-shell composite nanorod arrays has been achieved via layer-by-layer (LBL) assembly [3], which is based on electrostatic attraction between positively charged Ce3+ ions and negatively charged ZnO nanorods. CeO2 nanotube arrays were also obtained by the dissolution of ZnO nanorod arrays. The synthesized ZnO/CeO2 composite nanorod and CeO2 nanotube arrays were characterized by a range of electron microscopy and spectroscopy. The resulting ZnO/CeO2 composite nanorod arrays and CeO2 nanotube arrays may find applications in the fields of energy and environmental catalysis, optoelectronics and more. Furthermore, it is expected that the preparation procedure could be applied for the synthesis of other well aligned composite nanorod and nanotube arrays.References[1]C. Tang, Y. Bando, B. Liu, D. Golberg, Adv. Mater. 2005, 17, 3005-3009.[2]Z.L. Wang, Mater. Sci. Eng., R 2009, 64, 33-71.[3]P. Wu, H. Zhang, N. Du, L. Ruan, D. Yang, J. Phys. Chem. C 2009, 113, 8147-8151.
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Factorial Analysis of the Water Splitting Activity of a Niobate Nanosheet Photocatalyst.
Erwin Sabio 1 , Nigel Browning 3 2 , Frank Osterloh 1
1 Department of Chemistry, University of California, Davis, Davis, California, United States, 3 Department of Chemical Engineering and Materials Science, University of California, Davis, Davis, California, United States, 2 Condensed Matter and Materials Division, Lawrence Livermore National Laboratory, Livermore, California, United States
Show AbstractTetrabutylammonium (TBA)-exfoliated nanosheets derived from the Dion-Jacobson phase KCa2Nb3O10 are known to catalyze photochemical water splitting under UV light. Here we present a systematic study into the effects of exfoliation, sacrificial charge donors, co-catalysts, and co-cocatalyst deposition conditions on the activity of this catalyst toward H2 and O2 production in aqueous media. Exfoliation into (TBA,H)Ca2Nb3O10 showed up to 15-fold increase in H2 evolution and an 8-fold increase in O2 evolution over the bulk phase under same conditions. H2 production improved by 2 - 3 orders of magnitude to (~20 - 30 mmol H2/hr/g) in the presence of sacrificial electron donor, methanol while O2 production up to ~400 μmol O2/hr/g is only observed in the presence of electron acceptor, AgNO3. Addition of co-catalysts Pt and IrOx increased H2 and O2 evolution rates, respectively. The presence or absence of sacrificial agents during co-catalyst photodeposition showed marked differences in H2 activity but not in O2 activity. Z-contrast high resolution scanning transmission microscopy (HR-STEM) and cyclic voltammetry were further used to elucidate structural and electronic band structure properties that account for the observed effects of the catalytic factors studied.
9:00 PM - EE9.41
Monitoring Sol-gel Synthesis of Colloidal Silica at Different Solvent Media.
Ozge Malay 1 , Yusuf Menceloglu 1
1 Materials Science and Engineering, Sabanci University, Istanbul Turkey
Show AbstractThe Stöber method is a well-known procedure for the sol-gel synthesis of monodisperse colloidal silica. Although this method has been widely investigated, there are very few studies on comprehensive understanding of the time-dependent growth mechanism of silica particles, but a generally accepted scheme has not been presented yet. The experimental procedure is very simple, but the underlying mechanism for the formation and growth of the charge-stabilized silica spheres are not. The standard procedure involves the base-catalyzed hydrolysis and condensation of silicon alkoxides in an alcohol-ammonia-water system. In this study, initially monodisperse approximately 50 nm silica nanoparticles were synthesized in a lower alcohol, ethanol, and the growth of the nanoparticles was monitored by dynamic light scattering (DLS), atomic force microscopy (AFM) and nuclear magnetic resonance techniques (NMR) up to five days. Conductivity of the reaction medium during growth was also displayed to follow the activity and mobility of the ionic species within this period. In the early stages of the synthesis, multi-modal distribution with variant shape was observed. Up to 6 hours, this multi-modal size distribution broadened and converted to a unimodal distribution with well-defined size and spherical shape. The colloidal stability could be attained after a certain radius is obtained, which is based on relative concentrations of TEOS, water and ammonia. Analyses show that initially formed polymeric structures collapses when they reach to a critical size, and after colloidal stability is obtained, it is preserved. Ongoing investigation focuses on this broadening effect and aims to characterize the size, distribution and colloidal stability of silica suspensions during growth by using a different alcohol as solvent (ethyl alcohol, isopropyl alcohol and tert-butyl alcohol). The effect of the solvent on the reaction rate is a complex phenomenon; however changing the solvent of the system constitutes vast information on particle formation mechanism since it affects the solubility of the polymerized species. Growth of colloidal silica was similarly studied with these solvents and preliminary results showed that an optimum size and distribution can be obtained for different alcohol environments.
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In-situ Synthesis of Nanoparticles on Layered Oxides.
Yuan Yao 1 , Girija Chaubey 1 , Jianxia Zhang 1 , K.G.Sanjaya Ranmohotti 1 , John Wiley 1
1 Department of Chemistry and Advanced Materials Research Institute, University of New Orleans, New Orleans, Louisiana, United States
Show AbstractSynthesis of nanoparticles (NPs) with controllable morphology directly onto supporting substrates is important to both nanomaterials research and applications in catalysis. We present a general two-phase synthetic method for the in-situ preparation of stabilized gold and iron oxide NPs on the surfaces of a series of exfoliated layered niobium and tungsten oxides. The size and dispersion of NPs can be readily adjusted by varying relative concentrations, the nature of the surfactant, the solvent system, etc. Details on the synthesis and characterization of various nanoparticle layered-oxide composites will be presented and selective attachment of specific NPs discussed.
9:00 PM - EE9.43
Preparation and Thermoelectric Performance of Nb-doped TiO2 / SrTiO3 Micro Composite System.
Kiyoshi Fuda 1 , Tomoyoshi Shoji 1 , Shigeaki Sugiyama 2
1 Applied Chemistry for Environment, Akita University, Akita-City Japan, 2 , Akita pref. Ind. Tech Center, Akita-City Japan
Show AbstractWe have conducted an investigation of micro composite system aiming at high performance thermoelectric metal oxides, reported already some findings concerning thermoelectric properties of Nb-doped TiO2 / SrTiO3 composites elsewhere. Here we have extended the composition range wider to find optimum conditions for higher performance. The composites were prepared via two processing steps: (1) precursor oxide preparation by wet processes; (2) sintering by using spark plasma sintering (SPS) apparatus. The composition of the composites and the sintering temperatures were selected in a region where a perovskite SrTiO3 and a rutile TiO2 phases would coexist in stable. In this study, the atomic ratio, Ti/Nb, in the samples was fixed 4/1, whereas, the atomic ratio, Sr/(Ti+Nb) was varied in a range between 0.2 and 1.0. The samples prepared here were found to be mainly constructed of rutile(TiO2) and perovskite(STO) crystals of about 1 μm in diameter baring a mosaic-type texture. The Seebeck coefficient, S, and electric conductivity, σ, were measured by using ULVAC ZEM-1 instrument, and thermal conductivity, κ, was determined by using NETZSCH LFA thermal analyzer in the temperature range between room temperature and 800 °C. From the composition dependence of TE properties, there seems to be a transition at around Sr/(Ti+Nb) = 0.6. In the Sr-rich region, higher σ, lower κ, and smaller S values were observed as compared to the Sr-poor region. It is interesting that low thermal conductivity and high electrical conductivity are simultaneously appeared in the Sr-rich region, where certain amount of rutile phase coexists with perovskite phase. The largest dimensionless figure of merit, ZT was found at Sr/(Ti+Nb) = 0.8, giving a value of 0.27 at 800 °C.
