The search for materials with desired magnetic and electrical properties concomitantly relies on the discovery of new systems. To unequivocally determine the compounds&’ innate properties, large single crystals must be grown and characterized. In this talk, I will focus on the versatility and tunability of properties of intermetallics as it applies to the design and discovery of compounds with unusual magnetic and electrical properties. The challenges of phase stability, single crystal growth, structure determination, and physics of these materials will also be discussed.

Alkaline earth metals such as calcium and magnesium are low-melting and reactive toward many elements in the periodic table; this makes them useful as solvents for metal flux reactions. Their melting points can be lowered further by mixing them with other elements; a 50/50 Ca/Li mixture melts at 300 C, and eutectic mixtures of Mg/Al and Ca/Mg both melt at ca. 450 C. Reactions of iron with rare earths and silicon in Mg/Al fluxes produce complex multinary phases including R₅Mg₅Fe₄Al₁₂Si₆, R₃FeAl_4-xMg_xSi₂, and RFe₂Al_7-xMg_x (R = rare earth). All of these structures feature a similar building block of chains of face-sharing aluminum trigonal prisms which are centered by iron. Pseudo-Zintl phases such as CaMgSi and EuMgSn can also be grown in this flux; these compounds are close to a metal-insulator transition and exhibit interesting properties such as magnetoresistance. Calcium-rich fluxes are excellent solvents for carbon and CaH₂, enabling the formation of complex metal carbides and hydrides. These products range from charge-balanced salt-like Ca₁₁Sn₃C₈ and LiCa₂C₃H to phases incorporating a range of hydride and/or carbide interstitials, such as Ca₄₈In₁₃C_4-xH_23+x.

Topochemical reactions can be utilized to direct structure and properties in various compounds. Recent efforts in our group have involved the insertion of cation and/or anion species into layered perovskites via oxidative/reductive intercalation and/or ion exchange. In one case, we have found that the use of reductive intercalation with alkali metals, followed by oxidative intercalation with chalcogen hydride gases, allows for the construction of alkali-metal chalcogen hydride layers within Dion-Jacobson-type hosts; layered perovskites like RbLaNb2O7 can be manipulated to introduce Rb-ChH layers (ChH = OH, SH) within the interlayer. In other systems, two-for-one ion exchange reactions can be carried out on Ruddlesden-Popper perovskites; reactions of K2SrTa2O7 with divalent transition metal ions result in compounds of the form, MSrTa2O7 (M = Co, Zn). Details on the synthesis and characterization of these products will be presented with a discussion on the utility of these set of reactions for manipulations of other solids.

Development of new routes to magnetic materials is a crucial step for the next generation of energy solutions. Besides the energy savings upon synthesis, low temperature methods significantly enhance the capabilities of fine tuning of the structure and properties of a magnetic material. A recent example is an intercalation of Li-ammonia or Li-pyridine into interlayer space of FeSe superconductor, which leads to the significant increase of the superconducting transition temperature. Products of the Li-amines intercalation into pre-synthesized FeSe are fine powders with low degree of crystallinity. Temperatures of conventional solid state synthesis of FeSe (> 1000 K) are not compatible with organic amines. We have developed low temperature (T < 500 K) synthetic route to iron chalcogenides, FeQ (Q = S, Se, Te). The developed method allows us to modify crystal structure of layered FeQ chalcogenides by means of the intercalation of iron-amino complexes. Unlike traditional intercalation techniques, high quality single crystals were obtained, thus facilitating determination of the crystal structure and evaluation of the properties of the synthesized compounds. Synthesis of new materials, their crystal and electronic structure as well as magnetic properties will be discussed.

Our ability to design new materials with desired electrochemical, thermoelectric or strongly-correlated electron properties is limited by thermodynamic control over reaction products in traditional high-temperature synthetic procedures. On the contrary, topotactic reactions, where extensive parts of the original framework are retained, allow for greater control of the structure of the final products; therefore, a combination of desired structural features, spin and oxidation states can be produced in a final material in a predictable fashion.
A 'chimie douce' solvothermal reduction method was developed for topotactic oxygen deintercalation of complex metal oxides. The reduction of the Ruddlesden-Popper nickelate La₄Ni₃O₁₀ was used as a test case to prove the validity of the method. The completely reduced phase La₄Ni₃O₈ was produced via the solvothermal technique at 150°C - a lower temperature than by other more conventional solid state oxygen deintercalation methods. Unlike other techniques, a pure Ni¹⁺ compound, LaNiO₂, can be prepared by solvothermal reduction, demonstrating the advantages of the developed method for synthesis of highly metastable reduced compounds.
Metastable oxyfluorides SrFeO₂F and La₄Ni₃O₈F₂ were prepared through a low temperature, multistep synthesis via fluorination of the infinite layer intermediate phases. Influence of the synthetic pathway on O/F short range ordering and physical properties will be discussed. Mossbauer spectroscopy measurements revealed the predominance of cis fluorine configuration in FeO₄F₂ polyhedra, confirming a difference in local Fe coordination in comparison with O/F disordered SrFeO₂F.
When trying to achieve anion ordering during synthesis, it is important to perform anion intercalation at as low a temperature as possible to avoid thermal randomization of the anions. A low temperature solvothermal fluorination technique, which we developed, allows for fast and facile synthesis at lower temperatures than gas- solid fluorination by XeF₂.
In all known compounds with the alpha-NaFeO₂ structure transition metals oxidation states are either 3+ or 3+/4+. We have developed an “aliovalent exchange plus intercalation” multistep soft chemistry approach for the preparation of a series of new layered transition metal oxides. The synthetic procedure resulted in compounds with the alpha-NaFeO₂ type structures and, uniquely, with transition metals in mixed valent 2+/3+ oxidation states. The oxidation state in the final compounds can be controlled by utilizing A_xMO₂ precursor phase with different x. Crystal structures and physical properties of these novel compounds will be presented.

The structures of the metal-cyanide layers within the group 10 compounds Ni(CN)2, Pd(CN)2 and Pt(CN)2, which consist of vertex-sharing square-planar M(CN)4 units, have recently been determined in detail using total neutron diffraction and will be discussed. Moving to group 11, the binary cyanide, Cu(CN)2, is not known to exist. However, we show here that copper(II) can be stabilised in a cyanide-only environment in the stoichiometric, mixed copper-nickel cyanide, CuNi(CN)4, and in the solid-solution, Cu1-xNi1+x(CN)4 (½ le; x < 1).
The atomic structure of the layers in CuNi(CN)4 and the stacking relationship between nearest-neighbour layers have been determined from total neutron diffraction studies at 10 and 300 K. The structure consists of flat layers of perfectly square-planar [Ni(CN)4] and [Cu(NC)4] units linked by shared cyanide groups i.e. both the metal and cyanide groups are perfectly ordered with Cu(II) coordinated to the nitrogen end of the cyanide group and Ni(II) to the carbon end. It is rather unusual to find Cu(II) in a square-planar environment within an extended solid. The layered structure of this new mixed-metal cyanide is closely related to those of Ni(CN)2, which forms more extended sheets, and Pd(CN)2.xNH3 and Pt(CN)2.xH2O, which form as nanocrystalline materials.
The overall appearance of the powder X-ray diffraction pattern of CuNi(CN)4, including the unusual peak shapes of the observed Bragg reflections, has been successfully explained using models incorporating stacking disorder between next nearest neighbour layers. CuNi(CN)4 shows similar thermal expansion behaviour to that observed previously for Ni(CN)2 [1,4] with negative thermal expansion within the layers (αa = -9.7 MK-1) and positive thermal expansion between the layers (αc = +89 MK-1) measured over the temperature range 200-540 K.
The stability of Cu(II) atoms in a cyanide-only environment has been investigated by varying the ratio of the Cu2+ and Ni2+ ions used in the synthesis. Using a Cu:Ni ratio of 1:1, the anhydrous phase, CuNi(CN)4, is precipitated directly. For Cu:Ni ratios less than one, hydrates of the form Cu1-xNi1+x(CN)4.yH2O (½ le; x < 1; y le; 6) are produced which can be dehydrated to form the corresponding anhydrous compounds, Cu1-xNi1+x(CN)4. These compounds readily rehydrate. Replacement of Cu2+ by Ni2+, which occurs when the Cu:Ni ratio is less than one, leads to the creation of [Ni(NC)4] units. These in turn readily hydrate to form six-coordinated [Ni(NC)4(H2O)2] groups similar to those found in nickel-cyanide hydrates, such as Ni(CN)2.3H2O. [Ni(CN)4] units do not hydrate; hence CuNi(CN)4, which contains such units, is not found in a hydrated form. With Cu:Ni ratios above one, partial reduction of the Cu(II) occurs to form LT-CuCN, in addition to CuNi(CN)4. This result further confirms that Cu(II) ions can only be stabilised when connected to the nitrogen ends of bridging cyanide

The discovery of giant magnetocaloric effect (MCE) in rare-earth and transition metal based materials and prototype equipment development has sparked great interest for magnetic cooling technology. This has also made it a promising alternative to the current vapor compression technology. However, significant synthetic challenges for industrial scale production of MCE materials exist for the successful commercialization of this technology.
We have focused our research activities on the Mn_xFe_2minus;xP_ySi_1-y family of magnetocaloric materials which shows great promise due to their large magnetocaloric properties as a result of being first-order phase transition materials (Tegus et al. 2002, Thanh et al. 2008). Additionally, they exhibit tunable Curie temperatures and earth abundant constituent raw materials. Moreover, they possess excellent long-term stability and their ability to be formed into complex shapes. In this presentation, we will discuss some of the challenges encountered during the up-scaled production of these materials, and how these have been overcome using industrial synthetic routes (for e.g. meltspinning and atomization) in addition to more traditional academic ball milling approach. We will also discuss the magnetocaloric properties of the obtained materials and the performance of these materials during magnetocaloric cycling.
REFERENCES
Tegus, O.; Brück, E.; Buschow, K.; de Boer, F., Transition-metal-based magnetic refrigerants for room-temperature applications, Nature2002, 415, 150.
Thanh, D.; Brück, E.; Trung, N.; Klaasse, J.; Buschow, K.; Ou, Z.; Tegus, O.; Caron, L., Structure, magnetism and magnetocaloric properties of MnFeP1-xSix compounds, J. Appl. Phys.2008, 103, 07B318.

Accommodation of excess oxygen in CeO₂, ThO₂ and UO₂ has been investigated using ab-initio modelling. Hyperstoichiometry was preferentially accommodated by the formation of peroxide species in CeO₂, ThO₂ but not in UO₂, where oxygen interstitial defects are dominant. Migration of the excess oxygen defects was also studied; the peroxide ion in CeO₂ and ThO₂ is transported via a different mechanism to the oxygen interstitial in UO₂. Formation of Frenkel defects was investigated to understand the eect of a peroxide formation on the drive for defect recombination. The presence of the Frenkel vacancy in proximity to the associated additional oxygen defect induces the oxygen to take up an interstitial site, similar to excess oxygen defects in UO₂ rather than remain part of a peroxide molecule.

Mn-doped CeO2 electrolytes were prepared using a soft chemical technique which involved co-precipitation of Mn2+ and Ce4+ using oxalic acid as the precipitant. The incorporation of MnO into ceria lattice was found to be pH dependant. A wider solubility range of managanese dopant concentration into ceria lattice prepared via this method is highlighted. The resultant powders of Mn-doped CeO2 solid solutions, formulated as Ce1-xMnxO2-x, (0.05 le; x le; 0.25), were investigated thoroughly for the first time, from the aspect of synthesis where pH was precisely controlled and varied from 5 - 11. The optimized pH for a stable incorporation of Mn dopant into ceria was found to be pH = 10, in order to obtain the correct stoichiometric compound. The solubility limit of MnO in the CeO2 fluorite lattice structure was suggested to be x = 0.20. The phase composition, morphology properties and elemental analysis of the oxalate and derived-powder was characterized using X-ray diffraction, DTA/TG, SEM and X-ray fluorescence (XRF) respectively. The grain size decreases with increase of MnO content. The electrical conductivity of sintered samples of Mn-doped CeO2 ceramics were investigated in air as a function at 473 - 1073 K using AC impedance spectroscopy. The contributions of the bulk (grain interior), the grain boundary and the electrode polarization behaviour are well documented. The bulk conductivities of the Mn-doped CeO2 ceramics sintered at 1473 K at a test temperature of 1073 K were determined to be 4.223 x 10-4 S cm-1 for Mn content x = 0.10 with activation energy, Ea = 0.88 eV.

Magnetic ceramic nanoparticles of the type xIn2O3-(1-x)alpha-Fe2O3, xV2O5-(1-x)alpha-Fe2O3 and xZnO-(1-x)alpha-Fe2O3 (x=0.1-0.7) were synthesized from the mixed oxides using mechanochemical activation for 0-12 hours. X-ray diffraction was used to derive the phase content, lattice constants and particle size information as function of ball milling time. Mossbauer spectroscopy results correlated with In3+, V5+ and Zn2+ substitution of Fe3+ in the hematite lattice. SEM/EDS measurements revealed that the mechanochemical activation by ball milling produced systems with a wide range of particle size distribution, from nanometer particles to micrometer agglomerates, but with a uniform distribution of the elements. Simultaneous DSC-TGA investigations up to 800 degrees C provided information on the heat flow, weight loss and the enthalpy of transformation in the systems under investigation. This study demonstrates the formation of a nanostructured solid solution for the indium oxide, an iron vanadate (FeVO4) for the vanadium oxide, and of the zinc ferrite (ZnFe2O4) for the zinc oxide. The transformation pathway for each case can be related to the oxidation state of the metallic specie of the oxide used in connection with hematite.
NSF-DMR-0854794

Metal-Organic Frameworks (MOFs) have gained a tremendous amount of attention in the past few decades. Due to the tunable nature of their ligand geometry, their enormous surface area and their large gas uptake capacities, MOFs are widely applied in many areas such as gas storage, gas separation, CO2 capture, catalysis, drug delivery, sensors, photosensitive materials and magnetic materials. However; it is still problematic to construct MOFs with large porosity, high stability and good crystal quality, while many potential MOF applications require them to possess those properties simultaneously. Typically, in order to attain larger pore sizes and surface areas, researchers attempt elongation of MOF constructional units. However, this will often inherently undermine the framework stability and crystallinity and increase the possibility of framework interpenetration. Additionally, recent research indicates that the crystal size, quality and morphology can largely affect the surface area of the resulting MOFs.
The MOFs based on the ultrastable zirconium polyoxo clusters have demonstrated their excellent stability toward air, water, or even concentrated acid. Even though a limited number of Zr MOFs were published, many of them suffer from a low crystallinity and limited pore sizes. In this work, a series of non-interpenetrated zirconium MOFs were synthesized from a group of tetrahedral ligands via a modulated synthesis strategy. All of them possess new MOF topologies, large cavities and high crystal quality. Two categories of polymorphic MOFs can be identified and their isostructural MOFs were obtained by using elongated analogous ligands. Remarkably, PCN-525 has largest surface area, pore size (up to 25Å) and solvent accessible volume (up to 84.10%) among all the MOFs constructed from tetrahedral ligands. It is one of the rare examples of mesoporous Zr MOFs with three dimensional channels. PCN-522 is the first MOF that contains two distinctive Zr-based clusters, which has an unprecedented 4, 12, 12-connected topology that incorporates tetrahedra, cuboctahedra and icosahedra in the same network. This work provides both insights into novel framework topologies with tetrahedral building units and a practical method of constructing MOFs with large pore size and high stability.

Multifunctional materials combine more than one imaging modality such as optical imaging, X-ray computed tomography (CT), positron emission tomography (PET), and magnetic resonance (MR) imaging contained in single vehicle. In particular, optical imaging provides its high resolution in bio-imaging and MR imaging offers excellent anatomical depth, non-invasive, and real time monitoring. Thus, a lot of attentions had been paid to the development for the multifunctional nanomaterials combining the two representative modalities such as optical and MR imaging, especially for application in biomedical applications.
It is worth noting that lanthanide-doped (Ln3+) nanoparticles serves as an alternative to conventional luminescent labels such as organic dye, QDs for application in biological medical imaging due to its advantageous characteristics such as low toxicity, high resistance to photo-bleaching and photochemical degradation. Moreover, the luminescence features of lanthanide ions also include high quantum yield, large stoke shift, abundant energy level transitions, narrow emission band width, and long fluorescent life time.
In recent, Gd3+-based inorganic nanomaterials has attracted much interest because they could be used as potential multifunctional platform. It was well known that a paramagnetic nature of Gd3+ ion arising from seven unpaired electrons in 4f electron shell could be utilized as contrast agents for T1-enhanced MR imaging owing to their enhancement of relaxation of the neighboring protons. In addition, by doping light-emitting various lanthanide ions (Ln3+) into a Gd3+-containing host matrix, novel materials possessing both advantages of fluorescent and magnetic properties could be achievable for multimodal imaging. For the research of optical imaging on the multifunctional GdPO4 nanoparticles, the research has been extensively studied only in visible range. There have been no reports on multifunctional GdPO4 nanoparticles having both UV emission and MR properties, which could be potentially used as alternative multifunctional nanoprobes. The understanding of optical properties of Ce3+, Pr3+ and Gd3+, having electronic configuration in UV spectral domain in inorganic compounds is of great important due to the potential technological applications as imaging, lithography, and optical data recording. Thus, nanoparticles with both UV emission and magnetic resonance properties could open new area of biomedical technology.
In this report, we present a general strategy for the synthesis of GdPO4 nanorods and nanoparticles doped with Ln3+ (Ln3+ = Ce3+, Pr3+) having strong UV emission and magnetic property. We explain multifunctional property change when crystal phase and structure change from hexagonal GdPO4 nanorods to monoclinic GdPO4 nanoparticle after calcination at 900 degrees Celcius , which could be potentially applied as MR imaging contrast agent.

Thermochromic smart film, typically based on VO2 nanoparticles, has received particular interest because it can intelligently modulate the amount of near-infrared ray by changing from transparent state at low temperature to reflective state at high temperature, while maintaining visible transmittance. This film is promising for application in building and automotive glasses to increase energy efficiency.
In this study, we demonstrated that hydrothermal process used to prepare metal-doped VO2(M) nanopowder with a special emphasis on calcination condition and novel solution process used to prepare transparent, stable and flexible VO2(M) based film. Monoclinic VO2(M) nanopowder was obtained from vanadium pentoxide and oxalic acid by controlling hydrothermal and calcination conditions. By further increasing calcinations temperature to about 700°C for 2 h with N2 gas during calcinations step, VO2(A) was transformed only to VO2(M). Due to the small band gap between VO2(A) and rutile-type VO2(M), VO2(A) would directly be transferred to stable VO2(M). Metal doping led to decrease phase-transition temperature from 68°C to 35°C. Metal-doped VO2(M) nanoparticles based film could exhibit a large change of NIR transmittance for phase-transition temperature than bare VO2 based film.

The structure refinement of three decagonal phases: Al-Cu-Co, Al-Cu-Rh, Al-Cu-Ir will be presented [1]. The synchrotron diffraction experiments were performed at the Swiss - Norwegian beam line at ESRF, Grenoble, France. All three decagonal phases show ~4 Å periodicity (two atomic layers per period). A computer program SUPERFLIP [2], based on the charge-flipping algorithm, was used for the initial phasing of the data and obtaining the electron density maps. These maps were used for deriving a Rhombic Penrose Tiling (RPT) model with a tiling edge-length of ~17 Å. The decoration of the unit tiles is based on the ~33 Å cluster proposed by Hiraga & Oshuna [3]. The decoration of RPT with Hiraga clusters is such, that the cluster centers form the Pentagonal Penrose Tiling of an edge-length of ~20 Å. The Hiraga cluster can be considered as a supercluster built of 5 clusters proposed by Deloudi et al. [4]. Such a structure explains well the strong Patterson peaks of ~ 12 Å, ~20 Å, and ~32 Å occurring for all three phases. The structure refinement was performed in the real space using the so-called Average Unit Cell approach. This method allows a purely 3D optimization of a quasicrystalline structure and has been previously used for a variety of decagonal pahses in the Al-Ni-Co system [5-7]. Our work shows the first solution of a quasicrystal as a ternary alloy (Rh and Ir phases). The final R-values are reasonable, the structure is consistent with TEM images and the chemical composition agrees well with the EDX measurements.
References
[1] P. Kuczera, J. Wolny, W. Steurer, Acta Crystallogr. B 68 (2012) 578.
[2] L. Palatinus, G. Chapuis, J. Appl. Crystallogr. 40 (2007), 786.
[2] K. Hiraga, T. Ohsuna, K.T. Park, Phil. Mag. Lett. 81 (2001), 117.
[4] S. Deloudi, F. Fleischer, W. Steurer, Acta. Crystallogr. B 67 (2011), 1.
[5] P. Kuczera, J. Wolny, F. Fleischer, W. Steurer, Philos. Mag. 91 (2011), 2500.
[6] P. Kuczera, B. Kozakowski, J. Wolny, W. Steurer, J. Phys. Conf. Ser. 226 (2010), 012001.
[7] J. Wolny, B. Kozakowski, P. Kuczera, H. Takakura, Z. Kristallogr. 223 (2008), 847.

A piezoelectric ceramic Pb(Ti_1-xZr_x)O₃ (PZT) is widely used for various applications such as transducer and sensors. PZT shows a maximum piezoelectric property at composition around x = 0.5, the boundary separating the tetragonal (Ti-rich) and the rhombohedral (Zr-rich) phases in the phase diagram. This boundary is known as a morphotropic phase boundary (MPB). The origin of the enhanced piezoelectric property at MPB is explained as follows. There exist a monoclinic phase with a radic;2a × radic;2a × a unit cell where a was the cubic perovskite lattice parameter, and Cm symmetry at MPB composition at low temperature. The lack of symmetry axis in the monoclinic structure allows the rotation of the ferroelectric polarization vector between the polar axes of the tetragonal and the rhombohedral phases. Such a polarization rotation is induced by application of electric filed leading to the enhancement of the piezoelectric constant. However, the polarization rotation has never been observed experimentally.
In this study, we show the presence of polarization rotation in BiCo_1-xFe_xO₃ (x ~ 0.7). BiCoO₃-BiFeO₃ system attracts attention as a candidate lead-free piezoelectric material because of the similarity of the phase diagram to that of PZT. The crystal structure as determined by powder synchrotron X-ray diffraction (SXRD) was the same as that of the low temperature phase of PZT at the MPB. Composition and temperature induced second order structural transition from tetragonal to monoclinic structures was observed. The structural change was accompanied by a rotation of the polarization vector from [001] to [111] directions of a pseudo cubic cell. This is the first observation of the polarization rotation in a monoclinic perovskite.