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ELNES of Ti-doped SiO2 Glass Using First-principles Calculations.
Tomoyuki Tamura 1 , Shingo Tanaka 2 , Masanori Kohyama 2
1 Center for Fostering Young and Innovative Researchers, Nagoya Institute of Technology, Nagoya-shi, Aichi, Japan, 2 Research Institute for Ubiquitous Energy Devices, National institute of advanced industrial science and technology, Ikeda-shi, Osaka, Japan
Show AbstractTitanium-doped SiO2 glass has several interesting physical properties and technological importance. The thermal expansion coefficient of this glass can be adjusted to near zero by controlling the Ti content. Recently, Ti-doped silica glass was chosen as a material for reflective mirrors in the EUV lithography. To understand the thermal expansion of Ti-doped silica glass, it is necessary to determine the role of Ti ions in the atomic and electronic structure. By combining EELS with modern STEM, the spatial resolution of EELS can readily reach sub-nanometer scale, enabling investigation of atomic and electronic structure with very high spatial resolution, and recently has been applied to Ti-doped silica glass. For more detailed understanding, theoretical ELNES spectra are necessary. We have recently installed the computational function of ELNES spectra to our in-house QMAS (Quantum MAterials Simulator) code based on the first-principles PAW method and have calculated the O K-edge spectra for pure silica glass and Ti-doped silica glass supercells with an excited pseudopotential which includes an core hole. We have found that pre-edge peaks are generated below the edge threshold energy of pure silica glass by Ti-doping, and have confirmed that these peaks originate from the hybridization between O-2p and Ti-3d using a real-space analysis technique.
9:00 PM - EE9.45
Modelling of Contacting Interfaces in Solar-cells.
Keith Butler 1 , Ole Martin Lovvik 3 , Jesper Friis 2 , Astrid Marie Muggerud 2 , Heidi Nordmark 2 , Per Erik Vullum 2 , John Harding 1
1 Engineering Materials, University of Sheffield, Sheffield United Kingdom, 3 , SINTEF, Oslo Norway, 2 , SINTEF, Trondheim Norway
Show Abstract The interface between silicon and silver is of fundamental importance in commercial solar cells, as it is known to contribute significantly to performance loss in solar cells. Despite the fact that thick film metallisation (the process most commonly used to form contacts in solar cells) has been used since the 1970s, little is known about the factors which affect the process beyond empirical observations. Few modelling studies of this interface have been performed and those which have been tend to concentrate on silver clusters on silicon surfaces [1, 2]. In this presentation we will examine a number of fundamental questions relating to the contacting interface, using a mixture of first-principles and semi-empirical potential based modelling as well as transmission electron microscopy (TEM). We use a newly developed potential for the silicon/silver interface, which incorporates elements of the embedded atom model (EAM) and Tersoff model.The validity of this model is demonstrated by comparison to first-principles calculations of interface geometries and energies, as well as comparison of simulated TEM images of the interface with experimental images of the same system. The potential is then used to explore the conformational landscapes of a number of important silicon-silver interfaces, allowing us to evaluate the most energetically favourable configurations. In addition we investigate the effects of plastic and elastic strain, due to lattice mis-match. The geometries generated from semi-empirical simulations are then used as the starting point for first-principles studies of the electronic structure of these interfaces, which provide more detailed information regarding the most desirable contact formations for improved current transfer.References.[1] J. K. Bording, B. Q. Li, Y. F. Shi, and J. M. Zuo. Size- and shape-dependent energetics of nanocrystal interfaces: Experiment and simulation. Phys. Rev. Lett., 90(22):226104,2003.[2] Hojin Jeong and Sukmin Jeong. Segregation of h as a surfactant during the formation of an Ag cluster on H-terminated Si(111): First-principles total-energy calculations. Phys. Rev. B, 73(12):125343,2006.
9:00 PM - EE9.46
Photoluminescence Enhancement of ZnS:Mn Nanoparticles by Surface and Crystallinity Control
Jongmin Kim 1 , Dae-Ryong Jung 1 , Dongyeon Son 1 , Byungwoo Park 1
1 Materials Science and Engineering, Seoul National University, Seoul Korea (the Republic of)
Show AbstractTo understand the effect of surface and crystallinity on the photoluminescence properties of nanoparticles, Mn-doped zinc sulfide nanoparticles were synthesized by a liquid-solid-solution method for preparing monodispersed nanocrystals with a diameter of 7.3 ± 0.7 nm. The influence of doping concentration for optimum luminescence properties was studied with the nonuniform distribution of local strain and the capping effect. The improved photoluminescence properties of the 450°C-annealed samples with 1.0 at. % Mn doping (quantum efficiency: ~16%) are attributed to both the removal of water/organics and the enhanced crystallinity. Additionally, highly luminescent surface-passivated ZnS:Mn nanoparticles were synthesized by a simple one-step lithium addition. Compared to the pristine Mn-doped zinc sulfide nanoparticles, the Li-added ZnS:Mn exhibited significantly enhanced luminescence properties (quantum efficiency: ~36%). The photoluminescence enhancement is due to the formation of an effective surface-passivation layer induced by lithium, and consequent suppression of the nonradiative recombination transitions. [1] D. Son, D.-R. Jung, J. Kim, T. Moon, C. Kim, and B. Park,
Appl. Phys. Lett. 90, 101910 (2007). [2] D.-R. Jung, D. Son, J. Kim, C. Kim, and B. Park,
Appl. Phys. Lett. 93, 163118 (2008). Corresponding Author: Byungwoo Park:
[email protected]9:00 PM - EE9.47
Surface-Passivation Effects on the Photoluminescence Enhancement in ZnS:Mn Nanoparticles by Ultraviolet Irradiation with Oxygen Bubbling
Dae-Ryong Jung 1 , Jongmin Kim 1 , Byungwoo Park 1
1 Materials Science and Engineering, Seoul National University, Seoul Korea (the Republic of)
Show AbstractThis study examined the effects of surface-passivation on the photoluminescence (PL) properties of ZnS:Mn nanoparticles treated by ultraviolet (UV) irradiation with oxygen bubbling. Compared to the pristine Mn-doped zinc-sulfide nanocrystals (quantum efficiency: ~16%), the UV-irradiated ZnS:Mn showed significantly enhanced luminescence properties (quantum efficiency: ~35%). The photoinduced surface passivation was characterized by x-ray diffraction, x-ray photoelectron spectroscopy, and time-resolved PL. The optimum thickness of the passivation layer for the quantum efficiency was examined considering the nanocrystal size, local strain, and radiative/nonradiative recombination rates. [1] D.-R. Jung, J. Kim, and B. Park,
Appl. Phys. Lett. 96, 211908 (2010). [2] D.-R. Jung, D. Son, J. Kim, C. Kim, and B. Park,
Appl. Phys. Lett. 93, 163118 (2008). Corresponding Author: Byungwoo Park:
[email protected]9:00 PM - EE9.5
Microstructure Properties of Powders and Ceramic Bodies of Lanthanum Modified PZT Nanoparticles Synthesized by Means the Oxidant-peroxo Method (OPM).
Mayra Goncalves 1 , Elson Longo 2 , Emerson Camargo 1
1 Chemistry Department, Universidade Federal de São Carlos, São Carlos, São Paulo, Brazil, 2 Chemistry Institute, Universidade Estadual Paulista, Araraquara, São Paulo, Brazil
Show AbstractWe report an alternative wet-chemical route that has been developed to prepare ferroelectric lead based materials, usually referred as the Oxidant-peroxo method (OPM). One of the advantages of this method is the absence of some contaminants, such as graphitic carbon and residual chlorite, which can be deleterious for the desired structural and electrical properties1,2. The OPM route is based on oxy-reduction reactions between Pb(II), Zr(II) and La(III) ions and titanium-peroxo-complex [Ti(OH)3O2]- at high pH, resulting in an amorphous precipitate that can be crystallized during the calcination step through an solid state mechanism. The goals of this work, were synthesize Pb(Zr1-xTix)O3 and (PbyLa1-y)(Zr1-xTix)O3 powders (where x=20 and 80%; y=95% in mol) by means the OPM route, submit these powders to heat treatments at 500 to 900oC and built dense ceramic bodies by sintering process at 1000-1100oC in conventional and microwave furnace. To characterize these materials in terms of microstructure properties Differential Scanning Calorimetry (DSC), X-ray Diffraction (DRX), Raman Spectroscopy (FT-Raman) and Scanning Electron Microscopy (SEM) were performed. The results showed that the amorphous precipitate is formed by spherical nanoparticles with sizes around 10nm. All powders were partially sintered after heat treatments at 700oC but still maintaining nanometric dimensions, with sizes between 30 and 60nm, indicating that reactive nanoparticles with high sinterability can be prepared by this method. The compositions richer in Ti showed tetragonal structure related to the P4mm space group and the phase transition occurred at 490oC, while those Zr-rich compositions are rhombohedral belonging to the R3c space group with phase transition around 530oC. The effects of the substitution of 5% in mol of lead ions by lanthanum ones at perovskite structure could be observed in some aspects when compared with the compositions without this rare earth element, such as (i) decrease of the unit cell volume; (ii) suppression of the grain growth with the increase of the calcinations temperature. The microwave sintering process promoted ceramic bodies with slightly smaller and uniform grain structure when compared with that samples sintered at conventional furnace.
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Hollow Nanostructures by Partial Sintering of Mesoporous Nanoparticle Aggregate.
E. Anumol 1 , R. Mukherjee 2 , T. Chakrabarti 2 , T. Abinandanan 2 , N. Ravishankar 1
1 Materials Research Centre, Indian Institute of Science, Bangalore India, 2 Department of Materials Engineering , Indian Institute of Science, Bangalore India
Show AbstractHollow nanostructures find application in various fields such as catalysis, drug delivery and bio-encapsulation. A general method is developed for the synthesis of hollow nanostructures. The synthesis involves the partial sintering of nanoporous aggregate of the metal or oxide by annealing in air. On annealing the nanoporous aggregate of CeO2, a single crystalline hollow structure is formed where as the aggregates of Pt, SnO2 and TiO2 form polycrystalline hollow structures. The evolution of microstructure is controlled by various kinetic parameters such as bulk diffusion, surface diffusion, grain boundary diffusion and grain boundary mobility. In order to understand the influence of these various parameters on the evolution of microstructure, during the sintering of porous aggregate of nanocrystallites, a phase - field study is carried out on such a system. The simulation shows that higher surface atomic mobility promotes single hollow formation while the high grain boundary atomic mobility promotes shrinkage of the agglomerate.The study sheds light on the atomistic mechanisms of hollow formation and enables rational synthesis of such structures.
9:00 PM - EE9.7
Size, Shape and Chemistry-dependent Antibacterial Activity of Silver Nanostructures.
Nidhi Lal 1 , N. Ravishankar 1
1 Materials Research Centre, Indian Institute of Science, Bangalore India
Show AbstractEmergence of resistant bacterial strains against commonly used antibiotics poses a serious hurdle in public health management and thus efficient alternatives need to be developed. Silver, TiO2 and ZnO are known to exert their antimicrobial effects through wide-ranging mechanisms such as rupturing of bacterial cell wall, denaturing bacterial proteins and deactivating DNA which makes it difficult for microbes to develop resistance against such simultaneously acting disparate mechanisms. These factors make it critical to thoroughly study the effect of the size, shape, exposed facets and the composition of these materials on their anti-bacterial properties. In this study, we have investigated the shape dependence of antibacterial effects of silver nanostructures on two broad groups of bacteria, Gram +ve (B. Subtilis, S.aureus) and Gram –ve (E.Coli, P. aeruginosa). Simple wet chemical synthesis routes were employed to obtain silver nanoparticles, nanorods, nanocubes and nanotriangles. These nanostructures were characterized by XRD, UV-Visible spectroscopy, SEM and TEM. The antibacterial properties of these nanostructures were determined both in liquid medium and on solid agar plates. An additional quantification approach utilizing fluorescence-based assays, such as florescence microscopy and flow cytometry was used to discriminate between live and dead bacteria after their treatment with these nanostructures. An insight into the interaction of differently shaped silver nanostructures and bacteria has been accomplished using TEM studies.
9:00 PM - EE9.8
Nanoscale Heterostructures Based on ZnO with Enhanced Visible Light Harvesting Efficiency.