PbCrO3 had long been considered as a boring antiferromagnetic cubic perovskite. However, the lattice constant of 4.01Å is considerably larger than that of Sr2+Cr4+O3 and Cr3+ is expected from bond valence sum. Furthermore, pressure induced volume collapse of 9% was recently found[1]. To clarify its mysterious nature we prepared pure PbCrO3 and Pb1-xSrxCrO3 samples, and systemically studied their physical properties. The temperature dependence of paramagnetic susceptibility indicated that the actual valence of Cr is +3 for pure PbCrO3, contrarily to +4 for Cr of the previous reports [2]. Meanwhile a pressure induced insulator to metal phase transition was observed for PbCrO3 around 3GPa, which should be attributed to the electronic configuration change of Cr from t2g3 to t2g2. We thus proposed a new oxidation state of Pb2+0.5Pb4+0.5CrO3 like Bi3+0.5Bi5+0.5NiO3 [3] with disordered arrangement of Pb2+ and Pb4+ which was confirmed by X-ray photoelectron spectroscopy (XPS). An intermetallic charge transfer between Pb4+ and Cr3+ leads to the Pb2+Cr4+O3 state under pressure. A distinct volume drop was found for Pb1-xSrxCrO3 at around x=0.3 where insulator to metal phase transition was also observed, suggesting the valence change of Cr ion from 3+ to 4+ which was confirmed by O-K edge X-ray absorption spectroscopy(XAS). Based on the above results we believe that charge transfer between Pb and Cr takes place in both PbCrO3 and Pb1-xSrxCrO3 under pressure and by Sr substitution, respectively.
[1] W. Xiao et al., PNAS 107, 14026 (2010).
[2] A. M. Arévalo-Loacute;pez et al., Inorg. Chem. 48, 5434 (2009).
[3] M. Azuma et al., Nat. Commun. 2, 347 (2011).

Materials with the CuFeO2 structure are of great interest as transparent conducting oxides [1] and for their exotic magnetism. This layered structure consists of sheets of edge-sharing metal-oxygen octahedra separated by group IB metals with a dumbbell coordination. Two stacking polytypes are commonly found - the 3R and 2H - and often samples contain a mixture of the two, making the interpretation of the properties difficult.[1]
A variation of the CuFeO2 structure is found in some cases where two different B cations form an ordered honeycomb lattice in the sheets of edge-sharing octahedra. The honeycomb lattice is of interest to the magnetism community as a frustrated X-Y system, and as a spin-liquid candidate when strong spin-orbit coupling is present, such as in Na2IrO3.[2]
Here we describe our results on the 2H polytypes of Cu3Ni2SbO6 and Cu3Co2SbO6 formed by a high temperature synthesis route.[3] Synchrotron powder X-ray diffraction, neutron powder diffraction data and high resolution transmission electron microscopy are used to resolve atomic and magnetic structures of the materials. In addition, synthesis of the 3R polytypes has been accomplished by low temperature cation exchange. Their structures and properties will be compared to the 2H polytypes.
[1] M.A. Marquardt, N.A. Ashmore, D.P. Cann, Thin Solid Films 496 (2006) 146-156.
[2] Y. Singh, P. Gegenwart, Physical Review B 82 (2010) 064412.
[3] J.H. Roudebush, N.H. Andersen, R. Ramlau, V.O. Garlea, R. Toft-Petersen, P. Norby, R. Schneider, J.N. Hay, R.J. Cava, Inorganic Chemistry (2013).

Lanthanum germanate and silicate (La9.33+x(MO4)6O2+1.5x, M=Ge or Si) with an apatite-type crystal structure are promising oxide-ion conductors for electrolytes of solid oxide fuel cells. It was reported that mobile interstitial oxide ions are introduced in the case of x > 0 with increasing ionic conductivity, and it is thus important to understand its oxide-ion conduction mechanism on an atomic level. For this purpose, the conduction mechanisms in lanthanum germanate and silicate have theoretically been investigated in the present study. Specifically, the stable sites of interstitial oxide ions in the crystals and the potential barriers of conduction pathways connecting the stable sites were clarified in a first-principles manner based on the projector augmented wave method.
Regarding the obtained stable sites of interstitial oxide ions, they are located between neighboring two GeO4 tetrahedra in lanthanum germanate. On the other hand, in lanthanum silicate, the similar sites between SiO4 tetrahedra are metastable sites, and the most stable sites are located at the periphery of the O4 column. During the oxide-ion conduction, cooperative migration processes involving several oxide ions at interstitial and neighboring regular sites, i.e., the interstitialcy mechanisms, predominantly occur in these two systems, rather than the simple interstitial mechanisms. In lanthanum germanate, cooperative oxide-ion conduction processes around GeO4 tetrahedra along the c axis are dominant for the long-range migration. On the other hand, in lanthanum silicate, the estimated potential barrier of the cooperative conduction in the O4 column along the c axis was less than 0.1 eV, which is much lower than the apparent activation energy reported experimentally (0.4-0.9 eV). This is probably because the interactions between interstitial oxide ions closely-arranged along the c axis in the O4 column are not taken into consideration. This implies the migration processes between the most stable and metastable sites should be the key to determine the conductivity curve in the silicate. Thus, there is the significant difference in oxide-ion conduction mechanism between the two systems, which reflects the difference in the stable sites despite the same apatite-type crystal structure.

Many classes of proton-conducting oxides have been reported so far, e.g., perovskite-type, fluorite-type, pyrochlore-type, monazite-type, and their related oxides. According to the conventional view, protons in such the oxides reside and rotate around oxide ions with OH bonds and sometimes hop into neighboring oxide ions (rotations and hoppings). Geometries of oxygen polyhedra in the crystals are, therefore, key factors in the proton conductivities. In the present study, we have theoretically analyzed proton conduction mechanisms in several types of oxides from first principles, to clarify the roles of the oxygen polyhedral network in the crystals.
All the first-principles calculations were based on the projector augmented wave method implemented in the VASP code. Local energy minima in the crystals (proton sites) were determined by construction of the potential energy surfaces of a proton with the fixed atomic positions and the subsequent structural optimizations. Proton conduction paths were evaluated using the nudged elastic band method, and the kinetic Monte Carlo simulations were finally performed to estimate the proton diffusivity and conductivity.
First, concerning the proton sites in oxides, protons were found to prefer non-shared oxide ions to corner-shared oxide ions in oxides to form an OH bond. This trend appears prominently in oxides having lower-coordinated oxygen polyhedra, which implies that the positive charges of cations at the centers of polyhedra not perfectly screened by coordinated oxide ions lead to the comparatively high potential energy in the vicinity of corner-shared oxide ions with two neighboring cations. Thus, corner-shared oxide ions seem to have no direct contribution to the proton conduction in oxides.
Note here that protons are further stabilized by hydrogen bonds (OH-O bonds) formation in addition to the OH bonds. The distances from the second-nearest-neighbor (2NN) oxide ions are also short (< 1.7 Å), which are comparable to those in ice and water. In other words, proton incorporation in oxides can be rephrased as hydrogen bond formation. Furthermore, proton conduction in oxides can be regarded as repetition of forming and breaking the hydrogen bond, i.e., hydrogen bond switching, which is a new picture of proton conduction in oxides in place of rotations and hoppings. Corner-shared oxide ions are involved in the hydrogen bond formation and switching as the 2NN oxide ions, and not directly but indirectly contribute the proton conduction in oxides. In addition, the corner-sharing of oxygen polyhedra plays a role in reducing the distances among non-shared oxide ions, which can provide fast proton migration paths in the connection direction. Actually, the present study found fast proton conduction channels along infinite oxygen polyhedral chains in La₃NbO₇ and LaP₃O₉, leading to their large anisotropic proton diffusivities and conductivities.

The solid-state reaction of thin film metals on germanium substrates is used to form low sheet resistance germanide layers and low resistance contacts for germanium semiconductor devices, similar to the formation and use of silicides in silicon devices. Nickel germanide is the most promising germanide for use in germanium contacts because it has low resistivity (15mu;Omega;.cm) and low temperature of formation. In this study we examine the thermal budget, investigating the lowest temperature of formation that can be used. Results show that temperatures less than 300 C can be used to form NiGe but temperature duration is significantly longer than for higher temperatures. At temperatures less than 200 C, NiGe does not form.
X-Ray Photoelectron Spectroscopy and X-Ray Diffraction were used to examine the stoichiometry and structure of the germanides formed and cross-section Transmission Electron Microscopy was used to show the texture of the germanide layer and in particular the texture and constituent atoms of the germanide to germanium interface. These results show that the germanide formed is very close to NiGe (1:1), the surface roughness (approximately 4nm) is only slightly greater than the polished Ge wafer, grain sizes approximately 100nm in dimension and the roughness of the NiGe to Ge interface is significantly high at approximately 30nm. As suggested by the interface roughness, the grain heights for the formed NiGe grains varies from approximately 1.9 times to 2.4 times the original Ni thickness. Oxygen contamination is evident at the germanide-germanium interface using TEM element mapping, but does not occur in the germanide material. The roughness of the germanide-germanium intercface was determined by selective etching of the germanide and using an atomic force microscope to determine the roughness of the exposed germanium surface.
The electrical properties of the germanides formed were determined using the Van der Pauw technique and using a novel test structure to determine the interface specific contact resistance between the NiGe and germanium substrate.
The solid state reactions were done on a resistive heat stage in a nitrogen environment. Completion of reaction for the Ni thicknesses used (50 nm to 500nm) was determined using XRD and sheet resistance measurements. The solid state reaction was also examined using a heat stage with situ XRD taking measurements.

Antimony oxides are widely used as oxidation catalysts, optoelectronic, and magnetic materials[1]. Its amorphous phase has also been attracting much attention due to its potential use in advanced optical devices[2]. Antimony oxides come in a wide range of stoichiometry and polymorphs, namely α-Sb₂O₃, β-Sb₂O₃, γ-Sb₂O₃, α-SbO₂, β-SbO₂ and Sb₂O₅, arising from the existence of various possible oxidation states of antimony. There have been rigorous efforts to synthesize and characterize these oxide phases[3], however, currently the microscopic fundamental understanding is still lacking. This is especially so for the local ordering of its amorphous phase. In this work, we employ first-principles based density-functional theory calculations and ab-initio molecular dynamics to study the crystalline and amorphous phase of these oxide polymorphs, detailing their energetics, atomic, and electronic structure. This preliminary study provides a platform for our future work on studying the use of antimony oxide nanostructures in advanced coatings and optical devices.
[1] H. S. Chin, K. Y. Cheong, and K. A. Razak, J. Mater. Sci. 45, 5993 (2010).
[2] K. Terashima, T. Hashimoto, T. Uchino, S.-H. Kim, and T. Yoko, J. Ceram. Soc. Jpn.104, 1011 (1996).
[3] D. Orosel, R. E. Dinnebier, V. A. Blatov, and M. Jansen, Acta Crystallogr. B68, 1 (2012)

CuCr2Se4 is a room temperature ferromagnet and metallic conductor [1-2]. It crystallizes in spinel type structure, the space group Fd m with lattice parameter a = 1.03340 nm [3] and has a normal cation distribution. The copper ions occupy tetrahedral Wyckoff site 8a and the chromium ions trigonal antiprismatic (usually called octahedral) site 16d. The ease of doping, usually in a large concentration range, has already been exploited for renewable energy [4].
CuCr2Se4 single crystals doped with ytterbium were obtained using chemical vapour transport method. Binary selenides CuSe and Yb2Se3 were used as the starting materials and anhydrous chromium chloride CrCl3 was a transporting agent. The crystallization process was carried out in quartz ampoules and in horizontal temperature zonal furnace. The weighs were prepared with the assumption that ytterbium would substitute chromium, according to the reaction:
(4-2.25) CuSe + 0.75 Yb2Se3 + (2-x) CrCl3 → Cu[Cr2-xYbx]Se4 + CuCl2 + YbCl3 for x=0.1; 0.25, 0.5. The well-shaped octahedral single crystals were chosen for further investigations. First chemical composition was determined using energy-dispersive X-ray fluorescence spectrometer (EDXRF). It was established that amount of ytterbium admixture is about half of weight percentage.
Dynamic (ac) magnetic susceptibility was measured in the temperature range 4.2-300 K and at an internal oscillating magnetic field Hac = 3.9 Oe with an internal frequency f = 300 Hz. Magnetization was measured in the magnetic field Hdc = 0.5, 1.0, 5.0 and 10.0 kOe and recorded both in zero-field-cooled (ZFC) and field-cooled (FC) mode. Magnetization isotherms were measured at 4.2 K and at 300 K in the static magnetic field up to 70 kOe. For that purposes a Quantum Design System (MPMS XL) was used. Static (dc) magnetic susceptibility was measured using a Faraday type Cahn RG automatic electrobalance up to 600 K. The most spectacular observation is that for small amount of chromium and ytterbium both the real and imaginary components of the magnetic susceptibility are oscillating around the value zero and the FC-ZFC splitting suggests the diamagnetic frustration while for larger Cr and Yb-content a ferrimagnetic state occurs.
Acknowledgements
This paper is funded from science resources for years 2011-2014 as a research project (project No. N N204 151940).
[1] G.J. Synder, T. Caillat, and J.P. Fleurial, Mat. Res. Inn. 67, 5 (2001).
[2] A. Payer, R. Schoellhorn, C. Ritter, and W. Paulus, J. All. Comp. 191, 37 (1993) .
[3] I. Okonska-Kozlowska, J. Kopyczok, H.D. Lutz, and Th. Stingl, Acta Cryst. C49, 448 (1993).
[4] G.J. Synder, T. Caillat, and J.P. Fleurial, Phys. Rev. B 62, 10185 (2000).

Spontaneous polarization enhancement or stable ferroelectric phases in incipient ferroelectrics have been theoretically predicted for nanowires and nanoparticles [1,2]. In this work, the possibility of nanosize induced ferroelecticity in CaTiO3 nanocrystals is studied by using second harmonic (SH) generation, photoluminescence and Raman spectroscopy as a function of temperature. The CaTiO3 nanoparticles (40nm to 50nm size) were grown by solid-state reaction [3] and sol-gel techniques [4] and verified the single-phase composition by XRD and TEM.
Experimental evidence of nanosize induced symmetry lowering in CaTiO3 perovskite nanocrystals are reported. More specifically, we show how the generated SH response from CaTiO3 nanocrystals vanishes upon heating at around 380 K and recovers when the system is cooled down. Thus, even though the lack of inversion symmetry required for SHG may be relaxed at nanoparticle surfaces, the presence of a well-defined Tc indicates that the system undergoes through a structural transition involving a symmetry reduction (non-centrosymmetric) in the crystal structure. This transition is confirmed by Raman spectroscopy, as manifested by the softening observed for low frequency modes at similar temperatures. Density Functional Theory (DFT) and empirical potential modeling shows a surface reconstruction and suppression of octahedral rotations as the origin of this ferroelectric behavior.
[1] S. Li and K. Rabe, Am. Phys. Soc, APS March Meeting. Abstract # S.20.011 (2007)
[2] A. N. Morozovska et al. Phys. Rev. B, 76, 014102 (2007)
[3] J. Li et. al., Mat. Lett, 65, 1556-1558 (2011)
[4] K. Lemanski et. al., J. Sol. State Chem., 184, 10 (2011)

The normal spinel ZnCr2Se4 (SG 227, a=10.489Å) is a semiconductor with high positive paramagnetic Curie-Weiss temperature (115 K), which orders magnetically at 21K into a spiral structure. The magnetism is governed by the balance between ferromagnetic Cr-Se-Cr superexchange and numerous next neighbor antiferromagnetic interactions, which are relatively easy tuned by doping. Numerous useful properties can be generated by a proper selection of dopant like colossal magnetoresistance or increased Seebeck effect. Of a special interest is doping with 4f metals due to their high localized magnetic moment.
Our investigations aim to describe how the introduction of dysprosium and neodymium changes the basis properties of the matrix.
The polycrystalline compounds ZnCr1.95Dy0.05Se4 and ZnCr1.95Nd0.05Se4 were prepared by ceramic method according to chemical reactions:
ZnSe + 0.975Cr2Se3 + 0.25Dy2Se3 = ZnCr1.95Dy0.05Se4 (1)
ZnSe + 0.975Cr2Se3 + 0.25Nd2Se3 = ZnCr1.95Nd0.05Se4 (2)
The stoichiometric quantities of binary selenides were sintered twice in silica ampoules for 240h at 1173K. The XRD phase analysis revealed a single spinel phase (space group Fd-3m) up to the detection limit of the method and structural parameters obtained using the Rietveld method.
The chemical compositions of ZnCr1.95Dy0.05Se4 and ZnCr1.95Nd0.05Se4 compounds were measured using scanning electron microscopy. The magnetic properties were determined using high magnetic stationary fields (up to 14 T) and SQUID - magnetometer (0.05 T) in the temperature range 2-300 K and are presented below.
Chemical composition, structural parameters and magnetic properties for ZnCr1.95Dy0.05Se4 and ZnCr1.95Nd0.05Se4 compounds in comparison to the ZnCr2Se4:
Nominal composition: ZnCr1.95Dy0.05Se4, Chemical composition: Zn0.92Cr1.68Dy0.06Se4, a=10.4970(4)A, u=0.25967(5), mu;eff (B.M./f.u.)=5.17, mu;sat(B.M./f.u.)=6.24, ΘCW(K)=66.5, CM(K)=3.34, TN(K)=21.7.
Nominal composition : ZnCr1.95Nd0.05Se4, Chemical composition: Zn0.90Cr1.87Nd0.07Se4.0,
a=10.4978(7)A, u =0.25952(8), mu;eff (B.M./f.u.)=6.73, mu;sat (B.M./f.u.)=6.05, ΘCW(K)=56.4, CM(K)=5.65, TN(K)=25.3.
ZnCr2Se4: a=10.489(7)A, u=0.258, mu;eff (B.M./f.u.) =5.47, mu;sat (B.M./f.u.)=5.74, ΘCW(K)=115, CM(K)=3.54, TN(K)=21.
(a - lattice parameter, u - coordinate of Se)
Neutron powder diffraction of the Nd doped sample confirmed the presence of incommensurate spiral structure with propagation wektor k=0.4715(2) and magnetic moment on B site equal 2.91(3) mu;B.
The local structure around the dopants were analyzed using XANES studies. The results of investigations will be presented on the conference.
Acknowledgement
This study is funded from science resources for years 2011-2014 as a research project (project No. N N204 151940).

Ce³⁺ is known to show broad optical emission peaking in the green spectral range [1]. For the stabilization of 3-valent cerium in ceramic phosphors such as calcium scandate CaSc₂O₄, often codoping with sodium for charge compensation is performed (Na⁺, Ce³⁺ harr; 2 Ca²⁺). At the melting point of CaSc₂O₄ (asymp;2100°C), however, alkaline oxides evaporate completely and codoping is thus no option for crystal growth from the melt. It was shown recently [2] that even without codoping Ce³⁺:CaSc₂O₄ crystal fibers can be grown from the melt by laser heated pedestal growth (LHPG) in a suitable reactive atmosphere. Reactive means here that the oxygen partial pressure is a function of temperature and p_O2(T) rises for this atmosphere in such a way that Ce³⁺ is kept stable for all T. Crystal fibers with asymp;1 mm diameter and le;50 mm length were grown and characterized. Besides, fibers could be grown by micro-pulling-down (µ-PD).
Differential thermal analysis (DTA) was performed in the pseudo-binary system CaO-Sc₂O₃, and the specific heat capacity c_p(T) of CaSc₂O₄ was measured up to 1240 K by differential scanning calorimetry (DSC). Near and beyond the melting point of cerium scandate significant evaporation of calcium tends to shift the melt composition towards the Sc₂O₃ side - an effect that was observed already during crystal growth. Measurements and thermodynamic calculations reveal quantitative data on the fugacities of evaporating species.
[1] Y. Shimomura, T. Kurushima, N. Kijima, J. Electrochem. Soc. 154 (2007) J234.
[2] J. Philippen, C. Guguschev, R. Bertram, D. Klimm, J. Crystal Growth 363 (2013) 270.

Electronic conductivity in wide gap materials is an important component of many technologies, such as scintillators, photo-catalysts, and photovoltaics. Amorphous materials are cheaper to produce than single crystals and are often unavoidable at interfaces, but the conductivity suffers compared to the crystalline material. The composition and local structure in the glass affect the electronic structure and thus conductivity. We use a suite of simulation techniques to develop glasses with a range of local disorder (defects) and determine the correlation between local structure and electronic structure, with the aim of removing the localized states at the band edges and controlling electronic transport.
The recent availability of supercomputers with thousands of cores and efficient first-principles codes allows us to simultaneously model the long-range disorder of glasses and their electronic structure. Not only can the effect of the glass composition on electronic structure be investigated, but also the glass processing can be probed using simulated annealing. This comprehensive method of studying amorphous materials will inform synthesis efforts to improve conductivity.

A series of new metal chalcogenides were synthesized using KBr flux at 800 oC. The three compounds are isostructural and adopt the noncentrosymmetric space group belonging to the -43m crystal class. The MS4 tetrahedra form the oriented infinite columns running along the [111] direction in the three-dimensional framework that may account the occurrence of high SHG response. These compounds are transparent in the mid-infrared range and have the absorption edges between 1.59 eV and 2.26 eV. The new non-linear optical (NLO) materials are type-I non-phase matching and display strong SHG intensities larger than that of AgGaSe2. Raman spectroscopic characterization of the compounds is reported.