Paromita Kundu 1 , Parag Deshpande 2 , Ahin Roy 1 , Giridhar Madras 2 , N. Ravishankar 1
1 Materials Research Centre, Indian Institute of Science, Bangalore India, 2 Department of Chemical Engineering, Indian Institute of Science, Bangalore India
Show AbstractNanoscale hybrids of wide band gap semiconductors sensitized with quantum dots of narrow band gap materials are important for photocatalysis and solar cell applications. Interfaces play a crucial role for electron transport in these sensistized systems. Here we demonstrate a novel method for tethering narrow bandgap semiconductor nanoparticles (CdS, in particular) to ZnO nanorods to produce nanoscale heterostructures with controlled interfaces that exhibit exceptional photocatalytic activity under solar light. This is achieved through a forced heterogeneous nucleation of a metal-precursor phase (say nitrate) on the surface of the ZnO and a subsequent sulfidation to convert the metal-precursor to the metal sulfide. This method enables the formation of a direct interface between the metal sulfide nanoparticles and the ZnO surface. A control over loading, composition, morphology and size of the sulfide nanoparticles could be achieved without using any template. The method has been demonstrated for the case of CdS and can be extended to other II-VI and III-V dots for solar cell and photocatalytic appliations. Materials characterization involves transmission electron microscopy, x-ray photoelectron spectroscopy and UV-Visible diffuse reflectance spectroscopy.
9:00 PM - EE9.9
Dielectric Properties of TiO2 and Zr−doped TiO2 Thin Films Prepared by Metalorganic Decomposition.
Chandra Thapa 1 , Chandran Sudakar 1 , M. Sahana 1 , Vaman Naik 2 , K. Padmanabhan 1 , R. Naik 1
1 1Department of Physics and Astronomy, Wayne State University, Detroit, Michigan, United States, 2 Department of Natural Sciences, U Michigan-Dearborn, Dearborn, Michigan, United States
Show AbstractThe leakage current and photocatalytic performance of TiO2 can be improved by properly doping Ti with other transition metal cations. For example, Zr4+ doping for Ti4+ can significantly improve the desired properties. We have studied the properties of pure TiO2 and Zr−doped TiO2 thin films prepared by metalorganic decomposition (MOD) technique and annealed at temperatures from 650 to 950 oC. Both XRD and Raman spectra show TiO2 to be mostly in anatase form below the annealing temperature of 850 oC and in rutile phase above 850oC. However, the Zr doping prevents rutile phase formation even at at 950 oC. We have studied I−V characteristics and frequency dependence of dielectric constants of pure and Zr−doped TiO2 in the frequency range of 100Hz–1MHz. We find an improvement in leakage current with increasing annealing temperature from 650 to 950 oC for both TiO2 and Zr−doped TiO2, but no appreciable improvement in the leakage current upon Zr doping. The dielectric constant of pure TiO2 films improves from 30 to 80 with increasing annealing temperature, whereas that of Zr−doped TiO2 is independent of annealing temperature and its value is ~50 at 30 kHz. This may be attributed to the persistence of anatase phase of TiO2 over wide range of annealing temperatures for Zr−doping. These properties and their implications for different applications will be discussed.
Symposium Organizers
P. Shiv Halasyamani University of Houston
David G. Mandrus The University of Tennessee/Oak Ridge National Laboratory
Kyoung-Shin Choi Purdue University
Simon J. Clarke University of Oxford
EE10: Wide-band-gap Semiconductors and Catalytic Materials
Session Chairs
Thomas Bein
Cameron Kepert
Thursday AM, December 02, 2010
Ballroom A, 3rd floor (Hynes)
9:30 AM - **EE10.1
Photoelectrochemistry of Complex Oxides for Dye-sensitized Solar Cells.
Gayatri Natu 1 , Yiying Wu 1
1 Chemistry, Ohio State University, Columbus, Ohio, United States
Show AbstractComplex oxides have been used for applications such as the transparent conductive oxides, dye sensitized solar cells and photocatalysis. For these applications, it is fundamentally important to investigate theirs band structures and the oxide/electrolyte interfacial properties. In this talk I will use Zn2SnO4 and CuAlO2 as examples to talk about our systematical study on the their energetics of the conduction band and valence band by optical, electrochemical and photoelectrochemical methods. These results and methods are valuable to the developments of new materials for photovoltaics and photocatalysis. The use of Zn2SnO4 and CuAlO2 in dye-sensitized solar cells will be discussed.
10:00 AM - EE10.2
Surface Phase Diagram of ZnO (10-10) Surface in Thermodynamic Equilibrium with Oxygen and Hydrogen.
Satyesh Yadav 1 , Ghanshyam Pilania 1 , Ramamurthy Ramprasad 1
1 CMBE, University of Connecticut, Storrs, Connecticut, United States
Show AbstractThe band edge energy levels of ZnO encloses the H2 reduction and the O2 oxidation potentials. This makes ZnO a promising candidate for photocatalytic splitting of water to produce O2 and H2. Since the interaction of the ZnO surfaces with H2, O2, and H2O forms the basis of such photocatalytic reactions, it is crucial to understand thermodynamics and kinetics underlying reactions involving ZnO surfaces. As a first step in this direction, we present the surface phase diagram of the ZnO (10-10) surface in thermodynamic equilibrium with H2 and O2, determined using first principles thermodynamics.All calculations were done using Density Functional Theory (DFT) in combination with statistical thermodynamics enabling the introduction of pressure and temperature and thereby resulting in phase diagrams. Molecular surface coverages ranging from a complete overlayer to a partial 1/6 monolayer of various species, including OH, H, H2, O, H2O, half dissociated (HO-Zn-O-H) H2O and O vacancy were considered on the ZnO (10-10) surface. The total free energy of adsorption of a given molecular species at a given coverage involved the DFT total energies, the free energy (or the chemical potential) of the corresponding gas phase species within the ideal gas approximation, as well as the vibrational entropy contribution of adsorbed species within harmonic oscillator approximation. The surface phase diagrams were constructed using a few popular electron exchange and correlation approximations within DFT, such as the LDA, LDA+U, and GGA. These results were found to be qualitatively similar indicating that the level of approximation within DFT is not expected to alter the nature of the results dramatically. We find that the ZnO clean surface dominates at low chemical potentials of O2 and H2, and highly concentrated half dissociated H2O is favored at high chemical potential of O2 and H2. Atomic hydrogen adsorption dominates at low chemical potential of O2 and high chemical potential of H2 while oxygen vacancies are favored at very low chemical potential of O2. Thus we conclude that the dominant reactions at this ZnO surface will involve dissociation of water, atomic hydrogen adsorption and oxygen vacancy formation.
10:15 AM - EE10.3
Excitonic Behaviour in 2-D TiO2 Anatase Systems: A First-principle Investigation.
Maurizia Palummo 1 , Giacomo Giorgi 2 , Letizia Chiodo 3 , Koichi Yamashita 2
1 Physics, ETSF,Tor Vergata University, Roma Italy, 2 Chemical System Engineering, Tokyo University, Tokyo Japan, 3 IIT Italian Institute of Technology, Center for Biomolecular Nanotechnologies, Lecce Italy
Show AbstractTransition metal oxides are of strong interest for their potential applicability in photonics, electronics, photovoltaics (PV), and light emitting device technology.They are characterized by a high degree of polymorphism.Rutile, anatase, and brookite are the main phases of titanium dioxide. While brookite is detected both experimentally and theoretically as the thermodynamicallymost unstable, rutile and anatase are almost degenerate at ordinary conditions of P and T, with the former experimentally slightly more stable.Both rutile and anatase have a tetragonal cell, differing only for the orientation among octahedral chains.This small difference in geometry is responsible for the more marked difference in electronic and optical properties between the two polymorphs.Although Titanium dioxide is one of the most studied oxides materials due to its primary role in photocatalysis and photovoltaics applications, a first-principles analysis, beyond the single-particle approach, of the electronic and optical properties of its two-dimensional systems and/or surfaces is still missing.Being the anatase form particular attractive for optoelectronic applications and due to the fact that, at nanoscale, such polymorph is reported to be more stable than rutile, we focus here on the (001) and (101) slabs. The (001)-(1x1) model results highly unstable, anyway, due to the concomitant presence of both the surface terminations in TiO2 nanostructures and also to the fact that minority surfaces can be the principal source of active sitesfor the photocatalytic production of H2, novel models for the reconstruction of (001) surfaces have been proposed.In particular, a (1 x 4) reconstruction seems to be the most “appealing”, able to reproduce experimental results (STM, RHEED, LEED, and XPS).Different interpretations have been suggested to explain the stability of this reconstruction of the (001) anatase surface: stress reduced amount, (ADM “ad molecule” [2]), microfaceting toward the (103) and (10-3)surface planes [3], and added-missing row based models [4].In this work, we move from a DFT [5] analysis of the basic structural and electronic properties of several (001) and (101) TiO2 2-D models and then we investigate their optical properties including, in a first-principles manner,the electron-hole interaction within the Bethe-Salpeter equation (BSE) approach [6].These calculations reveal a rich excitonic behavior, as function of the slab thickness and of the surface reconstruction, which could plays a role in the different photo-catalytic properties observed in the experiments.[1] B. O'Regan and M. Grätzel, Nature 353 (1991) 737.[2] M. Lazzeri, A. Selloni, Phys. Rev. Lett. 87, (2001) 266105[3] G. S. Hermann et al. Phys. Rev. Lett. 84, (2000) 3354.[4] Y. Liang et al. Phys. Rev. B 63, (2001) 235402.[5] VASP, Version 4.6.36, http://cms.mpi.univie.ac.at/vasp/
10:30 AM - EE10.4
Designing Semiconductors with Light Harvesting Optimized for Solar Water Splitting.
Peter Khalifah 1 2 , Limin Wang 2 , Alexandra Reinert 1 , Andrew Malingowski 1 , James Ciston 2 , Peichuan Shen 1 , Alexander Orlov 1 , Wei Kang 2 , Mark Hybertsen 2 , Bruce Ravel 3 , Emil Bozin 1
1 , Stony Brook University, Stony Brook, New York, United States, 2 , Brookhaven National Laboratory, Upton, New York, United States, 3 , National Institutes of Standards and Technology, Gaithersburg, Maryland, United States
Show AbstractWhile solar photoelectrolysis is a promising method for the renewable production of H2 fuel, there are currently no semiconductors which can efficiently utilize solar light to drive this process. Our efforts to understand the factors limiting efficiencies and to design materials that overcome these barriers will be described. Recent advances in our group include the discovery of families (including new structure types) of oxide semiconductors with band gaps as small as 2.7 eV which are capable of direct photoelectrolysis, and improved syntheses and structural insights into oxynitrides with band gaps as small as 2.0 eV.
10:45 AM - EE10.5
Tuning Band Gaps in the [Cu2S2][Sr3Sc2O5] Structure by Cation Replacement: Predicting New p-type Oxide Semiconductors Using Hybrid Density Functional Theory.
David Scanlon 1 , Graeme Watson 1
1 School of Chemistry, Trinity College Dublin, Dublin, Leinster, Ireland
Show AbstractTransparent conducting oxides (TCOs) are vital components in Solar cells, flat panel displays etc.[1] Although most of the industry standard TCOs are n-type (e.g. SnO2:F, In2O3:Sn and ZnO:Al), the development of p-type TCOs has proved very challenging.[2] Since the discovery of concomitant p-type conductivity and transparency in thin films of CuAlO2,[3] the development of p-type TCOs has enjoyed an explosion of interest. This has resulted in the identification of other copper delafossite materials with p-type TCO properties (CuMO2, M – Ga, In, B, Sc, Y, Cr).[4, 5] As these materials are all either limited by an indirect band gap or low conductivity, or both, alternative Cu(I)-based materials have been investigated. SrCu2O2 was also found to have p-type ability and transparency, even having a direct band gap, but with lower conductivities even than the delafossites.[6] Transparent p-n junctions using n-type ZnO and p-type SrCu2O2 have been fabricated by Hosono and co-workers, but these possible UV LEDs for solid state lighting, have suffered from extremely poor performance, due mostly to the poor p-type conductivity of SrCu2O2.[7]Layered oxychalcogenides have emerged from the field of Cu(I) based materials as alternative p-type TCOs, often possessing large optical bandgaps and good hole mobility due to favourable mixing between Cu d states and Ch p states at the VBM.[8] [Cu2S2][Sr3Sc2O5] has recently come to light as a promising candidate, having the highest undoped conductivity of any p-type TCO and a higher hole mobility than In2O3:Sn.[9] In this study we analyse the electronic structure and geometry of [Cu2S2][Sr3Sc2O5] using a screened hybrid density functional approach (HSE06).[10] We investigate the optimization of transparency in this material through cation substitution and discuss strategies to improve the conductivity of these materials.
[1] Gordon, R. G. MRS Bull. (2000), 25, 52–57.
[2] Thomas, G. Nature (1997), 389, 907.
[3] Kawazoe, H.; Yasakuwa, H.; Hyodo, H.; Kurita, M.; Yanagi, H.; Hosono, H. Nature (1997), 389, 939.
[4] Marquardt, M. A.; Ashmore, N. A.; Cann, D. P. Thin Solid Films (2006), 496, 146–156.
[5] Scanlon, D. O.; Walsh, A.; Watson, G. W. Chem. Mater. (2009), 21, 4568–4576.
[6] Kudo, A.; Yanagi, H.; Hosono, H.; Kawazoe, H. Appl. Phys. Lett. (1998), 73, 220–222.
[7] Ohta, H.; Hosono, H, Mater. Today (2004), 7, 42-51.
[8] Ueda, K.; Hiramatsu, H.; Hirano, M.; Kamiya, T.; Hosono, H. Thin Solid Films (2006), 496, 8–15.
[9] Liu, M. L.; Wu, L. B.; Huang, F. Q.; Chen, L. D.; Chen, I. W. J. Appl. Phys. (2007), 102, 116108.
[10] Scanlon, D. O.; Watson, G. W. Chem. Mater. (2009), 21, 5435-5442.
11:00 AM - EE10: Nano
BREAK
11:30 AM - **EE10.6
Water Dissociation and Dynamics on GaN Surfaces: Link between Surface Chemistry of Water and Photocatalysis.