In this study, we investigated VO₂ particle property and coating method, affecting thermochromic property of VO₂ based film. Monoclinic VO₂ powder was obtained from vanadium pentoxide by controlling surfactant, hydrothermal pressure and filling ratio through hydrothermal process. By further increasing filling ratio, A-phase VO₂ powder was transformed to monoclinic VO₂ powder (VO₂(M)). The particle size of VO₂(M) was controlled well by the change of pulverizing condition during pulverizing process. VO₂ based film was fabricated by dispersion solution coating process on various particle size of VO₂(M). Thermochromic effect in VO₂ based film was increased with high transparency on decreasing the particle size of VO₂(M). The particle size of less than 40nm had excellent NIR switching efficiency. The optical properties, crystallinity, elemental composition and morphology of VO₂ powder were characterized by XRD, SEM, TEM, DSC, EDS and UV-vis-NIR.

Among the application-relevant materials class of mixed ionic-electronic conducting perovskite oxides (ABO₃), Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ (BSCF) exhibits an outstanding oxygen permeation, resulting from its superior ionic and electronic transport properties. These qualities identify BSCF as a very promising candidate for high-temperature membranes to produce pure oxygen in a very efficient manner.
However, in the targeted temperature range for applications (between 700 °C and 900 °C) the cubic BSCF phase, which is responsible for the excellent oxygen permeation properties, is not long-term stable below 840 °C and undergoes a phase transformation to hexagonal phase. Previous studies in literature suggest the possibility of stabilizing the cubic phase of BSCF in the aforementioned temperature range by B-site co-doping (at levels of 1 to 10 mol-%) with Y or Zr, respectively.
This paper is focused on the influence of Y and Zr co-doping on the electrical performance of the BSCF matrix. To this end, single-phase co-doped BSCF powders prepared by mixed-oxide route were used to sinter ceramic bulk samples.
For electrical characterization the effect of co-doping on the sintering behavior was studied in order to reduce sample porosity to a minimum. In this way, very dense bulk samples could be obtained that were electrically contacted by sputtered Pt contacts in 4-wire technique. These optimized dense ceramic samples were electrically characterized at temperatures between 700hellip;900 °C and oxygen partial pressures of 10 ^-5hellip;1 bar, enabling a direct comparison of electrical properties between the different compositions. Additionally, long-term electrical measurements at 800 °C in air shed light on the cubic phase stability of co-doped BSCF under operating conditions.

SiC is well-known to exhibit the polytypes more than 260 which were derived from the stacking order. Many of the polytypes have been characterized with spectroscopy. Amorphous SiC has been also investigated in a form of film synthesized through gas phase reaction. In this work, we describe the powder synthesis of a new type of SiC with the stacking disordered structure (SD-SiC) and the spectroscopic features. The Raman spectrum of SD-SiC was quite different from the other polytypes and was similar to the amorphous SiC. Nano-metric SiC powder with the stacking disordered structure was synthesized by high energy ball milling from elemental powders of Si and C under Ar atmosphere. The disordered SiC structure was characterized by 13C-, 29Si-NMR, IR, Raman, and XPS spectra. The kinetics of ordering of the disordered SiC will be also described.

Ba0.70Sr0.30TiO3 (BST-70/30) and Ba0.30Sr0.70TiO3 (BST-30/70) ceramics powder mixed with BaO-B2O3-ZnO glass powders were prepared via solid state reaction. The effects of glass contents on the dielectric properties, ferroelectric, and energy storage properties of BST ceramics were investigated. The ceramic materials were prepared using high energy ball milling for 4 hrs at 400 rpm. The milled powders were calcined at 1250C/10 hrs. Ceramic pellets (BST) were prepared using hydraulic press and sintered at 1500C/4 hrs. Glass compositions mentioned above were mixed with ceramic powders and milled for 2hrs. Glass-ceramic pellets sintered at 900°C/4hrs. XRD studies of the sintered pellets revealed the pure perovskite crystal structure. The crystal structure was further confirmed by SEM analysis. The SEM revealed monolithic grain growth. Initial studies revealed dielectric breakdown strength of 224kV/cm was achieved for BST ceramics with 20-wt% glass addition. In order to investigate the mechanism of dielectric breakdown performance, the relationship between dielectric breakdown strength and grain boundary barrier was studied by the measurements of breakdown strength and activation energy. The compositional variation on the phase transition temperature, dielectric constant, and ferroelectric to paraelectric phase transitions and energy storage densities are discussed.

Oxide-supported Ni_2-xM_xP nanocrystals (M = Fe, Co) are promising next-generation hydrodesulfurization (HDS) catalysts with the potential to address increasingly stringent regulations on allowable sulfur emissions that cannot be addressed by conventional sulfided molydbendum-based materials. Metal phosphide catalysts are typically prepared by temperature-programmed-reduction (TPR) of phosphates supported on silica, resulting in samples that are inhomogeneous in size and composition. Here we describe the synthesis of low-polydispersity Ni_2-xM_xP (M = Fe, Co) nanocrystals by arrested precipitation reactions. Phase-pure samples can be achieved over virtually the entire compositional range (0 le; x le; 2). For the purpose of evaluating their HDS activity, the particles are encapsulated in a mesoporous shell to inhibit sintering from the harsh reaction conditions (3 MPa, 548-673 K) used in industrial hydrotreating processes. The materials are evaluated with respect to surface and bulk composition (XPS, ICP), active site density (chemisorption) and metal ion site preferences (Td vs. square planar, assessed by Mössbauer). Preliminary data describing doping effects (x < 1) of Fe and Co in Ni₂P on dibenzothiophene HDS activity and product profiles will be presented and the results of these experiments discussed in the context of undoped samples of comparable size/polydispersity and compositionally equivalent TPR-prepared samples.

The unusual property of negative thermal expansion (NTE) is of fundamental interest and may be used to fabricate composites with zero or other controlled thermal expansion values. Many framework materials such as ZrW₂O₈ show NTE over a wide temperature range. NTE can also result from transitions between different electronic or magnetic states strongly coupled to the lattice, giving large negative expansions down to a previous record dilatometric value of -25 × 10^-6 / K for (Mn_0.96Fe_0.04)3(Zn_0.5Ge_0.5)N at 316-386 K. BiNiO₃ is an antiferromagnetic insulator with a unique charge distribution of Bi³⁺_0.5Bi⁵⁺_0.5Ni²⁺O₃ [1]. It shows a 2.6% volume reduction under pressure due to a Bi/Ni charge transfer accompanied by an insulator to metal transition [2, 3]. The charge transfer transition is shifted to ambient pressure through lanthanum substitution for Bi. Because the low-temperature and high-temperature phases coexist changing their fractions each other in a wide temperature range above room temperature, the weighted volume smoothly decreases on heating. The crystallographic linear expansion coefficient for Bi_0.95La_0.05NiO₃ is -137 × 10^-6 / K and a value of -82 × 10^-6 / K is observed between 320 and 380 K from a dilatometric measurement on a ceramic pellet [4]. The temperature range of NTE can easily be tuned by changing the amount of La substitution for Bi and by the substitution with other lanthanides. Substitution of Ni with other typical or transition metal ions which favor 3+ valence state also stabilizes the Bi³⁺(Ni,M)³⁺O₃ state and results in the appearance of NTE.
[1] S. Ishiwata et al., J. Mater. Chem. 12, 3733 (2002).
[2] M. Azuma et al., J. Am. Chem. Soc. 129, 14433 (2007).
[3] S. Ishiwata et al., Phys. Rev. B 72, 045104 (2005).
[4] M. Azuma et al., Nat. Commun. 2, 347 (2011)

The most straightforward procedure for fabricating inorganic semiconductor films is through solution processing because of the potential for low-cost and low-temperature deposition; however, the application of this method is frustrated by the low solubility of most inorganic semiconductors in known solvents. There are exceptions, such as a number of metal chalcogenides that are soluble in hydrazine, which is unfortunately highly toxic, carcinogenic, explosive and reactive. We have developed non-hazardous solvents capable of dissolving a range of technologically important V2VI3 semiconductors (i.e., As2S3, As2Se3, As2Te3, Sb2S3, Sb2Se3, Sb2Te3, Bi2S3, Bi2Se3, and Bi2Te3) at room temperature and ambient pressure. Solution deposition of phase-pure and highly crystalline metal chalcogenides was achieved upon drying and low-temperature annealing. This chemistry has also proven effective for the dissolution and redeposition of SnS, SnSe, Cu2Se, PbTe, Se, Te, As and P. These results point the way forward to a facile and a more benign semiconductor solution processing technology for electronic, photovoltaic, and thermoelectric applications.

Nanocrystalline materials are broadly explored as building blocks for LED&’s, solar cells, sensors, thermoelectric devices and printable electronics. At the same time, all nanomaterials are naturally metastable with respect to bulk crystals. This raises a very important fundamental problem of their morphological stability. In some cases, we need to preserve nanostructuring under operational conditions (e.g., in LED&’s and thermoelectric devices). In other cases, we use nanocrystalline particles as precursors for a material with large grains and want to sinter them as efficiently as possible (e.g., in thin-film solar cells). We carried out a systematic study of sintering and grain growth in materials composed of sub-10 nm semiconductor grains. The boundaries between individual semiconductor grains have been chemically engineered using inorganic surface ligands developed by our group. Our work also revealed several interesting and unanticipated trends. For example, III-V InAs nanocrystals are generally much more stable against sintering compared to II-VI CdSe nanocrystals despite the fact that bulk CdSe has 326^oC higher melting point than InAs (1268^oC vs. 942^oC). We found that sintering of nanocrystalline semiconductors is controlled by chemical stabilization of the grain boundaries that appears to be a general phenomenon for nano-granular materials. On the other hand, the grain growth can be dramatically accelerated when coupled to the phase transitions. These findings offer a versatile tool box for materials design and can impact all areas of applications of nanocrystal-based materials. By exploiting new chemistry for the interfaces in granular semiconductors, we were able to demonstrate record electron mobility over 170 cm²(Vs)^-1 in solution processed nanocrystalline semiconductor films and mold inorganic semiconductors into various shapes by using new type of functional inorganic “glue” for semiconductor grains.

Complex oxides of main group and transition metals have been a longstanding research focus due to the extensive range of properties that result from the electronic structure, and the library of metallic ions that can be intersubstituted in order to tune or transform the electronic behavior. For example, the combination of Mn and Ti cations in an oxide octahedral framework is appealing due to the substitutional similarity in terms of cationic radii and chemical precursor reactivity, while introducing distinctive and complimentary (potential magnetic, ferroelectric) properties of both ions. Moreover, for miniaturization and integration in electronics, homogeneous oxide nanocrystals, which can be processed easily into defect-free thin films, are appealing for the design of embedded functional devices by spin coating or printing. We have developed a novel general chemical processing route, called gel-collection, that enables the production of a variety of nanocrystalline oxide thin films and powders, and opens new synthetic pathways different from conventional solid state processing, with the subsequent ability to prepare new complex oxides. Using this method we present and characterize a novel class of complex oxides that demonstrate multiferroic behavior (ferroelectric, magnetic), conductivity, and a giant dielectric constant.

In the bulk form, Zn-Ga oxynitrides, solid solutions of GaN and ZnO, are capable of water splitting under visible irradiation. However, the methods used to synthesize these materials lead to polycrystalline particles with low quantum yields of water splitting. Furthermore, the bulk synthesis results in a limited range of compositions and a narrow range of band gap energies. We have developed a synthetic method for single-crystalline oxynitride nanoparticles with a broad range of compositions (ZnO fraction varying from 0.2 to 0.99) and band gaps that range from 2.7 to 2.2 eV. This was accomplished via chemical transformations of oxide nanocrystals. This presentation will focus on our current understanding of the synthesis that leads to nanocrystalline oxynitrides and on our studies of their properties that relate to solar fuel generation.

The advancement of nanotechnology is closely related to the precise and high-resolution analysis of the atomic structure and physiochemical properties of nanomaterials. Although gold is one of the most widely used elements in nanotechnology, element-specific studies on the structure and properties of gold in nanostructures are restricted to very few techniques. Synchrotron X-ray techniques such as X-ray absorption fine structure (XAFS) and X-ray photoemission spectroscopy (XPS) are desirable tools towards this end. In this talk, our results on X-ray spectroscopy studies of some recently emerged gold nanostructures will be presented. The nano-gold systems studied include high-index nanocrystals, composition-precise nanoclusters (~ 2nm or less), and gold-protein nanocomposites. It will be also shown that the joint use of X-ray spectroscopy with relevant techniques such as multi-element/multi-core detection, time-dependent measurement and ab initio calculation is particularly useful in these studies.

When constrained to ever smaller dimensions, many materials yield chemical and physical properties that are very different from their bulk analogues. Often these distinct properties are of considerable value in a wide range of technological applications. Indeed, the majority of heterogeneous catalysts that are used commercially, to refine raw fuel stocks, act as sensors, combat environmental pollution, or produce energy, rely on highly-dispersed nanoparticles (<5 nm diameter) of metals and/or metal oxides. Such nanoparticles are not passive, they adapt dynamically to their environment as they facilitate catalytic conversions. Thus the quantitative elucidation of their structure and reactive properties presents a significant challenge, requiring in situ probes that can be applied on suitable timescales. While the catalytic oxidation of CO to CO2 has been studied for almost a century, for both fundamental and applied reasons, the detailed picture of how this “simple” catalytic conversion is achieved continues to be an active area of research. This exemplifies the challenge in definitively resolving the relation between structure and function.
We apply pair distribution function (PDF) methods to interrogate dilute and dynamic catalytic systems in situ, during operation. This analysis allows the structure of the nanoparticles to be probed as they are working. Insight is gained into the dynamic structure and reactivity of the catalytically active phases.

Metal-dielectric heterostructures have received much interest in recent years because of properties due to the localized surface plasmon resonances at the metal/dielectric interfaces, such as sub-diffraction limit waveguiding and colossally-enhanced photoemission. Noble metal nanoparticle chains have been fabricated using several top-down methods such as lithography and templating, but the bottom-up approach of a peapodded nanowire is attractive because the nanoparticles form spontaneously within a protective ceramic nanowire shell during synthesis, and have the potential to be very well-defined in terms of size, spacing, shape, and interfacial orientation. Here we will present two complimentary transmission electron microscopy studies of these materials, observing their growth and evolution in situ, and mapping their plasmonic characteristics on the nanometer length scale - providing a direct link between structure, synthetic conditions, and functionality.

Uncontrolled oxidation negatively affects nanoparticle performance in applications that require pure metal surfaces. However, oxidation can be advantageous as it opens a way for engineering complex nanoparticle architectures. We used in-situ transmission electron microscopy to study room temperature nanoparticle oxidation for a special class of metals that oxidize by predominant anion diffusion (In, Sn, Pb, etc.) [1]. The formation of a native oxide transforms these particles into functional metal-oxide core-shell nanostructures.
Our understanding of metal oxidation has resulted primarily from studies on bulk materials or thin films. A priori, the oxidation of small particles should be governed by the same mechanisms, but exceptions arise at the nanometer scale. Our experiments on arrays of In nanoparticles show that the oxidation kinetics predicted by the conventional Mott-Cabrera theory requires significant corrections due to a non-uniform electric field, whose magnitude is increasingly amplified at the interface to the shrinking metal core. These results demonstrate for the first time the accelerated oxidation of nanoscale particles with high curvature [2].
Oxidation has especially interesting consequences for bimetallic alloy nanoparticles containing a non-noble, predomiant-anion oxidizing species and a noble metal. We show that such bimetallic systems avoid the usual phase separation and preferential oxidation of the non-noble species. Instead, exposure of Au-In nanoparticles to oxygen produces amorphous mixed oxide shells that contain highly dispersed, oxygen-coordinated Au atoms or clusters in the bulk and on the surface, and which remain stable in this configuration up to high temperatures [3]. The Au-rich mixed oxide is capable of adsorbing both CO and O₂ and converting them to CO₂. The transformation of Au-In alloys to a mixed Au-In oxide shows significant promise as a viable approach toward Au-based oxidation catalysts, which do not require any complex synthesis processes and resist deactivation up to at least 300°C.
[1] E. Sutter and P. Sutter, Appl. Phys. Lett. 100, 231602 (2012).
[2] E. Sutter and P. Sutter, J. Phys. Chem. C 116, 20574 (2012).
[3] E. Sutter, X. Tong, K. Jungjohann, and P. Sutter, Proc. Nat. Acad. Sci. USA (doi: 10.1073/pnas.1305388110, 2013).

We report a citrate-free synthesis of Ag nanoplates with an edge length of 50 nm that involved the reduction of AgNO3 by poly(vinyl pyrrolidone) (PVP) in ethanol at 80 oC under a solvothermal condition. Within a period of 4 hours, >99% of the initially added AgNO3 could be converted into Ag nanoplates with excellent stability. To understand this remarkably simple and efficient process, we systematically investigated the roles played by various reaction parameters, which include the type of precursor, the reducing powers of PVP and ethanol, the molar ratio of PVP to AgNO3, the solvent, the involvement of O2, and the effects of pressure and temperature. Our results suggest a plausible mechanism that involves i) fast reduction of AgNO3 to generate Ag multiple twinned particles (MTPs) via a thermodynamically controlled process, ii) kinetically controlled formation of plate-like seeds and their further growth into small nanoplates in the presence of Ag+ ions at a low concentration, and iii) complete transfer of Ag atoms from the MPTs to nanoplates via O2-mediated Ostwald ripening. We demonstrated that the molar ratio of PVP to AgNO3 in ethanol plays an essential role in controlling the reduction rate for the formation of MTPs and plate-like seeds under the solvothermal condition, the transformation kinetics, and the final morphology taken by the Ag nanoplates.

Structural characterization is a central driver of new materials innovation, providing an important understanding of new properties, which in turn accelerates the next breakthrough discovery. Powder diffraction is one of the key tools for structural characterization, used early and often in many fields of solid-state chemistry research, not only as guide of synthetic exploration, but also to gain detailed insights of structure - properties connections under ambient and a flexible range of in-situ operating conditions.
This presentation will highlight characterization possibilities for solid-state chemists made possible by the high-resolution synchrotron powder diffraction beamline 11-BM at the Advanced Photon Source (APS). This start-of-the-art probe enables diffraction experiments under ambient and in-situ conditions with exceptional resolution and fidelity. A unique remote mail-in mode facilitates convenient access to world-class data acquisition for both expert and non-traditional synchrotron users.
Particular focus will be given to recent advances illustrating multi-probe characterization methods combining synchrotron powder diffraction and other cutting-edge techniques (e.g. neutron scattering, NMR), and examples will be presented to spotlight the evolving suite of APS in-situ sample environments developed that provide the structural details required for an understanding of the novel magnetic, transport, optical, and electrochemical properties in inorganic materials of interest to today's solid-state community

Early single-molecule spectroscopic investigations of semiconductor nanocrystals (NCs) revealed unforeseen spectral dynamics that report on interactions between the core states of NCs and their local electronic environment. However, these investigations could not fully resolve an important regime of fast spectral dynamics because of the fundamental limitations of conventional techniques. We have combined single-molecule spectroscopy with photon-correlation Fourier spectroscopy to measure spectral dynamics in NCs over the full range of pertinent timescales from microseconds to hundreds of seconds. This has allowed us to directly observe the discrete nature of rapid spectral diffusion in NCs and given us a new avenue for studying the local environment of NCs.

Two New Bismuth-Based chalcohalides have been synthesized by the solid-state reactions at high temperatures. Compound 1 and 2 display the band gaps of 0.67 eV and 0.75 eV, respectively. The use of 455 nm laser incident on the pressed pellets of the materials induce the high concentrations of conductive carriers that can be applied to shield terahertz waves. For 1 and 2, the shielding of terahertz wave at 0.15 THz with 325 mW can reach about 70%, which extent is superior to the nanorods of CdSe with 16% modulation at 0.34 THz. The substitutions of elements in the compositions of 1 and 2 are performed to increase the stability of samples sustaining in the reversible process between the excited and ground states.

Low-dimensional oxides with disconnected magnetic units are of increasing interest due the peculiar properties and the versatile interplay between individual magnetic moments into an external magnetic field. Our group is interested in the elaboration of such modular new compounds and their characterization by combining experimental (XRD, ND, magnetic) measurements and theoretical calculations. Our main strategy focuses on magnetic sub-units formed of anisotropic magnetic ions (Fe2+, Co2+) isolated by big spacers (Ba2+, XO43-, X2O74-) Here, we present several new compounds in which magnetic properties are mediated by complex structural features. For instance hellip;
- BaFe2(PO4)2 was recently prepared in hydrothermal conditions and identified as the first 2D-Ising ferromagnetic (FM) oxide, Tc =65.5K. It contains isolated honeycomb layers made up of edge-sharing FeO6 octahedra with high-spin Fe2+ ions (S=2) [1a]. On cooling, BaFe2(PO4)2 undergoes a rare re-entrant structural transition R-3(RT)P-1(140 K) → R-3(Tc) due to Jahn-Teller distortion in competition with FM magnetostrictive effects [1b]. Furthermore, around 700K, it undergoes a topotactic and reversible Fe ex-solution into several ordered superstructures containing new Fe-depleted triangular lattices with mixed valence Fe2+/Fe3+. The relationships between the crystal structures and the versatile magnetic properties will be discussed on the basis of accurate crystal structures refined by single-crystal XRD.
- Another striking example concerns the BaCo(X2O7) series (X=P, As). We will show how an incommensurate structural modulation assorted with strong atomic displacements is responsible for magnetization steps under an external field. Briefly, the displacement waves transform Co2+ 1D-chains (average structure, spacegroup P-1) into 2D-layers (4D-model ; superspacegroup P-1(αβγ)0 ) with a distribution of strongly frustrated Co2+ triangles [2]. The exchanges calculated by DFT (in agreement with our PND results), show that they are mainly responsible for the stepped magnetization along AFM→ FERRI→ FM transitions.
These new compounds will be discussed in terms of their possible application for storage devices.
[1] a) H. Kabbour et al., Angewandte Chemie, Int. Edition, (2012) , 51, 11745. b) R. David et al., J. Am. Chem. Soc. (2013), in press. [2] R. David et al., J. Phys. Chem. C. (2013), submitted.