Maria Victoria Fernandez-Serra 1
1 Physics and Astronomy, Stony Brook University, Stony Brook, New York, United States
Show AbstractEfficient solar water-splitting requires a good catalyst to oxidize water into O2 with the photo-holes. Efficient water oxidation catalysts are hard to find. The solid solution of wurtzite GaN/ZnO is a water-splitting photocatalyst which works in visible light(1),while pure GaN is a water-splitting photocatalyst which works in UV(2). Unlike other semi-conductors, the surfaces of both materials exhibit high efficiencies for water oxidation. Water splitting can occur if the semiconductor conduction and valencebands lie respectively above and below the redox potentials for hydrogen reduction(2H+ + 2e- --> H2) and water oxidation (2H2O + 4h+ --> O2 + 4H+). All knownsemiconductors that meet this energy criterion are deficient in other respects, usually splittingwater efficiently only with ultraviolet light, and inefficiently with visible light. We present a first-principles molecular dynamics study of water at the(10-10) surface of wurtzite GaN. We show how spontaneous dissociation of water is an important requirement for photoactive semiconductor surfacesthat, due to their absorption in the visible, have a low overpotential for water oxidation.Based on the chemical species obtained at the GaN/water interface from our simulations, wepropose the key intermediates of a four-step mechanism for water oxida-tion on this surface. We argue that our mechanism shouldlikely apply to other semiconductor surfaces.(1) K. Maeda et al., Nature 440, 295 (2006)(2) K. Maeda et al., Bull. Chem. Soc. Jpn. 5, 1004 (2007)(3) X. Shen, Y. A. Small, J. Wang, P. B. Allen, M. V. Fernandez-Serra, M.S. Hybertsen and J. T. Muckerman, "Photocatalytic Water Oxidation atthe GaN (1010)-Water Interface," J. Phys. Chem. C 114
12:00 PM - EE10.7
Defects and Grain Boundary Properties in Cu-doped ZnO Using Dielectric Functions.
Youn-Woo Hong 1 , Jae-Ho Lee 1 2 , Hyo-Soon Shin 1 , Dong-Hun Yeo 1 , Joo-Ho Moon 2 , Jong-Hee Kim 1
1 , Korea Institute of Ceramic Engineering & Technoloy, Seoul Korea (the Republic of), 2 , Yonsei University, Seoul Korea (the Republic of)
Show AbstractZnO is a wide bandgap semiconductor ceramic with numerous applications, such as transparent electronics, spintronic devices, sensors, and varistors. All of these applications are either affected by, or depend on, defects and grain boundary properties according to various dopants. Among impurities p-type CuO doped ZnO systems have not been developed simultaneously for the change of defect levels and grain boundary characteristics. In this study we have investigated the electric and dielectric properties on 0.1~5.0 at% CuO doped-ZnO by using dielectric functions (Z*, M*, ε*, Y*, and tanδ) including admittance and impedance-modulus spectroscopy. For the identification of the bulk trap levels, it is useful to examine the zero-biased admittance spectroscopy as a function of frequency and temperature. Impedance and electric modulus spectroscopy is a powerful technique to characterize the grain boundaries of ceramic materials as well. First of all, the dielectric constant and loss were measured with frequency at room temperature. Especially the dielectric loss peaks about 2 irrespective of CuO contents were shifted to low frequencies. The defect trap levels were shifted linearly with CuO contents of 0.2 eV to 0.7 eV by electric modulus spectroscopy. Also we have compared the activation energies and capture cross-sections to identifying the defects with admittance spectroscopy. However, the interface state levels were somewhat similar to 0.96~1.10 eV with CuO contents. From these results it will be discussed the reasons of which the change of electric and dielectric properties with CuO contents in ZnO including the microstructure and its applications.
12:15 PM - EE10.8
A DFT and HRTEM Study on MoS2/Co: Locating Promoters in Catalytic Nano-structures.
Manuel Ramos 1 2 , Gilles Berhault 3 , Domingo Ferrer 4 , Brenda Torres 2 , Russell Chianelli 2
1 Fisica y Matematicas, UACJ, Juarez, Chihuahua, Mexico, 2 Materials Research and Technology Institute, UTEP, El Paso, Texas, United States, 3 Institut de Recherches sur la Catalyse et l’Environnement, IRCELYON-University of Lyon, Villeurbanne, Lyon, France, 4 Microelectronics Research Laboratory, UT-Austin, Austin, Texas, United States
Show AbstractA highly active unsupported Co/MoS2 catalyst for the hydrodesulphurization (HDS) of dibenzothiophene (DBT) was studied in order to characterize the MoS2/Co9S8 interface in which a strong synergetic effect is observed. Combining HRTEM characterization with TEM simulations from constructed molecular model we developed a description of the local structure of the interface between MoS2 and Co9S8 supported by experiment in catalysts stabilized in the reaction environment. This approach coupled with determination of the electronic properties through DFT calculations suggests that the synergetic effect results from a change in both Mo coordination and electronic properties resulting in the creation of open latent vacancy sites and of a stronger metallic character at the region close to the Fermi level. Electron donation from cobalt through intermediate sulfur atom is also observed for non-completely coordinated atoms presenting direct Co-Mo bonds resulting in a strong weakening of the Mo-S bond strength in Mo-S-Co entities present at the interface region. A unified interpretation of the synergy effect is then proposed corroborating results acquired previously in our electronic theory for promotion.
12:30 PM - EE10.9
Aerosol Synthesis of Bi2WO6 for Photocatalytic Applications.
Sara Skrabalak 1
1 Chemistry, Indiana University, Bloomington, Indiana, United States
Show AbstractBi2WO6 is a promising visible light (λ > 400 nm) photocatalyst. Here, ultrasonic spray pyrolysis (USP), an aerosol synthetic technique, is used to prepare Bi2WO6 particles of different shapes and architectures. The different particle morphologies arise from different precursor combinations and are attributed to their corresponding decomposition pathways. Prepared materials were characterized by scanning and transmission electron microscopy, powder X-ray diffraction, X-ray photoelectron spectroscopy, diffuse reflectance measurements, and BET surface and BJH pore size analysis. Dye degradation studies were also performed, with the USP-prepared samples being compared to Bi2WO6 synthesized by conventional solid-state heating of the parent oxides.
12:45 PM - EE10.10
Origin of the Enhanced Reducibility of Ce1−x(Pd/Pt)xO2: Importance of Dopant Geometry and Crystal Field Splitting.