Protonic ceramic fuel cells (PCFCs) based on proton conducting ceramics, which have great potential to be operated at lower temperatures (300-600oC) than traditional solid oxide fuel cells (SOFCs) based on oxygen ion conducting ceramics, have received significant scientific and technological attention in recent years. Among PCFCs, the recently reported single cell of 35wt%BaCe0.7Zr0.1Y0.1Yb0.1O3minus;δ+65wt%Ni|BaCe0.7Zr0.1Y0.1Yb0.1O3minus;δ|BZCY-LSCF has shown particularly promising performance at test temperatures around 750oC. However, the performance at lower temperatures (300-600oC) is still inadequate for practical applications, due primarily to the lack of proper cathode materials that are compatible with protonic ceramic electrolytes. Accordingly, the development of new intermediate-temperature cathode materials with earth abundant elements, enhanced electrocatalytic properties, structural/chemical stability, and compatibility with protonic ceramic electrolytes has become a major emphasis of research in the fuel cell community. In the search for new PCFCs cathode materials, we have drawn recent inspiration from oxygen permeation membrane reactor studies employing a BaCo0.4Fe0.4Zr0.2O3-δ (BCFZ) perovskite MIEC membrane, which was shown to operate successfully for more than 2200 h under a very harsh gradient of air/syngas. Thus, based on its stability and good performance in membrane reactor environments we hypothesized that BCFZ could be an intriguing cathode material for PCFCs as well. Despite the promising properties of BCFZ, however, there have been no literature reports on its electrochemical performance or compatibility for PCFCs applications. In this work, we therefore present for the first time the highly promising results on the application of the perovskite-type oxide BCFZ as a cathode for IT-PCFCs using the state of the art proton conductor BCZYYb as an electrolyte and BCZYYb-Ni cermet as an anode. BCFZ exhibits good electrochemical performance and high stability with a proton-conducting BCZYYb electrolyte. Our study of the ORR process on the BCFZ cathode indicates that the polarization resistance may be due to both proton diffusion and oxygen ion diffusion processes. The performance of a pellet-type BCZF/BCZYYb/BCZYYb-65%NiO fuel cell further confirms the potential of the BCFZ cathode material with an open-circuit potential of 0.97 V and a power density of 225 mW/cm2 at 600 oC, which is ~20 times greater than a single cell constructed from an LSCF cathode with the same electrolyte and anode under the same operation conditions.

The localized surface plasmon resonance frequencies of copper sulfide nanocrystals are tunable by controlling nanocrystal shape and carrier density. Access to carrier densities in the range of 10^20 to 10^22 cm-3 is achieved by utilizing different chemical syntheses (solventless and solvothermal processes) to generate nanocrystals possess various stable solid-state copper sulfide phases. These phases include CuS, Cu7.2S4 and Cu1.96S, where carrier density is increased as copper content is decreased. Anisotropic nanocrystal growth is furthered tuned by the presence of additives that control nanocrystal ripening. For example, we demonstrate that the shape of copper monosulfide (CuS) nanocrystals can tuned from disks to triangles upon the addition of various halide ions during solvothermal synthesis. Shape and carrier density tuning enable plasmon resonance engineering across the near- to mid-infrared wavelength ranges for these semiconductor nanostructures.

The synthesis of layered perovskites is often achieved by the ceramic method at high temperatures. However, some compounds cannot be readily obtained by direct reaction of binary metal oxides. A multi-step approach was investigated based on the solid-state reaction of known layered perovskites with simple ABO3 perovskites. The synthesis of new layered compounds with the general formula RbLaAn-2Nb2Bn-2O3n+1 with n = 3, 4, for example, were sought through the combination of RbLaNb2O7 and the simple perovskites (A = Na, Ca; B = Ti, Mn, Nb). The resulting compounds were then manipulated topochemically at low temperatures (< 500 °C) using A&’NO3 (A&’ = alkali metal) or first row transition metals halides. Details on the synthesis and characterization of this series of compounds will be presented and their potential utility in further topochemical manipulations discussed.

The continued shrinking of microelectronic devices has led to the need for lower dielectric constant (low-k) materials in back-end interconnect structures to reduce resistive-capacitive delay in signal propagation. In order to reach lower dielectric constants traditional materials are used as a starting point, but are fabricated to promote the formation of pores. Higher levels of porosity reduce the dielectric constant, but also result in a loss of mechanical strength.
We have modeled low-k organosilicate glasses using molecular dynamics techniques in order to understand the relationship between the material&’s structure, porosity, dielectric constant, and mechanical strength. In this paper, we use the REAX-FF force field to model the material&’s atomic interactions. This force field is unusual because it allows for the breaking and forming of bonds during the simulation. This capability allows us to follow the evolution of the bonding environment of the material&’s structure as we change the thermal environment of the system. Ultra-rapid thermal annealing is of interest since it offers the potential to strengthen the material with minimal increase in dielectric constant.
We begin by establishing a starting REAX-FF model of these SiCOH-type materials with the appropriate composition and bulk properties to match an experimental film. We then simulate thermal annealing of this material, after establishing a simulation-derived glass transition temperature (Tg) (~1200°C) to use as a point of reference. By comparing the structure at Tg with the starting structure, as well as the evolution of the structure at all temperatures along the way, we are able to link temperature to structural and property changes. We show how the structure evolves with increased temperature to eventually result in a dense Si-O based structure, surrounded by loose, gaseous organic material. This transition is confirmed by complimentary experimental results. We also suggest processing paths to lead to a balance between mechanical strength and dielectric constant and draw comparisons to experimental laser spike annealing results.

Strongly correlated materials are often characterized by spatially localized charge or spin ordering motifs that give rise to intriguing electronic instabilities ranging from charge density waves to metal-insulator transitions and superconductivity. Ternary vanadium oxide bronzes (MxV2O5) provide a unique class of compounds for studying the effects of correlated electrons on low-dimensional systems. The layered framework of V2O5 permits cations (M = K+, Cu+, Ag+, Pb2+, etc.) to enter the layers that then rearrange to adopt the 1D tunnel framework of the β/βprime;-phase or the double layered δ-phase. The intercalated cation is completely ionized, thereby partially reducing the V2O5 framework to create localized V4+ sites and producing charge ordered networks that yield 1D electron transport. Carrier transport in ternary vanadium oxide bronzes is extremely sensitive to cation stoichiometry and charge ordering; difficulties in precise control over the cation stoichiometry have thus far impeded extensive exploration of the electronic phenomena found in vanadium oxide bronzes. We have been able to overcome this problem by utilizing a hydrothermal approach to the synthesis of single-crystalline nanowires. Self-purification during growth as a result of the short diffusion path length of the nanowires permits defects to migrate to the surface, yielding almost perfectly crystalline solids with precise ordering of the cations at interstitial sites.
We have examined the synthesis, characterization, and electronic transport properties of strongly correlated ternary vanadium oxide bronzes. Specifically, intercalation of Ag+ in the V2O5 framework stabilizes both δ- and β-phases depending on the Ag+ concentration. For Ca2+ bronzes dehydration of the δ-phase induces transformation to the β-phase for nanowires; the β-CaxV2O5 nanowires can be reversibly transformed to δ-CaxV2O5 by hydrothermally induced hydration. The voltage and temperature induced metal-insulator transition of vanadium oxide bronze nanowires and pellet samples permits a unique glimpse of the electronic properties without obscuration from defects or cation vacancies. First-principles DFT calculations suggest anisotropic lowest energy conduction band states in δ-AgxV2O5, while the complex nature of the 1D tunnel β-phase induces an intricate bond network for the lowest energy conduction band states. Polarized near-edge X-ray absorption fine structure (NEXAFS) spectroscopy allows for experimental confirmation of the lowest energy conduction band states for δ-AgxV2O5, while the compacted bond network of β-AgxV2O5 makes experimental confirmation of the DFT calculations difficult. β-MxV2O5 (M = Ag, Pb) are also characterized by a mid-gap state between the valence and conduction bands. We gratefully acknowledge support of this work by the National Science Foundation (DMR 0857169) and the Research Corporation for Science Advancement through a Cotrell Scholar award.

FeMnAs crystallizes in two phases under different synthetic conditions: (i) the tetragonal Cu2Sb-type structure at normal conditions; or (ii) the hexagonal Fe2P-type structure at high pressure and temperature. In both phases, Fe atoms occupy half of the tetrahedron holes formed by As atoms, while Mn atom is square pyramidally coordinated by As atoms. VASP total energy calculations reveal that hexagonal Fe2P-type FeMnAs is lower in energy than the tetragonal Cu2Sb-type one by only 0.86 meV (~10 K). Hence the two phases of FeMnAs could be compatible at even low temperature. To better understand the stability of two phases under different synthetic conditions, two energy terms were examined using a TB-LMTO program, the bonding energy term and the band energy term (energy of valence electrons). Our results show that the tetragonal Cu2Sb-type structure is favored when the band energy is low, while the hexagonal Fe2P-type structure is preferred when the absolute bonding energy value is large. In addition, the tetragonal phase is antiferromagnetic (TN = 470 K) with a doubled crystallographic c-axis, whereas the hexagonal phase is ferromagnetic with TC near 190 K. Effective exchange parameters obtained from SPRKKR calculations indicate that both direct and indirect exchange couplings play essential roles in understanding the magnetic orderings observed in both tetragonal and hexagonal phases.

Vanadium(IV) oxide has been studied intensively due to its massive reversible first-order metal-to-insulator transition wherein it transforms between a low temperature, monoclinic insulating phase and a high-temperature, metallic rutile phase. Accompanying this transition are changes in electrical conductivity, and optical transparency that can range across several orders of magnitude. These optical properties are of particular interest for use as thermochromic coatings in energy efficient fenestration since the low-temperature insulating phase is infrared transparent, whereas the metallic phase is infrared reflective. Through scaling to finite size and substituting vanadium with cations such as W⁶⁺ or Mo⁵⁺ it is possible to reduce the phase transition temperature from the bulk temperature of 340K to as low as 303K. This places the transition within an acceptable range for applications such as “smart” windows. Apart from temperature tunability as a function of size and dopant concentration, nanostructured coatings present a distinct advantage over more conventional coatings such as continuous thin films due to the ease with which nanostructures are able to accommodate the strain associated with the change in volume between the two structural phases. This results in reduced deterioration, improved cycling, and enhanced lifetime of such coatings. This work was supported by the National Science Foundation under IIP 1311837. We also gratefully acknowledge support from the SUNY Technology Accelerator Fund.

In this study, our aim is to investigate the effect of annealing time in flowing oxygen on structural and electric properties of the rutheno-cuprate RuSr2GdCu2O8±z (Ru-1212). By means of solid-state reaction at ambient pressure, Ru-1212 was prepared at temperature between 960 °C to 1040 °C in air. Powder x-ray diffraction indicates the formation of a pure phase. Oxygen treatment was carried out at 1060 °C for 24, 48, 96, 144 and 240 hours. After each treatment, the structure of the samples was investigated by Rietveld refinement. The results indicate that the parameters cell a and c as well as Cu-O(1) increase with the time of flowing oxygen. The electrical resistance measurements show that the samples annealed in flow oxygen for 24, 48 and 96 hours present semiconductor behavior, whereas the samples with oxygen treatment for 144 and 240 hours show a superconductor behavior with TC = 24 K and 30 K respectively. These results indicate that the structural and electric properties of the Ru-1212 compound are strongly related.

Silicides containing transition metals such as manganese and iron have attracted much attention because they are composed of non-toxic and abundant elements with unique electrical properties. In particular, the silicide-based fine particles have been promising for the raw materials of the nanostructured thermoelectric bulk materials, battery electrodes with enhanced performance and so on. In this study, we demonstrate that composite particles of Mn silicides fine particles and Ca-deintercalated calcium silicide or silicon are synthesized by a novel synthetic route, Solid-State Exfoliation Reaction (SSER). In this reaction, layered CaSi2 (starting material) reacts with MnCl2 through SSER under heat treatment, which leads to the deintercalation of Ca from CaSi2 by chloride species and the formation of Mn silicides by CaCl2 formation as the driving force. Therefore, the obtained species of composite particles vary depending on the molar ratio of MnCl2 to CaSi2 (denoted by x) in SSER. Under the condition of x ge; 1, MnSi1.73 and Si particles are assumed to form (CaSi2 + MnCl2 → MnSi1.73 + 0.27Si + CaCl2). On the other hand, MnSi1.73 and Ca-deintercalated CaySi2 (y < 1) are expected to form due to the insufficient amount of MnCl2 under the condition of x < 1.
Under the condition of x = 2, relatively large-sized MnSi1.73 particles (> 300 nm) with Si particles formed after heating at 600 °C. In contrast, composites of MnSi1.73 and Ca-deintercalated CaySi2 were obtained under the condition of x = 0.5 after the same heat treatment, and the MnSi1.73 primary particles have the size with less than 200 nm in TEM images, which is smaller than those prepared by conventional methods. Thus, the size of MnSi1.73 particles and the selective formation of Ca-deintercalated CaySi2 or Si were controlled by the ratio of MnCl2 to CaSi2 in SSER. In the application of the composite particles to photoelectodes deposited on FTO substrates, the powder prepared under the condition of x = 0.5 was found to show photocurrent under visible light irradiation in 0.2 M K2SO4 solution, whereas Si powder or the composite particles prepared under the condition of x = 2 showed no response under visible light irradiation. This result suggests that the presence of Ca-deintercalated CaySi2 affect on the visible-light response.

Mn-rich LiFe1-yMnyPO4 is a promising cathode material for Li-ion battery due to the higher redox potential of Mn2+/3+ as compared to Fe2+/3+ in the olivine structure which has to maintain stability during hundreds of charge-discharge cycles and various application conditions. In our previous work, we reported the good structural stability of o-LixFe1-yMnyPO4 (0le;yle;0.9), and elucidated the critical role of moisture in the low-temperature decomposition of delithiated Mn-rich phases. However, pure crystalline MnPO4 is difficult to obtain and has been considered unstable. Here we report a comprehensive study of the structural stability of MnPO4. LiMnPO4 with different particle sizes and carbon contents were synthesized by a solid state method. Pure MnPO4 has been obtained successfully by chemical delithiation of LiMnPO4, except for carbon-free samples, as confirmed by ICP and X-ray diffraction analysis. A variety of techniques including high-temperature in-situ x-ray diffraction (XRD), TGA-MS, XPS, and XAS were applied to investigate the structure and thermal stability of MnPO4. The results indicate that the structural stability of MnPO4 depends on many parameters. Upon heating, an intermediate sarcopside phase Mn3(PO4)2 forms at ~400 °C, and the final product is Mn2P2O7. Small amounts of carbon helps to stabilize the structure, while large amount of carbon decreases the thermal stability of MnPO4. The role of particle size, carbon content, moisture level and heating atmosphere will be discussed. This work was supported by the Northeastern Center for Chemical Energy Storage, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DESC001294.

Elemental boron (B), such as β-rhombohedral B (β-B), has a framework crystal structure built up from B12 icosahedral clusters. β-B has comparatively large interstitial sites; therefore, there have been some attempts to dope other elements into β-B. Vanadium (V) occupies the A1 site of β-B and electrical conductivity changes from semiconducting to metallic only by 1 at. % doping. This is considered to be metallic-covalent bonding conversion [1,2]. On the other hands, Magnesium (Mg) and lithium (Li) mainly occupies the D and E sites and electrical conductivity stays semiconducting even 8 at % (Mg) or 17 at % (Li) doping. For Li or Mg mono-doping, Li or Mg donates electrons to β-B and as a results, β-B self-compensates the electron doping with disappearance of the interstitial B atoms and generation of the vacancies [3,4]. The self-compensation is originated from a complex structure of β-B and is unique in boron crystal among elemental ones. In this research, we doped Li or Mg into V doped β-B and discussed the change in the structure, electrical conductivity and stability.
The V occupancy gradually decreased according to the increase of Li or Mg concentration. When the number of doped electron was 10/cell, V completely removed. Disappearance of V occurred in order to compensate the electron doping from Li or Mg. The electrical conductivity of V and Li or Mg co-doped β-B was not metallic but semiconducting. From the total energy calculation, V and Li co-doped β-B was less stable than Li doped β-B. Thus, disappearance of V by electron doping can be interpreted as “Extended self-compensation” because V reduction has an effect of the compensation of electron doping and the stabilization. Also, this is considered to be metallic-ionic bonding conversion.
[1] K. Kimura et al., J.Solid State Chem. 133, 302 (1997)., [2] M. Yamaguchi et al., J.Phys. :Conf. Ser. 176, 012027 (2009)., [3] H. Hyodo et al., Phys. Rev. B 77, 024515 (2008)., [4] H. Hyodo et al., Solid State Science 14, 1578 (2012).

Nanocrystalline Hf₃N₄ is produced by solution phase reaction of Hf(NEtMe)₄ with ammonia followed by low temperature pyrolysis in ammonia. The phase behaviours of such systems are important because early transition metal nitrides with the metal in maximum oxidation state are potential visible light photocatalysts. A combination of synchrotron powder X-ray diffraction and pair distribution function studies have been used to show this phase to have a tetragonally distorted fluorite structure with 1/3 vacancies on the anion sites. Laser heating nanocrystalline Hf₃N₄ at 12 GPa and 1500 K in a diamond anvil cell results in its crystallization with the same structure type. This is an interesting example of pre-structuring of the phase during preparation of the precursor compound. Such a metastable pathway could provide a route to other new polymorphs of metal nitrides and to nitrogen-rich phases where they do not currently exist. Importantly it leads to bulk formation of the material rather than surface conversion as can occur in elemental combination reactions. Laser heating at 2000 K at a higher pressure of 19 GPa results in a further new polymorph of Hf₃N₄ that adopts an anion deficient cottunite-type (orthorhombic) structure. Orthorhombic Hf₃N₄ phase is recoverable to ambient pressure and the tetragonal phase is at least partially recoverable. ¹
1. A. Salamat, A. L. Hector, B. M. Gray, S. A. J. Kimber, P. Bouvier and P. F. McMillan, J. Amer. Chem. Soc., 2013, in press (DOI:10.1021/ja403368b).

By wet sol-gel method using polyacrylamide gel formation on two different synthesis routes with anionic polyacrylamide in direct method and polyacrylamide by in situ method were synthesized High Temperature Superconductors (HTS) BSCCO doped with La, Eu and Nd, with a subsequent heat treatment of the product in a muffle furnace at temperatures of 180C, 600C and 800C respectively, the product was ground to obtain powder dark color, and it was determined weight loss in each of the heat treatments.
The material was pressed into pellets of 13 mm thickness. The critical temperature was characterized by magnetometer and the material structure by X-ray diffraction and SEM. These phases of the high temperature superconducting materials showed a critical temperature (Tc) of 106K, where the product of synthesis was in polycrystalline form. In this synthesis that combines the wet method and the traditional ceramic method reduces the time transformation to obtain the high temperature superconductors. In order to improve the reaction yield and reduce the synthesis time, the experiments were carried out several times.

The physical properties of nanoparticles are determined by the balance between size effects and the intrinsic properties of bulk materials. Preserving the crystalline structure of reference is therefore a challenge that adds up to the already delicate problematic of size and dispersion control. Considering aqueous coprecipitation of oxide nanoparticles whose diameter is typically higher than 20 nm, the obtained particles often present a hierarchical structure. Among them, YVO4:Eu luminescent particle presented here are made of ~4 nm primary grains assembled into ovoidal-shaped nanoparticles (~30 nm).[1] This porous nanostructure is interesting for several applications such as in situ H2O2-detection due to their high specific surface area.[2] However, for other application such as nanophosphors for lighting devices, perfect crystallinity is necessary to maintain bulk efficiency. Understanding each step of YVO4:Eu nanoparticle formation should help us to drive the particle nanostructure toward the desired application.
Time-resolved X-Ray scattering experiments (SAXS/WAXS) coupled with time-resolved photoluminescence at synchrotron SOLEIL were used to study YVO4:Eu luminescent nanoparticle formation. We show that this powerful tool allowed us to follow the outer structure (shape evolution) and the inner one (crystallization) with time. Yttrium, Europium and orthovanadate precursors are found to precipitate instantly in a poorly luminescent but structured amorphous phase. This first step appears to be crucial as it already constraints the final particle nanostructure. That precipitate is indeed loosely structured but already presents the two characteristic sizes observed in the final particles. Starting from the amorphous phase, crystallization of primary grains occurs through a direct conversion and no further growth is detected. This behavior could be referred to as a “pop-corn” nucleation. One minute later, aggregation of the primary grains occurs and nanoparticles are detected. They appear to grow during the grain production but this stops after reaching a predetermined size.
From these observations, we may infer that the two sizes in the hierarchical structure of the final particles were determined during the amorphous phase precipitation. For the first time, we thus witnessed a topologically constrained amorphous-to-crystal conversion that opens to new strategies concerning the microstructure control of many other systems presenting an amorphous-to-crystal transition during their formation.
References
1. A. Huignard et al. Chem. Mater. 12, 1090 (2000)
2. D. Casanova et al. Nature Nanotechnology 4, 581 (2009)

Recently, the very promising applications of gold nanorods for medical applications or in plasmonics reinforce the research for new direct synthetic scheme with high yields and no pollution by other shapes.[1] Anisotropic nanoparticles are generally obtained after a seeded growth method based on isotropic seeds.[2] The procedure is well described in the literature but the control and prediction of size and polydispersity in a large scale remains a difficult task. The main reason is certainly the difficulty in the control of concentration, size and crystallinity of the initial seeds (2-5 nm). Recent studies performed in our lab have evidenced the importance of the seed crystal structure as a guide to obtain different anisotropic final shapes. If HRTEM is a powerful technique to identify the nature of the small crystals and their defects, a full statistical analysis is out of range.
In the field of diffraction, total scattering experiments coupled with real-space analysis appears as a good alternative to probe directly in solution the internal structure of small nanoparticles with good statistics.[3],[4]
Here we report scattering measurements on gold nanoparticles in solution at different steps of their anisotropic growth. The DISCUS package[5] and Reverse Monte-Carlo modeling was used to build and refine the particle structure and morphology. We could follow the internal defects and shape evolution during the growth from the very beginning to the nanorods. The comparison of the obtained structure with a regular FCC organization evidenced strong surface disorder in those small objects and strong correlated atomic displacements. By performing the same study on dried samples, we could also characterize the atomic reorganization during the drying.

REFERENCES
[1] S. E. Lohse et al. Chem. Mater. 25, 1250minus;1261 (2013)
[2] N. R. Jana et al. J. Phys. Chem. B, 105, 4065-4067 (2001)
[3] V. Petkov et al, Physical Review B 72, 195402 (2005)
[4] K. Page et al. J. Appl. Cryst. 44, 327 -336 (2011)
[5] R. B. Neder, T. Proffen, Diffuse Scattering and Defect Structure Simulation, Oxford (2008)

Layered materials containing coordinatively unsaturated binding sites such as 5-coordinated Al species show great promise in many applications. Here we report a new one-pot solvothermal synthetic strategy for synthesizing such materials based on a modified yet rigorous transesterification reaction mechanism. The novel layered sodium aluminoglycolate complex [Na3Al4(CH3O)3(OCH2CH2O)6] prepared by this method is characterized by using single crystal and powder X-ray diffractions (SCXRD and PXRD), 27Al MAS NMR, 13C MAS NMR, FT-IR, and TGA. SCXRD and 27Al NMR indicate that a unique tetranuclear Al complex was formed containing three penta-coordinate Al3+ ions, each bound to two bidentate ethylene glycolate ligands and one monodentate methanolate ligand, as confirmed by 13C NMR analysis. The remaining fourth Al3+ ion is octahedrally coordinated to one oxygen atom from each ethylene glycolate ligand, effectively stitching the three penta-coordinate Al moieties together into a novel, oligomerized tetranuclear complex. The compound crystallized in space group P21/c with a = 11.2481(12) Å, b = 13.1877(14) Å, c = 18.235(2) Å, α,γ = 90°, β = 105.738(2)°, and Z = 4 measured at -173.0 °C. The complex is arranged in well-ordered layers parallel to the [110] direction of its monoclinic crystal structure with the intra- and inter-layer bindings involving extensive ionic bonds from the three counterbalancing Na+ cations instead of the more typical hydrogen bonding interactions, as corroborated by FT-IR analysis. The unusually large shift of the penta-coordinate Al in the 27Al NMR spectrum redefines the acceptable NMR shift range for the Al3+ nuclei. The versatile synthetic methodology proposed in this study is expected to open up a new avenue for elegantly designing new porous metallorganic materials.

Recently, one of the frontier fields in material research has been morphology-controlled synthesis of nanometarials, since novel optical and electronic properties is directly affected by special particle sizes and shapes1. Germanium material is a IVA group semiconductor, with a high refractive index and high dielectric constant, which is widely applied in the field of the photoelectric sensors, gas sensors, optical communication infrared sensors and so on. Germanium particles with a controlled morphology have a special photoluminescence, electroluminescence, surface enhanced Raman and also other special effects2.
Due to the strong covalent bond, germanium nanoparticles of controlled morphology is difficult to obtain, there are only few relative literatures. Wang, et al reported a Synthesis mehod of germanium nanocubes by a Inverse Micelle Solvothermal Technique3. Yang et al first reported solid-state synthesis of silicon nanocubes with edge lengths of 8-15 nm4.
In this paper, we present a method of preparing Ge nanocubes and controlled morphology by UV-assisted eletrodeposition from an ionic liquid (EmimTf2N). Ionic liquids (ILs) are solely composed of ions and have advantageous properties like negligible vapor pressure, high thermal stability and wide electrochemical windows5. As a room-temperature method, ionic liquid (IL) electrodepositon represents for the new energy-saving. It also solves the problem that semiconductor materials could not be obtained from aqueous or other organic solutions in that hydrolysis will happen before the reduction of the concerned ions6, 7. Recently, Endres group prepared germanium film assisted by UV method was electrodeposited by in ionic liquid Py1,4Tf2N with green fluorescence8. Here, we present a nanocubes and other aspherical germanium electrodeposited in ionic liquid EmimTf2N assisted by low-power UV light within 15 min. The influence of UV on the reduction potential and the open circuit voltage are studied by electrochemical methods. And the morphology transformation is observed by SEM. The germanium nanocube is prepared by 365nm UV irradiation for 10min electrodeposition in the EmimTf2N, which is aggregated by smaller germanium particles with the edge length of 100-200nm. The special germanium nanocubes may have potential applicaition value in many fields.
1. P. Bettotti, et al , J Phys-Condens Mat, 2002, 14, 8253-8281.
2. C. H. Kim, et al, J. Phys. Chem. C, 2012, 116, 26190-26196.
3. W. Z. Wang, et al, Langmuir, 2005, 21, 751-754.
4. Z. Y. Yang, et al, J. Am. Chem. Soc., 2012, 134, 13958-13961.
5. S. Z. El Abedin et al, Chemphyschem, 2006, 7, 58-61.
6. S. Z. El Abedin, et al, Electrochem. Commun., 2004, 6, 510-514.
7. F. Endres et al, Chem. Commun., 2002, 892-893.
8. A. Lahiri, et al, J. Phys. Chem. C, 2012, 116, 17739-17745.

Improving temperature stability of light alloys based on aluminium is a challenge which has raised a significant interest for the study of the influence of small zirconium additions in this class of materials. Zr actually belongs to the category of transition metals which form an Al3X compound chemically ordered according to the L12 structure, which is expected to provoke a significant hardening by precipitation at high temperature. In this structure, which is based on a face centred cubic lattice, Zr atoms occupy the summits of the cube whereas Al atoms positions are at the centre of the faces. One of the main features of Al3Zr precipitates is their high temperature stability, which is related to the very low diffusivity of Zr in Al. According to the literature available on the formation of Al3Zr precipitates in aluminium, the precipitation of Al3Zr is known to lead to the formation of coherent interfaces with the Al-matrix and precipitates commonly exhibit a L12 metastable structure which is replaced by the stable DO23 structure for higher ageing temperature and/or long ageing times. Very few information is available on the actual effect of Al3Zr precipitates on dislocation motion in the Al crystal although a transition from precipitates shear to Orowan bypassing is expected. In addition, the L12 chemical order of precipitates constitutes a favourable case for the investigation of precipitates shear, insofar as slip systems activated during cold deformation of aluminium is ½ <1-10> {111}are expected to induce antiphase boundaries (APBs) in L12 structures.
In the present work, the evolution of the structure of Al3Zr precipitates structure during cold deformation of an Al-based alloy has been studied. Special attention has been paid to the transition from precipitates shear to the Orowan bypass mechanism. For this purpose, the structure of precipitates was investigated at the atomic scale by high angle annular dark field scanning transmission electron microscopy (HAADF-STEM). The unambiguous observation of a complex combination of lattice translations, revealed by the position of Zr-rich columns in precipitates, is used as the signature of precipitate shear during cold deformation. Experimental findings are here confronted to a classical statistical model of precipitation hardening, therefore enabling the determination of a critical precipitate radius for the shear-bypassing transition in the system investigated. In addition, the atomic mechanism controlling the L12 to D023 transition is described in detail.

High-temperature piezoelectric crystals with crystal structures similar to langasite (La3Ga5SiO14) have been demonstrated to show piezoelectric properties even above 1000 °C. Thus, these crystals are applicable in high-temperature bulk-acoustic-wave (BAW) and surface acoustic wave (SAW) devices. Applications of such devices include wireless temperature, pressure and gravimetric mass sensing. However, a potential drawback of many members of the langasite family is a partially disordered crystal structure, which involves some types of the lattice sites being occupied randomly by one of two atomic species. Such statistical occupancy distributions may lead to increased loss and decreased frequency stability at elevated temperatures, which, in turn, will introduce uncertainties in frequency determination of resonant devices.
In contrast, a number of less-studied crystals in the langasite family, including commercially available CTGS (Ca3TaGa3Si2O14), have fully ordered crystal structures and, therefore, potentially superior electromechanical properties at elevated temperatures. In this study, the acoustic characteristics and electrical properties of CTGS disk resonators are measured in the temperature range from room temperature to 970 °C. The resonators were fabricated with an orientation of (YXl) -30° and a fundamental frequency of 5 MHz. At moderate temperatures, a sample support is used which impacts the overall loss of blank resonators in a minor way. A room-temperature Qf value of ~ 3.5x10^12 Hz is found at the fifth-overtone frequency of 25 MHz. This value of Qf is less than the highest values previously reported for langasite at room temperature. For measurements above ~ 700 °C, thin platinum electrodes are used, and this enables operation up to at least 970 °C. As expected, the Q factor of the crystals is found to decrease, overall, with increasing temperature, but also shows evidence for frequency-dependent dips versus temperature arising from anelastic relaxations. At the highest measured temperatures, the Q factor at 5 MHz is 2200, which is substantially greater than that of previously measured langasite crystals at similar temperatures. The temperature dependence of the frequencies is found to be less than 37 ppm/K over the measured range. The parameters of the related equivalent electrical circuit are extracted and presented, in order to support the design of sensor systems.
In conclusion, the relatively high Q factors at elevated temperatures and the relatively low temperature dependence of the resonant frequencies make CTGS a good candidate for high-temperature gas and temperature sensors.

Recently, various types of oxide nanosheets have prepared by using soft chemistry and reported magneto-optical, high dielectric and photochemical properties by its quantum size effect. However, oxide nanosheet including Zn element didn&’t obtained because Zn element solved out from base material when the oxysalt was ion exchanged by acid aqueous solution such as hydrochloric acid.
In this study, we show newly process for obtaining Zn_0.2Ti_0.8O₂ nanosheet prevented Zn dissolution. Starting materials for Zn_0.2Ti_0.8O₂ nanosheet used lepidocrocite-type K_0.8Zn_0.4Ti_1.6O₄ obtained by solid state reaction method. In ionic-exchange reaction, use of hydrochloric acid showed solve out both of K and Zn elements from K_0.8Zn_0.4Ti_1.6O₄. On the other hands, use of acetic acid in ionic exchanging was able to obtain H_0.76K_0.05Zn_0.39Ti_1.60O4_1.17H₂O. The optimum condition of ionic-exchange reaction was the following; acetic acid 1 mmol / L, 500 mL.
Then, the ionic-exchanged H_0.76K_0.05Zn_0.39Ti_1.60O4_1.17H₂O was performed acid-base reaction by soaking aqueous solution of tetrabutylammonium (TBAOH) at room temperature. After acid-base reaction, colloidal solution was obtained and showed typical UV-Vis spectrum derived from nanosheet. Furthermore, a difference of absorption position for the residual amount of Zn nanosheet was observed from UV-Vis spectrum. From chemical composition analysis using ICP, aggregate restacked nanosheets remaind Zn element after exfoliated as Zn_0.2Ti_0.8O₂ nanosheets. From these results, our newly process is promising method for obtaining the Zn contained oxide nanosheet with various crystal structures.

Acceptor-doped barium zirconate and barium cerate are the promising candidates as solid electrolytes for protonic ceramic fuel cells. Yttrium-doped barium zirconate shows sound chemical stability and excellent proton conductivity at the bulk while its proton conductivity at grain boundaries is poor due to existence of resistive grain boundaries in polycrystalline samples. Contrary to yttrium-doped barium zirconate, yttrium-doped barium cerate shows poor chemical stability but relatively good proton conductivity at both grain boundaries and the bulk. In order to evaluate differences between their grain boundary properties, the Σ3 tilt grain boundaries in barium zirconate and cerate were investigated by using density functional theory. Low proton conductivity at grain boundaries can be evaluated via the space charge layer model and structural disorder model. In barium zirconate, a positively charged oxygen vacancy and proton were segregated at the grain boundary core with segregation energies in the range of -0.52 ~ -0.62 eV and -0.71 ~ -0.82 eV, respectively, indicating positively charged grain boundary core and generation of its Schottky barrier. In barium cerate, however, there was no clear segregation tendency of the oxygen vacancy. However, the proton was segregated at the grain boundary core with segregation energies in the range of -0.36 ~ -0.52 eV, which were less than those in barium zirconate. Therefore, compared with the case of barium zirconate, lower Schottky barrier at the grain boundary core was expected in barium cerate. Further investigations via structural disorder model were performed by calculating energy barrier for proton migration across their grain boundaries.

Recent research into nitridometalates of transition metals containing carbon provided a wide variety of compounds including carbodiimides (e.g. (Sr₆N)[CoN₂][CN₂]₂ [1]), cyano-nitrido-metalates (e.g. Ba₂[NNi(CN)] [2]), and highly reduced cyanometalates (e.g. Ba₃[Co(CN)₃] [3]). Physical properties investigations of these low-valency compounds are challenging due to magnetic impurities like Co or Ni as a result of the synthesis of these phases from the elements and binary nitrides at high reaction temperatures.
In the course of these investigations, the ternary systems AE-C-N (AE = Ca, Sr, Ba) were reinvestigated in detail. Besides the carbodiimides AE[CN₂] [4], the carbodiimide nitrides Ca_4-xSr_x[CN₂]N₂ (AE[CN₂]#9679;AE₃N₂) and Ca₁₁[CN₂]₂N₆ (2Ca[CN₂]#9679;3Ca₃N₂) [5] could be identified. Predominant structural features of both the latter phases are 3D-networks of NAE₆ octahedra sharing common edges and vertices; the carbodiimide anions are located within channels of the octahedral frameworks.
Single phase powder samples of the new compounds Sr₅[CN₂]₂N₂ (2Sr[CN₂]#9679;“Sr₃N₂”) and Ba₅[CN₂]₂N₂ (2Ba[CN₂]#9679;“Ba₃N₂”) were prepared from mixtures of the respective binary nitrides AE₂N and C in the molar ration 2.5 : 1 annealed under nitrogen (oxidizing conditions) at 1250 K and 1000 K, respectively.
The crystal structure of Sr₅[CN₂]₂N₂ (P2₁2₁2 (# 18), a = 1703.13(12) pm, b = 1384.31(9) pm, c = 385.58(2) pm) contains corrugated layers of edge- and vertex-sharing NSr₆ octahedra; the carbodiimide ions are located between these layers.
In contrast, the topology of Ba₅[CN₂]₂N₂ (C2/m (# 12), a = 1362.44(8) pm, b = 413.10(3) pm, c = 956.48(7) pm, β = 100.082(6)°) is based on layers of exclusively edge-sharing octahedra NBa₆. Ba₅[CN₂]₂N₂ is isotypic to La₅[BN₂]₂N₂ [6].
The carbodiimide anions in both compounds are strikingly similar, bond lengths C-N (123-124 pm) and vibration frequencies nu;_u (1933-1956 cm^-1) correspond well with other carbodiimides [4].
Using carbodiimide-nitrides, it is possible to synthesize the above-mentioned low-valency compounds at significantly lower temperatures resulting in products with much lower impurity levels.
References:
[1] J. K. Bendyna, P. Höhn, W. Schnelle, R. Kniep, Sci. Technol. Adv. Mater. 2007, 8, 393.
[2] P. Höhn, R. Kniep, Z. Anorg. Allg. Chem. 2010, 636, 2104.
[3] P. Höhn, F. Jach, B. Karabiyik, Yu. Prots&’, S. Agrestini, F. R. Wagner, M. Ruck, L. H. Tjeng, R. Kniep, Angew. Chem. Int. Ed. 2011, 50, 9361.
[4] N. G. Vannerberg, Acta Chem. Scand. 1962, 16, 2263; U. Berger et. al., J. Alloys Comp. 1994, 206, 179; W. Liao et al., Acta Crystallogr. E2004, 60, i124; M. Krings et al., Chem. Mater. 2011, 23, 1694.
[5] P. Höhn, R. Niewa, R. Kniep, Z. Kristallogr. NCS2000, 215, 323; O. Reckeweg et al., Angew. Chem. Int. Ed. 2000, 39, 412; Z. A. Gal et al., Acta Crystallogr. E2005, 61, i221.
[6] H. Jing et al., Z. Anorg. Allg. Chem. 2000, 626, 514.

During the last decade, the (Li,Na)2M[PO4]F (M= Mn-Ni) fluorophosphates have attracted much attention due to their potential use as positive electrode material in either Li-ion or Na-ion cells. Recently, our research group started systematic studies on the crystal/electronic-structures and the magnetic/electrochemical properties of the intermediate phases LiNaM[PO4]F (Table I).[1-5]
All the samples have been synthesized using solid state reaction route and the single crystals have been grown using salt fluxes. The crystal structures have been determined using the combination of powder neutron diffraction- and X-ray single crystal-data. The magnetic properties were characterized by magnetic susceptibility, specific heat and neutron powder diffraction measurements and also by density functional calculations. The electrochemical properties were characterized by galvanometric, and voltammetric cycling measurements.
During the MRS meeting, the crystal structures of the Li2-xNaxM[PO4]F (M = Mn-Ni, and Mg) compounds will be reviewed. The influence of the size of the transition metal and the Na/Li molar ratio on these crystal structures will be discussed. The relationship between the different structures and their physical properties will be detailed (for more details see ref. [1-5]).
Table I. Crystallographic data of our new compounds.
Formula S. G. a (Å) b (Å) c (Å) V (Å3) ref.
Li1.3Na0.7Ni[PO4]F Pnma 10.7874 6.2196 11.1780 749.97 [1]
LiNaCo[PO4]F Pnma 10.9334 6.2934 11.3556 781.36 [2]
LiNaFe[PO4]F Pnma 10.9851 6.3686 11.4343 799.94 [3]
Li1.65Na0.35Fe[PO4]F Pnma 10.5108 6.4996 11.0504 754.92 [4]
LiNaFe0.75Mn0.25[PO4]F Pnma 10.9719 6.3528 11.4532 798.31 [5]
Li2Mg[PO4]F Pnma 10.5773 6.2378 10.9297 721.10 [*]
Formula S. G. a (Å) b (Å) c (Å) β (°) V (Å3) ref.
LiNaNi[PO4]F P21/c** 6.7720 11.1540 5.0210 90.00 379.26 [1]
LiNaMg[PO4]F P21/c** 6.8179 11.2234 5.0222 90.00 384.30 [*]
Na2Mn[PO4]F-new P21/c** 6.8654 11.8753 5.30702 90.00 432.70 [*]
Na2Ni[PO4]F P21/c 13.4581 5.1991 13.6978 120.58 825.14 [1]
*: to be published
**: Pseudomerohedrally twinned structures
Acknowledgement
Part of this work was financially supported by the Japan Society for the Promotion of Science (JSPS) in Japan.

References
[1] H. Ben Yahia et al., Dalton Trans. 41 (2012) 5838-5847.
[2] H. Ben Yahia et al., Inorg. Chem. 51 (2012) 8729-8738.
[3] H. Ben Yahia et al., Dalton Trans. 41 (2012) 11692-11699.
[4] H. Ben Yahia et al., J. Power Sources (2013), 10.1016/j.jpowsour.2013.03.128.
[5] H. Ben Yahia et al., Mater. Chem. Phys. (2013) 10.1016/j.matchemphys.2013.04.022.

Ceria-based materials offer a low-cost, Earth-abundant alternative to precious metals for the oxidation of carbon monoxide at near-ambient temperatures.[1] Traditionally, transition-metal substituted ceria catalysts have been prepared by impregnation and co-precipitation techniques, leading to polydispersity in crystallite size and the formation of multiple phases, complicating any conclusions about the active-site for CO oxidation catalysis.[2] The pyrolysis of organometallic reagents in surfactant solutions offers a unique way to prepare phase-pure, monodisperse ceria-based materials with tunable crystallite sizes and geometries.[3] We have developed a simple and generalizable synthetic route towards phase-pure, monodisperse (d = 3.0 ± 0.5 nm) transition-metal substituted ceria crystallites (M0.2Ce0.8O2-x, M = Mn, Fe, Co, Ni, Cu) in order to elucidate the structure and role of the transition-metal species in these materials for CO oxidation catalysis. In conjunction with powder X-ray diffraction (PXRD) and high-resolution transmission electron microscopy (HRTEM), X-ray absorption spectroscopy (XAS) demonstrates that the transition-metal species exist as small metal-oxide clusters on the [111] and [100] surfaces of CeO2 truncated octahedra. The low-temperature CO oxidation activity for M0.2Ce0.8O2-x demonstrates a clear trend with transition-metal substitution; catalysis is a function of the reducibility of the transition-metal, with enhancement originating in more reducible transition metal species such as Cu(III).
References:
1. Liu, W.; Flytzani-Stephanopoulos, M. Journal of Catalysis 1995, 153, 304.
2. Gamarra, D.; Munuera, G.; Hungria, A. B.; Fernandez-Garcia, M.; Conesa, J. C.; Midgley, P. A.; Wang, X. Q.; Hanson, J. C.; Rodriguez, J. A.; Martinez-Arias, A. J. Phys. Chem. C 2007, 111, 11026.
3. Lee, S. S.; Zhu, H.; Contreras, E. Q.; Prakash, A.; Puppala, H. L.; Colvin, V. L. Chem. Mater. 2011, 24, 424.

Recently there is enormous growth in the research work towards renewable energy sources that do not rely on petroleum. While solar cell technology has been investigated for many years, the traditional materials developed in this area still have many drawbacks that must be addressed. For example, the cost of the fabrication technology of the solar cell modules, or the abundance of the constituent elements are still concerns. Cu(In,Ga)Se2(CIGS)nanoparticles are a good example of the chalcogenide based semiconductors that have been proposed as one of the highly efficient and low-cost photoelectric conversion materials, yet indium and gallium are relatively rare in abundance while creating the material is energy intensive. CuZnS nanoparticles however are composed of abundant elements, can be created in a straightforward chemical synthesis reaction, and have the potential to display enhanced and controllable photovoltaic properties. To study the properties of this class of nanomaterial, we first synthesized CuZnS nanoparticles with a controllable composition and structure by utilizing the well-known thermolysis reaction. Next we characterized these nanoparticles in terms of their physical and optical characteristics. The results reveal a unique correlation between the nanoparticle composition/structure and the exhibited photovoltaic properties. The presentation will relate the results of our recent studies in the synthesis and characterization of CuZnS nanoparticle materials for semiconductor applications. The results will be discussed using characterization techniques such as XRD, XPS, TEM, STEM-HAADF, EDS Elemental Mapping and others.