David Scanlon 1 , Benjamin Morgan 1 , Graeme Watson 1
1 School of Chemistry, Trinity College Dublin, Dublin, Dublin, Ireland
Show AbstractDoping CeO2 with Pd or Pt has been shown to increase the oxygen storage capacity (OSC) and the catalytic activity of this environmentally important material.[1-4] To date, however, a nanoscopic understanding of why the OSC is increased has been lacking. We present a comprehensive density functional theory analysis of Pd- and Pt-doped CeO2, and show conclusively that the increased OSC is caused by a large distortion of the Pd/Pt ions off the Ce lattice site. Pd(II)/Pt(II) (in a d8 configuration) moves by ~1.2 Å off the Ce site to adopt a square-planar coordination, leaving three 3-coordinate oxygen atoms. These under-coordinated oxygens are easier to remove, and are the reason for the observed increased OSC. Our results highlight the importance of rationalizing the preferred coordination environments of both dopants and host cations when choosing suitable dopants for next generation catalysts. In light of this, we propose guidelines for the rational design of novel doped oxide catalysts.
[1] M. S. Hegde et al., Acc. Chem. Res. 42 (2009) 704
[2] P. Bera et al., Chem. Mater. 15 (2003) 2049
[3] P. Bera et al., Chem. Mater. 14 (2002) 3591
[4] S. Roy et al., Appl. Energy 86 (2009) 2283
EE11: Porous Materials and Metal-Organic Frameworks
Session Chairs
Kyoung-Shin Choi
Yiying Wu
Thursday PM, December 02, 2010
Ballroom A, 3rd floor (Hynes)
2:30 PM - **EE11.1
Integrated Functional Pores by Soft Porous Crystals.
Susumu Kitagawa 1
1 iCeMS, Kyoto University, Kyoto, Kyoto, Japan
Show AbstractThe recent advent of porous coordination polymers (PCPs) or Metal Organic Frameworks (MOFs) as new functional microporous materials, have attracted the attention of chemists and physicists due to not only scientific but also application interest in the creation of unprecedented regular nano-sized spaces and in the finding of novel phenomena.[1-3] We have found flexible porous frameworks, which respond to specific guests, dissimilar to the conventional porous materials. We call this new material as “soft porous crystal (SPC)”,[4] which is defined as solids possessing both highly ordered network and structural transformability. SPCs provide us with various unique functions on confinement and recognition of guest molecules, which are applicable for a specific gas separation for air or exhausts. They also afford the efficient reaction vessels, which allow controlled living radical polymerization as well as stereoregulated polymerization of substituted acetylenes.Very recently, we have provided bidirectional chemo-switching SPC with the aid of spin crossover properties and a highly proton conductive aluminum PCP having one-dimensional imidazole Aggregate at high temperature.1.S. Kitagawa, et.al., Angew. Chem. Int. Ed,, 2004, 43, 2334 (Reviews). 2.T.Uemura, et.al., Chem.Asian J. 2006. 1. 36. (Focus Review). 3. T.Uemura et.al., Chem.Soc.Rev.2009, 38, 1228. 4. S.Horike, et.al., Nature Chemistry, 2009,1,695. (Reviews).
3:00 PM - EE11.2
Structural Investigation of Porous Oxides for CO2 Capture Applications.
Winnie Wong-Ng 1 , Laural Espinal 1 , James Kaduk 2 , Qing Huang 1 , Andrew Allen 1 , Chun Chiu 1 , Leonid Bendersky 1 , Igor Levin 1 , Martin Green 1 , Anais Espinal 3 , Hector Garces 3 , Steven Suib 3
1 , NIST, Gaithersburg, Maryland, United States, 2 , Polycrystallography Inc., Naperville, Illinois, United States, 3 Chemistry, University of Connecticut, Storrs, Connecticut, United States
Show AbstractAs coal-burning power plants are an important part of energy production for the foreseeable future, reduction of CO2 emissions from these plants using efficient and low cost sorbents is important for global sustainability. Current examples of state-of-the-art solid sorbent materials include metal-organic-framework (MOFs), activated carbon, and molecular sieves such as zeolites. Framework tunability similar to zeolites has been observed in a class of molecular sieve materials consisting of mixed-valence manganese oxides. The lattice framework of these manganese oxides is chemically distinct from zeolites. The structure characteristics of these materials include edge-sharing and vertices-sharing octahedral frameworks with channels (OMS) and frameworks with layers (OL). Crucial factors for understanding the efficiency of porous sorbent materials include the framework and pore structure, and the chemical and physical reactivity of CO2 with the pores. This talk will discuss the results of structural characterization of selected OMS and OL molecular sieves and of a NaY-zeolite with CO2 incorporation in the channels.
3:15 PM - EE11.3
Covalently Interconnected and Separated Vanadosilicate Shells.
Xiqu Wang 1 , Lumei Liu 1 , Allan Jacobson 1
1 Chemistry, University of Houston, Houston, Texas, United States
Show AbstractIn conventional heteropolymetalate clusters such as Keggin clusters the silicate tetrahedra are typically located inside the metal oxide shells. However, there are rare cases where pairs of silicate tetrahedra substitute for the metal polyhedra of the shell, giving rise to metal-silicate shells in the nanometer regime. Such shells are readily connected to form extended structures through Si-O-M bonds. To our knowledge, only a 1D chain structure and a 3D framework composed of covalently linked vanadosilicate shells are known. In the 1D structure, two pairs of silicate tetrahedra are on the opposite side of a [V16Si4O46] shell (Wang et al, Chem Comm, 2001, 2472), while in the 3D structure, four pairs of silicate tetrahedra are located on a [V14Si8O52] shell in a tetrahedral configuration (Tripathi et. al., J. Am. Chem. Soc., 2003,125,10528). In this work we report a 2D layered structure formed by covalently linking [V15Si6O46(OH)2] shells in the compound Cs9[(V15Si6O46(OH)2Cl)(V2O4)](H2O)x, P21/c, a=12.521(3), b=19.950(6), c=28.207(8)Å, β=101.97(1)°, and a 0D structure with separated [V15Si6O42(OH)6] shells in the compound ((CH3)4N)6[V15Si6O42(OH)6](H2O)x, P6122, a=15.385(3) Å c=61.22(1) Å.
4:30 PM - EE11.5
Tuning Metal-organic Frameworks for Hydrogen Storage Applications.