I will describe our work on the design and discovery of new classes of antiferroelectric materials using a combined crystallographic database / high-throughput first-principles approach. Using a design principle based on the close relationship between ferroelectrics and antiferroelectrics, we have identified a previously unrecognized class of antiferroelectrics, related to the LiGaGe-type ferroelectrics, in the MgSrSi structure type. This search strategy has been extended to target antiferroelectrics with desirable functional behavior arising from contrast in properties of the zero-electric-field and electric-field-induced phases, and preliminary results will be presented. The discovery of new classes of antiferroelectrics is expected to open the way to increased recognition and application of antiferroelectrics as functional materials.

Details of atomic coordination and dynamics in the solid state are often key aspects of functional materials. Here we will explore selective gas adsorption at active sites in metal organic frameworks and ion intercalation and diffusion in insertion electrodes for batteries. Extracting information on these processes at the atomistic level is possible using core-level spectroscopy. X-ray Absorption Spectra (XAS) are direct measurements of element-specific electronic structure of materials and are exquisitely sensitive to the symmetry of atomic coordination and bonding. Frequently, however, such measurements on complex systems defy interpretation. We have developed a density-functional-theory-based first-principles computational tool-kit to simulate XAS at elemental K-edges (1s excitations), which explicitly incorporates intrinsic degrees of freedom at finite temperature via molecular dynamics sampling, accurately reproducing experiment in systems of known atomic and electronic structure. With this approach we highlight examples in energy-relevant materials and processes in which XAS provides a particularly sensitive probe of changes in coordination and dynamics of specific atoms in a solid-state context. We interpret spectral changes in certain specific materials as indicative of: the strength of bonding to undercoordinated atomic sites in porous crystals; intrinsic finite temperature dynamics which favors broken crystal symmetry; and the degree of anisotropy and localization of neutralizing electron density about intercalated cations.

The extreme shortage of ³He, used in neutron detectors, has caused a crisis for scientists around the world. To handle the crisis, the boron isotope ¹⁰B has been proposed for the replacement due to its neutron absorption cross-section comparable to that of ³He. Among boron and its compounds, boron carbide, B₄C, is the most promising material for new types of neutron detectors [1]. It is not only non-toxic, chemically and thermally stable, but it can also be synthesized in the form of thin solid films using physical vapor deposition making possible its usage in cost-efficient high quality neutron detectors. Boron carbide has also possible applications as a chock-resistant material and for high-temperature thermoelectrics. For the development of these applications a detailed understanding of boron carbide on the atomic level is needed. Unfortunately, the structure of boron carbide has not been fully understood because of its very complex atomic arrangement including both 12-atom icosahedras with polar and equatorial sites and 3-atomic chains in the unit cell and a possibility for boron-carbon configurational disorder [2]. In this work, we use first-principles calculations to investigate phase stability and properties of the stoichiometric compound B₄C, when point defects as well as various degrees of configurational disorder are introduced. We start with making an extensive survey of 15 point defects involving in particular all types of site displacement of the icosahedral carbon atom. Our results confirm previous more limited investigations [3] that two types of a single atom defect, i.e. 1) a rotation of a carbon atom among the polar up-sites in an icosahedral structure, and 2) a bipolar defect (B₁₀C₂+B₁₂), are the most likely defects to be presented in boron carbide during the process of synthesis. From this results we move further and suggest a new method to distribute high concentrations of these two types of defects in boron carbide in a disordered manner. It is based on combining the special quasi-random structure (SQS) technique with a concept of super-atoms of different icosahedral structure. In this way the properties of B₄C as it is configured at high temperature or in out-of-equilibrium thin films can be directly calculated with supercells thus bringing theoretical predictions one step closer to the real situations. Supercell sizes up to 540 atoms have been used in the calculations. As an example, we found that disordered B₄C with a random distribution of icosahedral carbon atoms among the polar up-sites, has the rhombohedral symmetry as it is for the carbon poor B₁₃C₂ compound. The transition temperature from the perfectly ordered phase to the disordered phase is 770 K, within the mean-field approximation for the entropy.
[1] C. Höglund, et al., Journal of Applied Physics, 111, 104908 (2012).
[2] V. Domnich, et al., J. Am. Ceram. Soc., 94, 3605 (2011).
[3] M. Widom, and W. P. Huhn, Solid State Sciences, 14, 1648 (2012).

Predicting whether and in what crystal structure a compound forms knowing only the elemental components and without constraints on the lattice vectors and atom positions, is a central problem in Solid-State Chemistry. Solving this problem requires a global space-group optimization (GSGO) of the total energy of a solid as a function of the crystal degrees of freedom. Evolutionary algorithms are powerful global optimization methods, and I will describe the implementation of such an algorithm coupled to a state-of-the-art ab initio total-energy method that successfully addresses the GSGO problem of predicting the stable crystal structure of solids (Ref. 1). I will then introduce the X-GSGO extension of the algorithm to predict the compositions (Ref. 2), as well as the crystal structures, of the thermodynamically stable phases of a solid system, starting from the elements that compose it. I will discuss the application of the evolutionary GSGO method to selected materials systems:
1. Metallic alloys such as Al-Sc are difficult ground-state search problems for the standard cluster expansion method as the underlying lattice is difficult to fix knowing only the elemental components. The X-GSGO algorithm retrieved the compositions and crystal structures of all the Al-Sc compounds (Ref. 2) that possess fcc, bcc, hcp, Laves-phase structure types.
2. In the Na-N system, the previously predicted Na3N compound manifests only heteropolar Na-N bonds and has positive formation enthalpy. Based on the X-GSGO algorithm we predict the first alkali diazenide compound NanN2 (Ref. 3), manifesting homopolar N-N bonds. Na2N2 completes the series of previously known BaN2 and SrN2 diazenides
3. The recent discovery of the C3B and C5B compounds has raised hopes of revealing interesting properties such as superconductivity but also questions about the stability and crystal structure of such compounds. Through the X-GSGO method we find ordered structural models (Ref. 4) for C3B (layered hexagonal) and C5B (diamond-like) with lower energies than previously obtained.
4. We will show applications of GSGO to ternary systems including LiF-CsF, which shows ordering in spite of the large atom size mismatch of the cations, the Ag-V-O system, which has been explored to search for new transparent-conducting oxides, and YBiO3, which has recently been proposed as a new topological insulator but in the hypothetical perfect perovskite structure whose stability is so far unverified.
References:
1. G. Trimarchi and A. Zunger, Phys. Rev. B 75, 104113 (2007).
2. G. Trimarchi, A. J. Freeman, and A. Zunger, Phys. Rev. B 80, 092101 (2009).
3. X. Zhang, and A. Zunger, G. Trimarchi, J. Chem. Phys. 133, 194504 (2010).
4. A. S. Mikhaylushkin, X. Zhang, and A. Zunger, Phys. Rev. B 87, 094103 (2013).

Differences between the local and average structures, even subtle ones, often control the exploitable properties of advanced materials. Therefore, determination of the local atomic arrangements is key to establishing structure-property relations for the design of new materials. Today, various measurement techniques exist for probing the local atomic order. Nonetheless, finding accurate comprehensive structural solutions still remains a challenge because any one of the existing methods yields only a partial view of the structure. We addressed this problem by developing a computational framework for local-structure determination in polycrystalline materials using simultaneous fitting of neutron total scattering, X-ray absorption fine structure, and single-crystal diffuse scattering data. The multiple-technique approach enables explicit determination of instantaneous atomic positions with accuracy and detail that are inaccessible by single-technique analyses. We will use representative perovskite-like electroceramic systems as examples of how detailed knowledge of the local structure can elucidate the origin of functional properties.

The aim of the presentation is to show how to use the bond valence model as a predictive law to easily establish some structural parameters in inorganic oxides. Three examples will be presented. The two first examples deal with würtzite structures, the last example with perovskite structure.
In the first one, different sets of ZnO Nano-Crystallites, with well controlled crystallite size within the range 7 nm - 40 nm, were synthesized in a various polyol media, at various temperatures. X-ray diffraction refinements clearly showed an asymptotic decrease of both a and c cell parameters versus the crystallite diameter. These evolutions can be ab initio predicted using the bond-valence model to calculate the various bond lengths from the surface to the bulk of the crystallites.
The würtzite-type ionic compounds exhibit flattened tetrahedral sites with a significant decentering of the central atom along the z axis. These structural features depend on the chemical composition. It is very well known but until now, not fully explained. First, we showed that anisotropic vibrations are the cause of the tetrahedral sites flattening in standard würtzite compounds. Then, we proposed a model consisting in the minimization of the cell volume but respecting in the same time the bond valence model, i.e. each couple of atom and its associated bond has to respect the bond valence law. This model is a new way to predict the tetrahedral distortion and especially the würtzite universal relationship between the z atom parameter (ions decentering) and the c/a ratio (cell-tetrahedral distortion).
The prototypical ferroelectric system BaTiO3 is an oxide with a perovskite-type structure that exhibits a textbook example of multiple phase transitions associated with an out-of-centre distortion of the octahedral Ti4+ cations. Numerous investigations on the BaTiO3 transitions parameters: Ti4+ displacement, cell parameters evolution, transition temperatures have been studied in an extended way in literature. Recently, it is clear that first-principles calculations integrating molecular-dynamics simulations have allowed getting satisfying understanding of the phase transitions in this system. Nevertheless, all the calculations based on the construction of modified Hamiltonians constitute a barrier for a simple conceptualization. We show that combining two simple “chemist” models: the double-well potentials model and the bond valence model, it is possible to provide a new and simple description for the cubic-tetragonal-orthorhombic-rhombohedric phase transition sequence.
The three presented ab initio calculations all based on bond-valence model: (i) can be reproduced by any solid state chemist (the calculations can be made with a pen), (ii) the number of inset parameters is incomparably low besides first-principles DFT calculations, (iii) show that the respect of the bond flux in ionic inorganic compound is very preponderant on the crystalline structuration.

The 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]. In parallel with experimental efforts, computer-aided materials design is also an important factor in the analysis as well as in the fabrication of novel materials. The high sorption ability for acetylene on MOF material (Cu2(pzdc)2(pyz)) was determined [2], using both different experimental measurements and extensive first-principles calculations which ascribe to the double hydrogen bond support between the acidic acetylene proton and its acceptor basic site on the channel surface. In order to evaluate the parameters of weak interactions, a time-dependent density-functional formalism and local density technique entirely in real space have been implemented for calculations of vdW dispersion coefficients for atoms within the all-electron mixed-basis approach [3]. The obtained vdW dispersion coefficients allow us to calculate the amount of adsorbed gas inside MOF structures in various ranges of pressures and temperatures.
Here, our recent results related to the first-principles estimation of the guest-host interactions inside specific MOF structures will be presented. 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 storage and separation. The specific nano-porous material that selectively adsorbs CO with adaptable pores has been studied using first-principles calculations. The high selectivity of CO has been achieved from a mixture with nitrogen by both the local interaction between CO and accessible Cu²⁺ metal sites and the modification of nano-pore size. The obtained results have been compared with CO adsorption into HKUST-1 structure.
REFERENCES
[1] S. Kitagawa et al., Angew. Chem. Int. Ed. 43 (2004) 2334.
[2] R. Matsuda et al. Nature 436 (2005) 238.
[3] R. V. Belosludov et al., in: Lee K-M, Kauffman J (eds). Handbook of Sustainable Engineering. Springer, New York, (2013) pp 1215-1247.

The oxidation of metals plays a critical role in many technologically important processes including high-temperature corrosion, heterogeneous catalysis, and fuel reactions. Oxygen surface chemisorption is believed to occur at the very initial stage of the oxidation reaction, which induces consecutive surface reconstructions as the oxygen coverage increases. Among various chemisorptions systems, oxygen on Cu(110) surface has provided a model chemisorptions system involving oxygen adsorption and interdiffusion of Cu and O. The behavior of oxygen chemisorption induced phase transition of Cu(110) upon oxygen exposure has been studied extensively. However, an atomistic understanding of the dynamical process of the phase transition is still largely lacking. In this work, we employ density functional theory (DFT) and kinetic Monte Carlo (kMC) methods to dynamically simulate the phase transition from the clean Cu(110) surface to (2×1)-O reconstructed phase. Our model successfully describes the interactions between Cu and O atoms and reproduces the reconstructed surface phase. Our results agree very well with the experimental observations under various oxidation conditions. We expect that our proposed methodology can be further utilized to dynamically simulate the early-stages of oxidation of other systems, and the extension of the insights obtained from this study to understand the oxidation process of transient metals will be discussed.

Periodic patterns shown by crystal structures, melting points, and electrical conductivity of the transition metals are not well explained by existing theories. A model of electronic structures for solid transition metals in groups 3 to 11 provides some qualitative insights into these patterns. It is based on two standard approaches: (1) overlaps of atomic orbitals for large systems lead to energy bands and (2) hybrid atomic orbitals can be generated to give bonding with specific geometric orientations. For each of the three dominant crystal structures - bcc, hcp and fcc - a different set of hybrid orbitals is chosen. By using symmetry, an energy template is determined for each of these structures. The template serves as the basis for an aufbau approach, assigning electrons to bands in specific ways. Qualitative arguments then link these assignments to the rise and fall of melting points across three rows of transition metals, the observed crystal structures, and other periodic properties.

Recent progress in understanding electronic wave functions in condensed matter nanostructures has led to an ability to synthesize isolated, quantum confined building blocks with a variety of tailored optical properties. No matter what optical gap is engineered and how cleverly exciton energy is redistributed, though, novel materials composed of such nanostructures need to also exhibit efficient carrier dynamics. Transport of energy and charge is now the central issue in harnessing the true power of quantum dot materials for solar and many other uses. This is a critical bottleneck in the science because charge and exciton transport tend to proceed via low mobility, incoherent hopping associated with weak electronic coupling and high reorganization energies in these nanostructures.
A number of promising strategies seek to improve energy and charge transport between quantum dots by focusing on important properties such as translational symmetry, electronic overlap, matrix encapsulation, and crystalline orientation. Our approach, though, is to consider the entire assembly as a quantum dot mesomaterial (QDM), wherein entirely new transport physics may emerge from the complex interactions between components. For instance, the superb exciton harvesting efficiency of photosynthetic complexes is at least partly due to conditions that support an element of coherent character for exciton transport. Here proteins and pigments are exquisitely structured and combined so that they perform a number of integrated functions—e.g. proteins serve to correlate electronic excitations on neighboring pigments, supporting coherence and allowing exciton transport with a degree of wave-like character.
We seek to design materials composed of quantum dots in which components may carry out integrated tasks that optimize dynamics ranging from incoherent random walks to coherent transport. An emphasis is placed on the robustness of such transport in the face of geometric uncertainties intrinsic to synthesized systems.
The computational facet of our investigation, emphasized in this talk, utilizes an open dissipative system approach, wherein a cumulant expansion strategy is used to approximate the quantum Liouville equation via a hierarchy of density operators. This has been successfully employed to scrutinize partially coherent transport in protein/pigment complexes, but here we focus on silicon quantum dot mesomaterials and use excited state many-body calculations to populate the associated meta-Hamiltonian. After an overview of the mesomaterial perspective, this talk will focus on our computational assessment of the prospects for partially coherent exciton transport through these silicon quantum dot mesomaterials.

Colloidal semiconductor quantum dots (QDs) are attractive building blocks for solar photovoltaics (PV). In this talk, I will provide an overview our ongoing efforts to design lead salt QD thin film absorbers for next-generation PV. Basic requirements for QD absorber layers include efficient light absorption, charge separation, charge transport, and long-term stability. I will first discuss several methods used to make conductive QD films by solution deposition and ligand exchange. Studies of carrier mobility as a function of basic film parameters such as inter-QD spacing, QD size, and QD size distribution have led to a better understanding of charge transport within highly disordered QD films. Efforts to improve carrier mobility by enhancing inter-dot electronic coupling, passivating surface states, and implementing rudimentary doping will be highlighted. Engineering the inter-QD matrix to produce QD/inorganic or QD/organic nanocomposites is introduced as a promising way to optimize coupling, remove surface states, and achieve long-term environmental stability for high-performance, robust QD films. To obtain large photocurrent from QD solar cells, it is critical to increase the minority carrier diffusion length to rival the optical absorption length, possibly by harnessing band-like transport through extended electronic states. The relative roles of superlattice order, energy disorder, and surface states in this regard will be summarized. The talk will conclude with comments on the prospects for controlled doping and rational p-n junction formation in QD systems.

The significant number of missing materials that are not reported in literature but potentially thermodynamically stable offer a fruitful arena for high-throughput design of new functional materials. It is found that 75% (888) of the ABX compounds are missing in the following 12 groups with 8 or 18 valence electrons: I-I-VI (e.g., CuAgSe), I-II-V (e.g., AgMgAs), I-III-IV (e.g., LiAlSi), II-II-IV (e.g., CaZnSn), I-X-VII, II-X-VI, III-X-V (e.g., LaPtBi), IV-X-IV (e.g., TiNiSn), II-IX-VII, III-IX-VI, IV-IX-V (e.g., HfRhSb), and V-IX-IV (e.g., NbCoSn). We use high-throughput first-principles thermodynamics to search the lowest-energy structure and evaluate all the possible combinations of competing phases for a given ABX. Of the 888 missing ABX we find that 577 are unstable with respect to decomposition into different types of competing phases for different chemical groups and 289 are predicted to be stable (22 are too close to call). We next add the missing, but predicted stable ABX compounds to the list of previously known stable ABX, thus creating a complete list from which chemical trends in properties can be reliably assessed, e.g., (V, Nb, Ta) (Co, Rh, Ir) (Si, Ge) are metallic except the heaviest compound TaIrGe. We characterize the potential functionalities of the new stable ABX compounds, including topological insulator (TI), photovoltaic (PV) absorber, transparent conductor, thermoelectric, and spintronic behavior. For example, NaCaBi is predicted to be a wide gap (~0.5 eV) TI, the three-metal semiconductor KYPb has high PV absorptivity, TaIrGe is a candidate transparent conductor, and HfPtSn has very large Dresselhaus spin splitting. A number of new compounds, e.g., TaCoSn, TaIrGe, HfIrSb, have been realized experimentally in the predicted structures using bulk fabrication methods, including arc melting, powder metallurgy, and microwave sintering, as well as thin film techniques, including combinatorial sputtering and thermal evaporation. The measured band gaps and transparent conductivity in TaIrGe are in good agreement with theoretical results. Experimental realization of these materials demonstrates that theoretical prediction is key to identifying stable missing materials and in providing accurate information about the symmetry of these crystal structures. This latter information is critically important to accelerate the characterization of any newly made phase. This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Energy Frontier Research Centers, Center for Inverse Design.

n the monolayer limit, transition metal dichalcogenides become direct-bandgap, light-emitting semiconductors. The quantum yield of light emission is low and extremely sensitive to the substrate used, while the underlying physics remains elusive. In this work, we report over 100 times modulation of light emission efficiency of these two-dimensional semiconductors by physical adsorption of O2 and/or H2O molecules, while inert gases do not cause such effect. The O2 and/or H2O pressure acts quantitatively as an instantaneously reversible “molecular gating” force, providing orders of magnitude broader control of carrier density and light emission than conventional electric field gating. Physisorbed O2 and/or H2O molecules electronically deplete n-type materials such as MoS2 and MoSe2, which weakens electrostatic screening that would otherwise destabilize excitons, leading to the drastic enhancement in photoluminescence. In p-type materials such as WSe2, the molecular physisorption results in the opposite effect. Unique and universal in two-dimensional semiconductors, the effect offers a new mechanism for modulating electronic interactions and implementing optical devices.1
1 Nano Lett. 2013, 13, 2831.

Dye sensitized solar cells (DSSC) have been attracting attention since their invention. Low-cost production and moderate efficiency values obtained in these cells are main advantages of the DSSCs, however commercialization requires higher efficiency values. Strategies for improved efficiencies include high performance sensitizers, novel hole conductors and different anode material architectures. Application of transition metal oxides other than TiO₂ like SnO₂, Nb₂O₅, ZnO and ZrO₂ have been tried by many researchers but none of them can compete with TiO₂. SnO₂ is a promising candidate DSSC anode material as it provides higher electron mobilities compared to TiO₂. Its electronic properties can be tailored upon doping with fluorine or antimony. However, cells made from SnO₂ suffers from high recombination rates. One strategy to solve this problem is the modification of SnO₂ surface with other metal oxides and create an energy barrier for suppressed recombination referred as core-shell type anodes. Fluorine doped tin dioxide (FTO) is a well-known TCO material used in conductive substrates in DSSCs. In this work, nanoparticles of FTO were produced by a hydrothermal method and used as core material in DSSCs having a particle size around 15 nm and high specific surface area (55 g/m²). Fluorine content of the particles was determined to be around 0.4% at. from XPS and electrical resistivity down to 17 ohm.cm could be achieved. Thin shell coatings of Al₂O₃, MgO, ZnO, TiO₂ and ZrO₂ were deposited on the screen printed anode by chemical bath deposition in order to enhance the performance of the DSSCs constructed from FTO nanoparticles. Core-shell mesoporous anode of the electrically conducting FTO core and a shell of different metal oxides were produced and amount of enhancement of each shell material on the DSSC performance was investigated in comparison with pure TiO₂ and SnO₂. It was observed that both open circuit voltage and short circuit current of the SnO₂ anode can be enhanced by doping with fluorine due to the increased Fermi level and improved electronic conduction and efficiency was enhanced from 0.8% to 1.16%. Modification of the FTO matrix with outer shell materials resulted in further enhancement for all metal oxides. The improvement was attributed to increased charge transfer resistances originating from the suppressed recombination of the layers acting like energy barriers which was confirmed by electrochemical impedance spectroscopy. Best results were obtained with cells where shell material is TiO₂ giving an efficiency value of 4.74% which was attributed to the unique increase of each cell parameters where metal oxides with high conduction band edge potentials mainly cause poor electron injection efficiencies yielding low current densities, although open circuit voltages and fill factors are improved compared to uncoated FTO nanoparticles.

This presentation will describe our recent and cumulative results on the use and operation of electrochemical liquid-liquid-solid (ec-LLS) processes for the preparation of crystalline semiconductor materials. Through ec-LLS, the possibility exists to prepare directly crystals of important group IV and III-V semiconductors at low, non-energy-intensive conditions. The ec-LLS tactic combines the traditional features of electrodeposition with flux crystal growth strategies through the use of liquid metal electrodes.
The emphasis of this talk will be to provide insight on how the relative rates of the involved chemical, electrochemical, and transport steps impact the resultant quantity and quality of crystalline material. Results from electrochemical experiments performed in aqueous electrolytes under ambient conditions as well as in non-aqueous solvents under elevated pressure/temperature conditions will be detailed. The ability to grow high quality single crystals in this manner will be discussed.

Colloidal III-V quantum dots (QDs) are attractive as visible emitters for lighting and display technology (InP) or highly stable infrared fluorophores for deep tissue in-vivo imaging (InAs). However, these materials have proven more challenging to synthesize with the narrow size distributions that are readily obtained using II-VI and IV-VI materials such as CdSe and PbSe. The superior size distributions of II-VI and IV-VI materials can be explained by the size focusing that occurs as molecular precursors react and add to growing nanocrystals. In contrast, the III-V precursors react quickly, and particles grow in the absence of molecular precursors.
We set out to synthesize and characterize less reactive molecular precursors for the synthesis of III-V quantum dots. By making modest changes to the phosphorous and arsenic precursors used in the currently optimized procedures that people currently rely on, we ensure chemical compatibility with the solvent and ligand systems that have been successfully used for high quality nanocrystal growth. We show that we are able to dramatically slow precursor conversion rate while still using the same group III precursor, solvent, and ligand system.
By systematically comparing the effects of different chemical substituent groups on precursor conversion rate and nanocrystal particle size distribution, we provide a platform to quantitatively test theories of how precursor conversion rate affects ensemble particle size distribution and we reveal opportunities to improve synthetic control over QD formation by tuning precursor reactivity.

In compounds with direct metal-metal bonds the lifting of typical d-orbital degeneracies can give rise to unusual electronic structures and physical properties when compared to those compounds without such bonds. The crystal structure, electronic structure, magnetic properties, and optical properties of both known and novel molybdate structures with direct metal-metal bonding have been studied. Novel structures were determined from high resolution powder diffraction data (both X-ray and neutron, with d_min~0.3 Å) using a combination of charge flipping and Fourier difference map methods, allowing different types of 1D polyhedral chains to be observed. Accurate information about Mo-Mo and Mo-O bonding was obtained through Rietveld refinement of neutron diffraction data collected over a wide temperature range (10-1200 K) to determine whether thermal excitations in these small band gap semiconductors (E_g ~ 0.5 eV) leads to strongly anisotropic changes in bonding. Molecular orbital analogies are made to the band structure of these compounds calculated from DFT to assess bond order and the nature of the chemical bonds in these systems.

The development of improved characteristics of functional nanoscaled devices involves novel materials, more complex structures and advanced technological processes, requiring analytical methods to be well adapted to the nanoscale. The transitions to heavier elements in current nanoelectronics and to thick cap layers restrict access to the analysis of the interfaces determining the device properties. Thus, non-destructive and non-preparative techniques for chemical nanometrology providing sufficient sensitivity, reliable quantification and high information depths to reveal interfacial properties such as chemical species and related mass deposition are needed for an interfacial analysis.
Appropriate measurement strategies adapted to a nanoscaled stratified sample enables the combined technique of Near-Edge X-ray Absorption Fine Structure (NEXAFS) and Grazing Incidence X-ray Fluorescence (GIXRF) to provide interfacial species information. GIXRF-NEXAFS is a non-destructive and non-preparative technique which has the advantage that the interfacial chemical bonds remain unchanged by the measurement.
The validation of this method for interface speciation has been performed at nano-layered model structures consisting of a Si substrate, a physically vapor deposited Ni metal layer and, on top, a chemically vapor deposited B_xC_yN_z light element layer. The chemical bonds in the interfaces were to be determined by the GIXRF-NEXAFS technique. B. Pollakowski et al., Anal. Chem. 85, 193 (2013)

The icosahedral quasicrystals (i-QCs) are 3D aperiodic structures with 5-fold symmetry appearing in a diffraction pattern. Icosahedral quasicrystals are the most represented aperiodic structures with ternary and also binary systems. It is significant that first quasicrystals discovered by Shechtman in Al-Mn system were showing exactly icosahedral symmetry. However there are only few refined i-QCs structures [1-3]. Current models for structure solutions of i-QCs are based on cluster analysis (either in real or in higher-dimensional space).
In this presentation the new approach for structure solution of i-QCs will be presented. The method is based on statistical approach with use of Average Unit Cell (AUC) concept [4]. The AUC is the statistical distribution of projections of considered quasicrystalline lattice nodes onto the periodic reference grid. The distribution is uniform and dense and follows the TAU2-scaling rule [5]. The main advantage of this method is that it works in real space only. It was also shown that the AUC shape is directly related to the shape of atomic surface in higher-dimensional description [6]. Statistical approach has been already successfully applied to decagonal Al-Ni-Co and Al-Cu-TM (TM=Co,Ir,Rh) phases [7,8].
The starting structural model for statistical approach is Ammann tiling, which is just the expansion of Penrose rhombi tiles for 3D case [9]. The structural units in Ammann tiling are prolate and oblate rhombohedra, which volumes ratio is given by golden mean value tau;asymp;1.618. For “empty” Ammann tiling the structure factor was already derived [10] and the agreement of AUC and higher-dimensional description was proved.
Recently the attempts for atomic decoration of rhombohedra was done. The division of atomic surface for regions of rhombohedra of different orientations was carried out. For the derivation of complete structure factor for Ammann tiling, the first trials of decorating the tiles with atoms is performed.
1. L. Elcoro, J.M. Perez-Mato, G. Madariaga, Acta Crystallogr. A50 (1994), p. 182.
2. A. Fang, H. Zou, F. Yu, R. Wang, X. Duan, J. Phys.: Condens. Matter 15 (2003), p. 4947-4960.
3. H. Takakura, C. Pay Gomez, A. Yamamoto, M. de Boissieu, A.P. Tsai, Nature Materials 6 (2007), p. 58.
4. J. Wolny, Philos. Mag. A77, (1998), p. 395-412.
5. J. Wolny, B. Kozakowski, Aperiodic Crystals (2013), p. 125-132.
6. B. Kozakowski, J. Wolny, Acta Crystallogr. A66 (2010), p. 489-498.
7. P. Kuczera, J. Wolny, F. Fleischer, W. Steurer, Philos. Mag. 91 (2011), p. 2500-2509.
8. P. Kuczera, J. Wolny, W. Steurer, Acta Cryst. B68 (2012), p. 578-589
9. P. Kramer, R. Neri, Acta Crystallogr. A40 (1984), p. 580-587.
10. J. Wolny, B. Kozakowski, P. Kuczera, R. Strzalka, A. Wnek, Isr. J. Chem. 51 (2011), p. 1275-1291.

Development of new materials for solid oxide fuel cells (SOFCs) with enhanced electrochemical properties is essential to meet the requirement for low cost, efficient sustainable energy conversion devices. A major driver for enhanced conductivity at lower temperatures is enabling the application of cheaper, more widely available materials for stack construction. The best oxide ion conductivities in the intermediate temperature fuel cell regime (500-700 °C) are usually found in the fluorite type lattice structures, with gadolina doped ceria being particularly notable. However, the lack of progress in improving these materials properties further has led a new search for novel phases in which oxide ion migration may occur at low temperatures. Recently, a novel phase and oxide ion conduction mechanism was reported by Singh and Goodenough [1], claiming oxide ion conductivities of an impressive 10^-2 S cm^-1 at 625 °C in the chemically optimised Sr_0.8K_0.2Si_0.5Ge_0.5O_2.9 composition.
In this work, we report the successful reproduction of the samples as originally described in the Singh and Goodenough publication, with elemental composition characterised by Inductively coupled plasma atomic emission spectroscopy and lattice cell parameters by powder X-ray diffraction. Furthermore, time-of-flight powder neutron diffraction (TOF-PND) has been performed on the best performing oxide ion conducting composition, Sr_0.8K_0.2Si_0.5Ge_0.5O_2.9, to probe the oxygen defect structure.
Interestingly, the material is shown to be markedly hygroscopic in nature hindering simple electrochemical characterisation due to the apparent deleterious effects of the incorporation of water. This work attempts to probe this relationship via controlled experimental technique. Oxygen diffusion profiles have been obtained via ¹⁸O tracer measurements in collaboration with time-of-flight secondary ion mass spectrometry to directly probe the extent of oxygen ion diffusivity in the structure. The Nernst-Einstein relationship is used to correlate oxygen ion diffusivity and total conductivity based on the defect structure determined by TOF-PND, to provide an effective oxygen transference number. Finally, molecular dynamic simulations are attempted to further explore the oxygen ion migration within these structures.
1. Singh, P. and Goodenough, J.B., Sr_1-xK_xSi_1-yGe_yO_3-0.5x: a new family of superior oxide-ion conductors. Energy & Environmental Science, 2012. 5(11): p. 9626-9631.

Ceria is an insulating rare earth metal oxide used for a wide
range of applications including glass-polishing, ceramics, nano-medicine,
solid state electrochemistry, and catalysis, where it can be used as a
catalyst itself} or as a support material. The basis of this
application is the low energy of formation of oxygen vacancies, which
allows the material to absorb oxygen under oxidizing conditions and
release oxygen under reducing conditions.
We present results of density functional theory calculations on the
phonon dispersion and elastic constants of bulk ceria as a function of
positive and negative isotropic strain, which could be induced
thermally or by cationic doping. We find that, as the lattice is
expanded, there is a significant softening of the B_1u mode at the
X-point, which consists of motions of oxygens in the [001]
direction. At a strain of 1.6 %, corresponding to a
temperature of 1600 K, the B_1u and E_u modes at the X-point
cross, with an associated high, narrow peak in the phonon density of
states appearing. We infer that this crossing indicates a coupling of
the modes, leading to a transition to a superionic phase, where
conductivity occurs in the [001] direction, mediated
by anion interstitial site occupation. Expanding the lattice further,
the B_1u mode continues to soften, becoming imaginary at a strain
of 3.4 %, corresponding to a temperature of 2500 K. Following the
imaginary mode would result in a cubic to tetragonal phase
transition. Our calculated elastic constants, however, indicate that
the structure remains mechanically stable, even at this level of
expansion. We confirm that the cubic phase is the most stable using
semiclassical free energy calculations, while the imaginary mode
indicates a change to a thermally disordered phase, with the majority
of disorder occuring in the anion sublattice. Our results explain the
high temperature ionic conductivity in ceria and other
fluorite-structured materials in terms of the intrinsic lattice
dynamics, and give insight to the stability and anionic disorder at
elevated temperatures.
Ref.: J. Buckeridge et al., Phys. Rev. B 87, 214304 (2013)

The structure replication method (nanocasting) is a versatile method for synthesizing mesoporous metal oxides with large specific surface areas, ordered porosity and high crystallinity. During the last decade a large variety of binary metal oxides were prepared by this method, but only few reports have been made for the successful synthesis of mesoporous ternary (multi-metal) oxides. We present the synthesis of mesoporous ordered spinel-type phases, e.g. cobalt oxide (Co₃O₄) and cobalt ferrite (CoFe₂O₄), by nanocasting, using porous silica as a structure matrix. Thus-obtained magnetic materials exhibit specific surface areas of ca. 160 m² g^-1, pore sizes of 4.9 nm, and crystallite sizes of ca. 15 nm.
Combining ferromagnetic ordering with another kind of ferroic property (e.g. ferroelectricity) results in so-called multiferroic phases, which increasingly attract interest in material science and nanotechnology. Our approach for synthesizing such multifunctional materials is to prepare composite materials which consist of the (porous) ferromagnetic phase and a ferroelectric perovskite phase, such as barium titanate (BaTiO₃), incorporated in the pores (or vice versa).
The nanostructured materials show magnetic properties different from those of the respective bulk phases. For example, a clear correlation is observed between magnetic ordering phenomena and such structural properties as the specific BET surface area, crystallite sizes, or grain boundaries. We present a systematic study on these structure-property relations for ferromagnetic as well as antiferromagnetic compounds. These results indicate the suitability of said materials for such application as data storage or sensing.

Diffusion and other slow processes require time-scales that cannot typically be reached in traditional molecular dynamics (MD) or Monte-Carlo simulations. We have developed a general lattice kinetic Monte-Carlo (KMC) code, KMCLib, to address this problem. Employing a multi-scale approach, where individual diffusional rates are calculated with accurate density functional theory (DFT) methods, and where dynamics is propagated by means of KMC, we make a detailed study of oxygen vacancy diffusion in cerium oxide. This lattice KMC approach is very general, and in particular, our code allows one to study bulk and surface diffusion, as well as chemical reactions of heterogeneous catalysis; using either pre-calculated rates, or rates calculated on the fly. Computationally heavy back-end functionally is written in C++, and front-end functionality for performing calculations and analysing data is written in Python. The code is publicly available under the GPLv3 license.

Perovskite oxide nanocrystals with the formula ABO3 (A = Li, Sr, Ba; B = Ti, Zr, Nb, Ta) and their corresponding solid solutions exhibit a wide range of properties that make them promising functional materials in the areas of energy conversion and storage (dielectric spacers in capacitors), display technologies (phosphor hosts in field emission displays), and heterogeneous catalysis (supports for noble metals). The versatility of this family of materials stems from the composition dependence of their physical properties, which allows their functionality to be optimized by fine tuning the chemical composition. In the past, perovskite oxide nanocrystals have been synthesized using energy-intensive methods that rely on the use of physical (heat, pressure) and chemical (surfactant, mineralizer) agents to achieve a crystalline oxide product. In addition, controversy remains regarding the effect of spatial confinement on the functionality of the oxide material.
Our group has developed a novel vapor diffusion sol-gel approach to the synthesis of perovskite oxide nanocrystals under ultrabenign conditions (atmospheric pressure, low temperature, and near neutral pH). Gas-liquid rather than liquid-liquid hydrolysis and the compositional flexibility of the method afford the preparation of complex perovskite sub-30 nm nanocrystals of arbitrary and well-defined stoichiometry. A comprehensive structural picture of perovskite oxide nanocrystals was achieved using a series of instrumental techniques that probe the atomic structure on different length and time scales. Specifically, a dual space approach to the structural analysis of nanocrystals that combines Rietveld and pair distribution function analysis of X-ray scattering, as well as X-ray absorption spectroscopy data was employed. This set of techniques allowed for a fundamental understanding of the effect of spatial confinement and chemical substitution on dipole-dipole cooperative interactions that are the structural basis for ferroelectricity.

III-V quantum dots (QDs) are promising candidates for replacing the more frequently used II-VI and IV-VI QDs in a variety of applications, such as novel display technologies or in-vivo biomedical imaging. In particular, indium based QDs offer an alternative to cadmium or lead containing II-VI and IV-VI QDs. However, III-V QDs exhibit much broader size distributions than those QDs, which makes them unsuitable for many optical applications. Previous experiments have shown that the particle size distribution strongly depends on the conversion rate of the molecular precursor in the process of forming nanocrystals.
We used ab-inito DFT calculations to investigate the reactivity of group-V precursors during the early stages of III-V QD growth. In a systematic study the reaction energies and thermochemistry of molecules with the general structure (R3E)3V (R = H, Me, Et; E = Si, Ge, Sn; V = P, As, Sb) have been calculated. We examined the influence of steric and electronic factors on the formation of the early intermediates to pave the way for a rational design of future QD precursors.
To supplement the calculations we compared our results to the experimentally obtained kinetic data from known group-V precursors. Together, our data begin to provide a rich picture of quantum dot growth at a molecular level, and enable us to test existing theories of particle formation.

Ionic conductor bismuth (III) oxide in solid solution with dysprosium, gadolinium, yttrium and/or tungsten is investigated as a potential electrolyte for Intermediate-Temperature Solid Oxide Fuel Cells (ITSOFCs) designed to operate between 500C and 700C. Focus is placed on co-substitution at the lowest total dopant level required to stabilize the cubic structure in the range of room temperature to 800C. The materials are prepared by a nitration precursor method and characterized using several techniques that include: x-ray diffraction (XRD) to identify phase composition and to determine the extent of solid solution; scanning electron microscopy (SEM) to examine microstructure; and energy dispersive spectroscopy (EDS) employing x-ray compositional dot mapping to confirm chemical homogeneity. Ionic conductivity for both the bulk and grain boundary is measured with electrochemical impedance spectroscopy (EIS), which also serves as a screening tool to determine the suitability of an ion conductor as a fuel cell electrolyte.

Among the mixed metal oxides, perovskite and perovskite-related structure oxides remain prominent for oxide functional materials.
For industrial application of SOFC cathodes materials, numerous requirements such as long term chemical and structural stability at working condition, and mechanical reliability must be satisfied. In this work high-temperature X-ray diffraction has been used to investigate thermal and chemical expansion as well as overall phase stability of various cathode materials: Ba0.5Sr0.5Co0.8Fe0.2O3, La0.3Sr0.7CoO3, La0.6Sr0.4CoO3, La0.6Sr0.4Fe0.8Co0.2O3, and (La0.8Sr0.2)0.95MnO3 as a function of temperature and various working atmospheres (ambient, inert and reducing conditions). In general, stability is controlled by the B-site cations under reduced oxygen pressure. Lattice expansion in the oxygen-deficient perovskites occurs through two mechanisms: thermal expansion and chemical expansion that occurs upon a decrease in oxygen stoichiometry, accompanied by reduction of the B-site cations to maintain the charge neutrality in the solid with increasing temperature and decreasing oxygen partial.LSF is most stable, while LSC and LSCF form oxygen vacancy-ordered phases and then decompose when heated to 1000°C under atmospheres with pO2 as low as 10-5 atm. We generalize the behavior based on the oxygen vacancy content and flexibility in the B-site cation valence.

A ternary compound composed of 0.33(Ba0.70Sr0.30TiO3)+0.33(Ba0.70Ca0.30TiO3)+ 0.33(BaZr0.20Ti0.80O3)-(BST-BCT-BZT) was synthesized by conventional solid-state reaction techniques. In our continuing search for developing new ferroelectric materials, we report stoichiometric compositions of complex perovskite ceramic materials: (BST-BCT-BZT) with diffuse phase transition behavior. The ceramic materials were prepared using high-energy ball milling for 4 hrs at 400 rpm. The milled powders were calcined at 1250C/10 hrs. Ceramic pellets were prepared using hydraulic press and sintered at 1500C/4 hrs. The crystal structure, dielectric properties, ferroelectric and energy storage properties were characterized. XRD studies of the sintered pellets revealed the pure perovskite crystal structure. Well-saturated ferroelectric hysteresis P-E revealed high saturation polarization ~15 C/cm2 at a maximum field 100 kV/cm. High dielectric constant (ε~770), low dielectric loss (tanδ~0.16) with low conductivities are recorded at room temperature. High discharge energy density of 1.246 J/cm3 is recorded at maximum filed. The variation on the phase transition temperature, dielectric constant, and ferroelectric to paraelectric phase transitions and energy storage densities with composition are discussed.

Mixtures of Al and Cu powders were ultrasonically consolidated at different nominal consolidation temperatures of 50 °C to 500 °C under 100 MPa. Full compact densification and metallurgical bonding was achieved in specimens subjected to ultrasonic vibration at 400 °C and 500 °C for 2 seconds or longer. These specimens also exhibited a reaction zone between the aluminum and copper particles where intermetallic phases were formed. Energy Dispersive Spectroscopy (EDS) and X-Ray Diffraction (XRD) identified three layers of intermetallics, Al2Cu, AlCu and Al4Cu9, in the reaction zone. Reference specimens compacted at 500 °C under identical conditions but without ultrasonic vibration were not fully dense nor metallurgically intact and had no reaction zones. Formation of intermetallic phases in the ultrasonically consolidated specimens is an indicator of local melting at the Cu particle interface in the Al matrix, which might occur below the equilibrium melting point of aluminum.

Reactive hybrid bimetallic-thermite composites were fabricated from nanothick Al and Ni flakes and oxide nanoparticles (Fe₂O₃ and CuO) by ultrasonic powder consolidation (UPC). The hybrid reactive composites combine the large heat output of an Al-metal oxide thermite and the lower ignition temperature of an Al-Ni bimetallic composite. Al-Ni-Fe₂O₃ and Al-Ni-CuO composites consolidated at Tle;573 K and uniaxial pressures le;100 MPa had fully dense, uniform composite microstructures with no evidence of reactions among the constituents. Continuous heating caused the hybrid reactive composites to ignite well below the Al-Al3Ni eutectic temperature, confirming that a reaction between the Al and Ni flakes triggers the ignition. Lower ignition temperatures were observed with composites with higher Al contents, i.e., higher Al-Ni interfacial areas, but at the expense of heat output. Hybrid bimetallic-thermite composites may provide heat sources suitable for micro-joining and flexible electronics bonding.

Crystals of a new composition, VOSbOPO₄, have been prepared by hydrothermal and molten salt flux methods. The structure was determined by single-crystal X-ray diffraction. The compound crystallizes in the monoclinic space group P21/n, with lattice parameters a=7.998(5) Å, b=5.709(3) Å, c=11.583(7) Å, and β=93.935(13)°. It is related in structure to vanadyl pyrophosphate (VPO), an important selective oxidation catalyst. TGA and PXRD measurements show a 6% weight gain when heated in air up to 700°C with no gross change in the crystal structure. Analysis of the crystal structure revealed sites where the extra oxygen could reside. The compound shows activity for the oxidation of butadiene to furan, but only after being pre-treated in air at 500°C.