Michael Froeba 1 , Stephanie Wenzel 1 , Fischer Michael 1 , Frank Hoffmann 1
1 Department of Chemistry, University of Hamburg, Hamburg Germany
Show AbstractThe search for suitable porous materials for mobile gas (methane or hydrogen) storage applications is currently an active area of research. Various kinds of (micro)porous materials, like carbon nanotubes, hyper-crosslinked polymers, activated carbon etc., are considered for such applications. Due to their high specific surface areas and microporosity, MOFs (metal-organic frameworks) are optimal candidates for hydrogen storage based on physisorption [1]. Due to the relatively weak solid-fluid interactions hitherto very low temperatures are required for storage of hydrogen in these kind of materials. In order to strengthen the solid-fluid interactions it has been shown that two structural parameters of the host material are advantageous: (a) the incorporation of linkers, which should have a maximum polarisability, and (b) the existence of so-called ‘open metal sites’, i.e. coordinatively unsaturated metal centers [2].Concerning (a) we here present synthesis and characterization of a series of new linkers, which contain carbon, silicon, and germanium as sp3 centers, thereby varying systematically the polarisability of the molecules.The respective isoreticular MOF phases (UHM-2 [3], UHM-3 [4], UHM-4 [4]) exhibit the same structure as PCN-12 [5] with a ‘close packing’ alignment of dicopper paddle-wheel units i.e. coordinatively unsaturated metal centers and therefore should be interesting candidates for hydrogen storage applications. Beside common characterization by P-XRD, thermal analysis, and nitrogen physisorption particular attention was paid to different activation methods like thermal activation or solvent exchange, before the materials were investigated with respect to their hydrogen storage capacity and the resulting heats of adsorption. In addition, theoretical GCMC simulations of hydrogen adsorption [6] for the low and the high pressure regime are presented.References[1] Zhao, D.; Yuan, D.; Zhou, H.-C. Energy Environ. Sci. 2008, 1, 222.[2] Dinca, M.; Long, J. R. Angew. Chem. 2008, 120, 6870.[3] Wenzel, S. E.; Fischer, M.; Hoffmann, F.; Fröba, M. Inorg. Chem. 2009, 48, 6559.[4] Wenzel, S. E.; Fischer, M.; Hoffmann, F.; Fröba, M. 2010, in preparation.[5] Wang, X.-S.; Ma, S.; Forster, P. M.; Yuan, D.; Eckert, J.; López, J. L.; Murphy, B. J., Parise, J. B.; Zhou, H.-C. Angew. Chem. 2008, 120, 7373.[6] Fischer, M.; Hoffmann, F.; Fröba , M.; ChemPhysChem 2009, 10, 2647.
4:45 PM - EE11.6
The Role of Host-guest Interaction in Design of Metal-organic Framework Materials for Selective Gas and Drug Separation: Theoretical Aspects.
Rodion Belosludov 1 , Hiroshi Mizuseki 1 , Yoshiyuki Kawazoe 1
1 Institute for Materials Research, Tohoku University, Sendai, Miyagi, Japan
Show AbstractThe recent advent of metal-organic framework materials (MOFs), as new functional adsorbents has attracted the attention of chemists due to scientific interest in the creation of unprecedented regular nano-sized spaces and in the finding of novel phenomena, as well as commercial interest in their application for storage, for separation and in heterogeneous catalysis [1]. Thus, there is a continuously growing demand for optically pure compounds due to the important applications of such chemicals in pharmaceuticals, cosmetics and medicine. Thus, many drugs have two or more forms of the same chemical entity but the molecules arranged differently in space. Of the isomers, only one generally offers all the therapeutic benefits with the others having side-effects. Isolation of benefits results in smaller dosages with lesser side-effects. Recent works have demonstrated the high potential of MOF as a new class of chiral sorbents, capable of high stereo-selectivity in sorption and chromatographic separation of racemic mixtures [2]. The aim of this study is detailed theoretical analysis the adsorption of targeted molecules into selected metal-organic framework (MOF) materials. Together with experimental investigation it can create potential opportunities for selective gas and drug separation.Recently the high sorption ability for acetylene on MOF material (Cu2(pzdc)2(pyz), pzdc = pyrazine-2,3-dicarboxylate, pyz = pyrazine) was determined [3], using both extensive first-principles calculations and different experimental measurements, which ascribe to the double hydrogen bond support between the acidic acetylene proton and its acceptor basic site on the channel surface. In the nano-channel, acetylene molecules are indeed oriented to basic oxygen atoms and form a one-dimensional chain structure aligned to the host channel structure. It has been shown that the concept using designable regular MOF could be applicable to a highly stable, selective adsorption system. The absorption of several chiral sulfoxides, which constitute an important class of biologically active compounds and therapeutic drugs, into the Zinc(II) terephthalate lactate homochiral porous coordination polymer has been also investigated in collaboration with experimentalists [4] . The position of absorbed molecules has been determined and the detailed analysis of charge density distribution reveals the absorptions site as well the host-guest interactions. The present results indicate that selected MOF structures can be used for the stereo-selective separation and therefore can be applied for drug separation.REFERENCES[1] S. Kitagawa et al., Angew. Chem. Int. Ed. 43 (2004) 2334.[2] D. N. Dybtsev et al. Angew. Chem., Int. Ed. 45 (2006) 916.[3] R. Matsuda et al. Nature 436 (2005) 238.[4] D. N. Dybtsev et al. Chem.-Euro. J. (2010) accepted for publication.
5:00 PM - EE11.7
Structure and Luminescence in Metal Organic Frameworks.
Patrick Feng 1 , Scott Meek 1 , Stefan Nikodemski 1 , John Perry 1 , F. Doty 1 , Mark Allendorf 1
1 , Sandia National Laboratories, Livermore, California, United States
Show AbstractMetal-organic frameworks (MOFs) are a rapidly expanding category of nanoporous materials, many of which exhibit luminescent properties of interest for chemical sensing, radiation detection, and optoelectronics. In spite of the enormous synthetic flexibility available in these materials, the fundamental understanding required for rational design of luminescent frameworks has not been established. In this presentation, we will discuss an in-depth investigation we are conducting with the objective of understanding the relationship between MOF luminosity and important aspects of their structure, such as interchromophore distance and orientation, interpenetration, and trapped solvent. Our platform for this investigation is the IRMOF series, which allows linker electronic structure to be systematically tuned while preserving the overall crystalline structure. However, our results provide general insight into the factors controlling luminescence in many categories of MOFs. Specific aspects addressed in this presentation will include linker conjugation, exciplex formation, structural flexibility, and energy transfer between linker groups and infiltrated guest molecules. We will also address the luminescent properties of MOF-5 (IRMOF-1), for which a conflicting and confusing situation exists in the literature. Our results demonstrate that luminosity in MOFs is a complex phenomenon that involves subtle elements of structure and aspects of preparation that can be difficult to control and characterize.
5:15 PM - **EE11.8
Oriented Nanoscale Films of Metal-organic Frameworks via Gel-layer Synthesis.
Thomas Bein 1
1 Chemistry, University of Munich, Munich Germany
Show AbstractMetal-organic frameworks (MOFs) assembled from organic building blocks and metal-based connectors have attracted much interest due to their large pores and their enormous structural diversity. Particularly, the generation of homogeneous thin films of MOFs is highly desirable in view of potential applications including chemical sensors, catalysts as well as optical devices. We have recently developed direct growth methods from solution for oriented MOF layers on self-assembled monolayers. Here we present a novel strategy for the growth of highly oriented thin films of MOFs, based on the storage of one reaction partner for framework synthesis in a polymer gel layer, followed by diffusion of the other reaction partner into the gel layer and to a nucleation interface provided by a functionalized self-assembled monolayer. For example, we demonstrate that this new strategy enables the room temperature synthesis of oriented thin films of the two very different MOFs Cu-HKUST-1 and amino-functionalized Fe-MIL-88B, respectively. We anticipate that oriented thin film synthesis from gel layers can be generalized to many different MOF structures.