Secondary solid-state transformations of as-synthesized nanoparticles (NPs) are an emerging and powerful method to tailor the NPs composition and morphology. Synthetic work has centered on creating new nanoparticles using these transformations, however, beyond empirical qualitative analysis, few works have addressed the atomic mechanisms for these transformations. In this work we present the atomic structural changes and diffusion processes during the chemical transformation of ε-Co NPs through air oxidation into hollow CoO NPs and then Co₃O₄ NPs.1 During this chemical transformation from ε-Co to CoO, the single-crystal spherical ε-Co NPs convert to polycrystalline hollow CoO NPs due to the nanoscale Kirkendall effect. This morphology remains as the NPs transform to the Co₃O₄ phase upon further heating. The Co₃O₄ NPs can be redispersed in an organic solvent by adding surfactants, thus rendering a method to create solution-processable colloidal, monodisperse Co₃O₄ NPs.
Through a thorough investigation with XRD, EXAFS, TEM, and DFT calculation, we elucidate the atomic structural change and diffusion mechanisms during the oxidation from ε-Co to two phases (CoO and Co₃O₄) of cobalt oxide NPs. Our DFT calculations and experimental results suggest that a two-step diffusion process is responsible for the Kirkendall hollowing of ε-Co into CoO NPs. The first step is O in-diffusion by an indirect exchange-mechanism through interstitial O and vacancies of type I Co sites of the ε-Co phase. This indirect exchange mechanism of O has a lower energy barrier than a vacancy-mediated diffusion of O through type I sites. When the CoO phase is established the Co then diffuses outward faster than the O diffuses inward, resulting in a hollow NP. The lattice orientations during the transformation show preferential orderings after the single crystalline ε-Co NPs are transformed to polycrystalline CoO and Co₃O₄ NPs. Our Co₃O₄ NPs possess a high ratio of {110} surface planes, which are known to have favorable catalytic activity. These insights on the transformation mechanism provide an important step towards understanding the mechanism so that secondary solid-state transformations can be predictively harnessed.
[1] D.-H. Ha, L.M. Moreau, S. Honrao, R.G. Hennig, and R.D. Robinson, J. Phys. Chem. C. (Accepted, DOI: 10.1021/jp402939e)

The lattice symmetry of crystalline materials is one of the key factors that governs their properties. However the role of symmetry in the chemical transformation of nanoparticles is not well-understood. Here, we demonstrate interface formation through cation exchange in nanoparticles driven by the symmetry of their crystal structures. Specifically, we perform a cation exchange reaction on monoclinic copper sulfide nanoparticles, transforming them to wurtzite zinc sulfide. Due to the low symmetry of the starting monoclinic crystal structure, interfaces form between the copper sulfide phase and zinc sulfide phase symmetrically from two sides of the nanoparticles. By controlling the reaction time, the 2-dimensional copper sulfide layer in the center can be tuned to widths between 1 nm and 10 nm confined between two regions of zinc sulfide. Upon full conversion the zinc sulfide nanoparticles preserve the original shape and size of the starting copper sulfide nanoparticles. Both interface formation and confinement are achievable with other nanoparticle morphologies such as hexagonal bifrustums with the same monoclinic symmetry. However, copper sulfide nanoparticles with a similar morphology but a different phase (hexagonal symmetry) do not develop interfaces during the cation exchange to zinc sulfide. This is likely due to the higher-symmetry phase, which leads to near-isotropic growth of the zinc phase. Knowledge about this interface formation through chemical transformation controlled by the symmetry of their crystal structure may provide a new approach to create a heterostructure in nanomaterials.

BaYFeO₄ crystallizes in an orthorhombic Pnma structure, which is isostructural to Ba₂Y₂CuPtO₈¹, and consists of two unique Fe sites that are alternately corner-shared [FeO₅]^7- square pyramids and [FeO₆]^9- octahedra, forming into [Fe₄O₁₈]^24- rings.² There are two discernable antiferromagnetic transitions at 36 and 48 K and the heat capacity measurements reveal no magnetic phase transitions. Interestingly enough, there is an upturn in the magnetic susceptibility measurements up to 400 K, suggesting low dimensional magnetic behavior and the possibility of a maximum above 400 K. In an effort to understand the observed magnetic behavior in BaYFeO₄, we have performed variable-temperature neutron powder diffraction measurements as well as high-temperature magnetic susceptibility. Indeed, neutron diffraction measurements confirmed the two magnetic transitions observed at 36 and 48 K. Below 48 K, the magnetic structure was determined with a propagation vector, k=0,0,1/3, whereas the structure becomes incommensurate (k=0,0,~0.35) at lower temperatures. Furthermore, the high-temperature magnetic susceptibility measurements revealed a maximum at ~ 510 K. The magnetic properties and structure of a novel iron-based compound, BaYFeO₄, will be presented.
1. Swinnea, J. S. and Steinfink, H. Acta Cryst.1987, C43, 2436.
2. Wrobel, F.; Kemei, M. C.; Derakhshan, S. Inorg. Chem.2013, 52, 2671.

Co₁₀Ge₃O₁₆ crystallizes in an intergrowth structure featuring alternating layers of spinel and rock salt. Variable-temperature powder synchrotron X-ray and neutron diffraction, magnetometry, and heat capacity experiments reveal a magnetostructural transition at T_N = 203 K. This rhombohedral-to-monoclinic transition involves a slight elongation of the CoO₆ octahedra along the apical axis. Below T_N, the application of a large magnetic field causes a reorientation of the Co²⁺ Ising spins. This metamagnetic transition is first-order as evidenced by a latent heat observed in temperature-dependent measurements. This transition is initially seen at T = 180 K as a broad upturn in the M-H near H_C = 3.9 T. The upturn sharpens into a kink at T = 120 K and a "butterfly" shape emerges, with the transition causing hysteresis at high fields while linear and reversible behavior persists at low fields. H_C decreases as temperature is lowered and the loops at positive and negative fields merge beneath T = 20 K. The antiferromagnetism is described by k_M = (00½) and below T = 20 K a small uncompensated component with k_M = (000) spontaneously emerges. Despite the Curie-Weiss analysis and ionic radius indicating the Co²⁺ is in its high-spin state, the low-temperature M-H trends toward saturation at M_S = 1.0 mu;_B/Co. We conclude that the field-induced state is a ferrimagnet, rather than a S = 1/2 ferromagnet. The unusual H-T phase diagram is discussed with reference to other metamagnets and Co(II) systems.

Barium zirconium calcium titanate (BZCT: [Ba0.91Ca0.09][Zr0.14Ti0.86]O) has been shown to have increased dielectric properties and polarization values compared to raw barium titanate making it favorable for energy storage applications. However, as a sintered ceramic, it still maintains the fatal flaw of low breakdown strength due to high porosity and high-energy grain boundaries. In order to reduce these flaws, ceramics can be composited with low melting temperature glass that is able to diffuse more easily at low temperatures allowing for a less porous material that consequently will have a higher breakdown strength. After the sintering process, an increase in temperature can crystallize the glass into a ferroelectric, ceramic phase similar to that of the BZCT. This allows for a low porosity, high dielectric material sintered at relatively low temperatures (<1000° C). The energy storage of a multilayer capacitor can be further increased by reducing the thickness of the dielectric layers. Herein, we examine the thickness dependence on BZCT-BZCT based alkali-free glass composite films. Films were printed using a tape casting method to a thickness of 50 microns. In order to vary the thickness (50-200 microns), these cast films were stacked, pressed, and then heat-treated to burn out the tape binder. The films were then sintered onto Ag:Pt:Pd electrodes. A Ag top electrode was painted on forming a parallel plate capacitor. Hysteresis loops and temperature dependent dielectric properties were measured resulting in a curie temperature of 120 C and room temperature dielectric constant of 130. Polarization loops were measured using Radiant's Precision Ferroelectric Tester. The energy was calculated based of the integral of the PE loops resulting in 0.8 J/cm3.

Preform-to-fiber drawing is a well-established process in as far as silica fibers are concerned, and has been applied recently to other glassy materials system with the drawing of in-fiber devices for applications ranging from medical to sensing. However, materials seen in those fibers are confined to those who have proper viscosity at drawing temperature. A lot of chemicals with good electrical or opto-electrical properties could not be used in fiber devices just because of their unmatched melting point or thermal expansion. Here we discuss inducing chemical reaction during fiber drawing to synthesize chemicals inside fiber devices. The product synthesized not necessarily has to have desired thermal properties as required before. Two examples include synthesizing ZnSe when drawing with polymer cladding at ~200 oC, and synthesizing Si from Al with quartz cladding. In-fiber compound is analyzed by a multiplicity of materials characterization tools, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman microscopy, energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD), all resulting in unambiguous identification of ZnSe as the compound produced from the reactive fiber draw. An in-fiber ZnSe/Se heterojunction is designed and fabricated to demonstrate the prospect of ZnSe-based fiber optoelectronic devices. Also, a nucleation process is observed in Si in situ synthesis with the help of SEM and EDX analysis. The ability to synthesize new chemicals during fiber drawing and to characterize them at the atomic-level extends the architecture and materials selection compatible with multimaterial fiber drawing, thus paving the way towards more complex and sophisticated functionality.

Ion exchange has emerged as an effective technique in synthesizing ionic nanoparticles (NPs) with unique geometries and structures that are not easily achieved by conventional synthetic methods. Compared to the well-developed cation exchange processes, the reactivity of the few reported anion exchange reactions are considerably lower, and temperatures higher than 200 C or reaction times longer than 6 hours is required. The low reactivity of the anion exchange reactions may be due to the reactivity of the reagents used in the syntheses. In this work we find that ammonium sulfide is an effective precursor for low-temperature anion exchange reactions. Ammonium Sulfide exhibits high reactivity as a sulfide reagent in the anion exchange reaction transforming hollow CoO into cobalt sulfide NPs. The overall NP morphology (spherical and hollow) is retained in the transformation. The faster diffusion of Co2+ and O2minus; than the incoming S2minus; during the anion exchange causes a significant expansion of the NP voids. This low temperature (70 C) anion exchange reaction produces amorphous cobalt sulfide NPs with Co : S ratio of ca. 3 : 4, which are converted into crystalline NPs with a major phase of cubic Co3S4 by annealing at high temperature in an organic solution. The use of this low-temperature precursor to facilitate anion exchange in NPs should enable new avenues for solid-state chemical tailoring of NPs.

Multicomponent materials constructed from heterogeneous building blocks can offer functionality not accessible in single-phase homogeneous materials. Besides the linear combination of their individual properties, these composites can exhibit reconstructions at the mesoscale that ultimately govern the macroscale properties. Here, we present new synthetic approaches to link well-defined nanocrystals to inorganic glasses and explore their structure-properties relationships. We found enhanced ionic conductivity in Ag₂S-in-GeS₂ nanocrystal-in-glass electrodes [1] and, in another example, enhanced optical contrast when linking electrochromic niobium oxide to embedded tin-doped indium oxide nanocrystals [2]. Our flexible synthetic approach can offer new opportunities to employ mesoscale structure, in tandem with composition, to develop functional materials.
[1] Wang, R. Y., Tangirala, R., Raoux, S., Jordan-Sweet, J. L. & Milliron, D. J. Adv. Mater. 24, 99-103, (2012).
[2] A. Llordes, G. Garcia, J. Gazquez, D.J. Milliron. Nature, in press.

As a promising candidate for low-cost high-temperature shape memory actuator applications, NiTiHf alloys have been the subject of recent studies due to the possibility of adjusting their transformation temperatures by controlling Hf content. The introduction of aluminum to this system provides the potential to form nanoscale Ni2TiAl Heusler precipitates that can strengthen these alloys. The current investigation examines the effect of aluminum addition on the thermal, microstructural, and mechanical behaviors of Ni50Ti30-xHf20Alx (x = 0, 1, 2, 3, 4, 5) alloys through differential scanning calorimetry, X-ray diffraction, optical microscopy, transmission electron microscopy (TEM), atom probe tomography (APT), and compression testing. An in-depth TEM/APT analysis on the successful demonstration of Heusler precipitation in these quaternary alloys will be presented.

The lattice dilation that accompanies reduction of nonstoichiometric oxides is known as chemical expansion. In materials that readily change stoichiometry under varying operating conditions, such as mixed ionic and electronic conductors used as solid oxide fuel cell electrodes, the stresses accompanying expansion can be large enough to lead to mechanical failure and shortened device lifetimes. Factors controlling chemical expansion in perovskite-structured oxides are poorly understood but need to be elucidated in order to lower chemical expansion and improve device durability.
In this work, the role of charge localization in controlling chemical expansion was explored for the first time by computational and experimental approaches. During reduction, the expansion of cations that lower their valence state outweighs the small contraction around the oxygen vacancies that form. Computational predictions using density functional theory showed that delocalizing charge on these cations should lower the chemical expansion coefficient [1]. Experimentally the role of charge localization was studied in the (La,Sr)(Ga,Ni)O_3-δ system, where increasing the Ni content increases the extent of charge delocalization, as demonstrated previously by electrical conductivity measurements [2]. The resulting chemical expansion coefficients were studied macroscopically by in situ dilatometry and thermogravimetric analysis in N₂/ O₂ mixtures and temperatures in the range 600-900°C. These results were compared to a microscopic analysis of expansion by in situ X-ray diffraction measurements over the same temperature and oxygen partial pressure range. For an increase in Ni concentration from 0.1 to 0.5 per formula unit, a decrease in the chemical expansion coefficient of ~13% was observed, in agreement with the theoretical prediction of decreasing chemical expansion coefficient with increasing charge delocalization.
[1] D. Marrocchelli, S. R. Bishop, H. L. Tuller, G. W. Watson, and B. Yildiz, Physical Chemistry Chemical Physics, 14, 12070-12074 (2012).
[2] N. J. Long, F.&’ Lecarpentier, and H. L. Tuller, Journal of Electroceramics, 3 (4), 399-407 (1999).

Metal-Organic Frameworks (MOFs) are especially promising materials for clean energy storage applications, due to their inherent porosity, large surface area and gas storage capacity, tunable nature of ligand geometry and pore size, and convenient functionalization by pre- or post-synthetic modifications. In the past, the MOF synthesis typically involves complicated synthesis of ligands and try-and-error method of MOF constructions. In this work, we have proposed a novel symmetry-adapted approach of constructing ultraporous MOFs. By following this approach, a series of highly porous MOFs were constructed from synthetically-accessible and commercially-affordable ligands, with the BET surface area up to ~4000 m2/g and H2 uptake up to 2.66 wt% at 77K and 1 bar. This is one of highest H2 uptake capacities at atmospheric pressure among all MOFs up to date. The cheap starting materials and high gas uptake capacities make them very promising materials for clean energy storage applications. It should be noted that other MOFs that possess a similar or higher H2 uptake typically suffer from high production cost and unguided synthesis of MOF materials. This symmetry-adapted approach has enabled scientists to design multi-component MOFs from the symmetry point of view and will provide useful guidance to the synthesis of future MOFs that are suitable for clean energy storage.

Bismuth is an interesting material because it has the second lowest thermal conductivity (after mercury) and the highest Hall coefficient; also, no other natural metal is more diamagnetic than bismuth. In addition, elemental bismuth is one of a very few substances in which the liquid phase is denser than its solid phase. However, its most interesting property is its ability to be a superconductor in the amorphous state and not in the crystalline state. For this reason it is interesting to study the amorphous bismuth topology theoretically and try to explain the relation of superconductivity to structure. The topology (Radial Distribution Functions) of a 64-atom amorphous bismuth supercell has been obtained by the undermelt-quench process [1] finding a good agreement with the experimental data obtained by Fujime [2] in the 60&’s. The stability is analyzed by calculating the total energy as a function of the supercell volume and finding the minima of the energy. In this manner the predicted density of amorphous and liquid bismuth is obtained.
[1] Ariel A. Valladares, Juan A. Díaz-Celaya, Jonathan Galván-Colín, Luis M. Mejía-Mendoza, José A. Reyes-Retana, Renela M. Valladares, Alexander Valladares, Fernando Alvarez-Ramírez, Dongdong Qu and Jun Shen, Materials, 4, 716-781, (2011).
[2] S. Fujime, Japan Journal of Applied Physics, 5, 764, 1966.

Counterintuitive though it may be, the absence of the redox-active transition metal cation (Mⁿ⁺) in mixed ion/electron-conducting metal oxides that undergo cation-insertion reactions, such as oxides of manganese [1], vanadium [2], and iron [3], can increase, not decrease, the capacity of the defective material to insert lithium and other cations and thereby increase the quantity of energy stored. As cation-insertion transition metal oxides comprise a key—and long-studied—class of materials for electrochemical energy storage (EES) in devices ranging from Li-ion batteries to electrochemical capacitors, getting something (higher specific capacity and energy density) for nothing (removing Mⁿ⁺ from a structural unit) offers a promising and still under-exploited phenomenon in EES [4]. As highlighted with examples from past and ongoing work, three protocols will be described to incorporate cation vacancies into transition metal oxides to improve performance in both aqueous and nonaqueous energy storage: (1) inducing point defects in conventional oxides using appropriate atmospheric conditions with a driving force such as temperature; (2) substitutional doping of a highly oxidized cation into a metal-oxide framework; and (3) expressing insertion oxides in morphologies with high surface areas, such as aerogels, that increase the fraction of surface sites that favor formation of cation vacancies.
[1] P. Ruetschi, R. Giovanoli, Cation vacancies in MnO₂ and their influence on electrochemical reactivity. J. Electrochem. Soc.135 (1988) 2663.
[2] K. E. Swider-Lyons, C. T. Love, D. R. Rolison, Improved lithium capacity of defective V₂O₅ materials. Solid State Ionics152-153 (2002) 99.
[3] B. P. Hahn, J. W. Long, A. N. Mansour, K. A. Pettigrew, M. S. Osofsky, D. R. Rolison, Electrochemical Li-ion storage in defect spinel iron oxides: The critical role of cation vacancies. Energy Environ. Sci.4 (2011) 1495.
[4] B. P. Hahn, J. W. Long, D. R. Rolison, Something from nothing: Enhancing electrochemical charge storage with cation vacancies. Acc. Chem. Res.46 (2013) 1181.

Lithium-ion batteries are now widely adopted for powering small, portable devices and, on a larger scale, hybrid-electric- and all-electric vehicles. Demands by the consumer electronics, medical, defense and transportation industries for more and more energy in a relatively small confined space are stretching the limits to which energy can be stored and released safely.
This presentation will discuss the results of research strategies at Argonne National Laboratory to design electrode materials that may provide more capacity and energy than conventional lithium-ion battery products with carbon anodes and lithium-metal-oxide or lithium-metal- phosphate cathodes. Particular attention will be given to advances in the design and characterization of high capacity, composite lithium-metal-oxide cathode structures for lithium-ion cells, as well as dual-functioning electrocatalytic metal oxide materials for lithium-oxygen cells.
Acknowledgments
This work was funded by the U.S. Department of Energy under Contract No. DE-AC02-06CH11357. The high capacity, composite lithium-metal-oxide electrode research was supported by the Office of Vehicle Technologies, whereas the lithium-oxygen cell research was supported, in part, by the Center for Electrical Energy Storage, an Energy Frontier Research Center funded by the Office of Science, Office of Basic Energy Sciences.

Maximizing the electrical energy stored in, and drawing high power from Li-ion batteries requires preparative methods that generate high purity nanomaterials. Although low temperature synthesis methods known to generate nanoscale materials have been adapted for promising candidates for Li-ion battery technology, their electrochemical performance is often plagued by point defects, particle aggregation, and impurity phases—all of which can be minimized if one has a thorough understanding of and appreciation for inorganic reaction chemistry. I will highlight three classes of materials currently under investigation in my laboratory: 1) manganese-based spinel nanoparticles synthesized by hydrothermal methods; 2) lithium titanate spinel nanocrystals synthesized by a templated sol-gel method; 3) bronze-phase titania microflowers synthesized by hydrothermal synthesis followed by aqueous work-up. I will provide details of the synthetic chemistry used to generate these materials along with guidelines that can be applied to many solid oxides. In addition, I will show that electrodes composed of nanomaterials show similar energy density and stability compared to those composed of their micron-sized congeners. Most important, the rate capability is superior because of the small particle sizes we obtain from our synthesis methods.

The synthesis and identification of new compounds that can lead to enhancements in existing technologies, or serve as the basis of revolutionary new technologies, is essential for developing new and improved technologies. The Zintl concept is used to distinguish a class of solid state compounds whose structure can be understood according to simple electron counting rules. Zintl compounds can be described by a combination of ionic and covalent bonding, composed of electropositive cations which donate electrons to the more electronegative components that utilize the electrons to form various bonding motifs. These simple bonding ideas provided the framework for the exploration of the frontiers of this area. Thermoelectric devices can recycle waste heat and therefore enhance energy use ratio. They can also generate cool air without discharge of green house air. Zintl phases have the potential to serve as high efficiency thermoelectric materials in thermoelectric devices because of their complex structures and ability to finely tune the transport properties. My group has focused on Zintl compounds for their structural, chemical, and electronic properties as well as for their synthetic utility. In this talk, I will present our current directions in research on Zintl phases and provide a summary of new compounds with promising properties.

The solid-state chemistry of the cathodes used for lithium-ion batteries determines whether a battery is safe and long lived or unravels into an unstable liability. We are using both high-energy X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) to probe how atomistic changes in the particle bulk and surface determine the battery stability. Lithium copper oxide, Li₂CuO₂, was studied for its promise of high capacity through the access of charge states from Cu¹⁺ to Cu³⁺ (C. Love, et al., J. Solid State Chem. 184 (2011) 2412). The XRD of the Li₂CuO₂ at various states of charge was resolved with pair distribution function (PDF) analysis, and showed that the Cu charge is highly irreversible. During cycling, the results indicate that charging the material results in O₂ loss rather than Cu³⁺ reduction. The orthorhombic Immm Li₂CuO₂ structure breaks down to CuO, blocking Li⁺ uptake and capacity.
Lithium cobalt oxide, LiCoO₂, the more standard cathode material in lithium-ion batteries was also investigated. Micron-scale LiCoO₂ has excellent capacity retention with cycling, so we studied it as a nanomaterial to accentuate its instabilities and particle surface effects. In this case, we probed the battery in situ using XAS, and then analyzed the results through the spectrum difference method, Δµ (Patridge, et al., J. Solid State Chem., 203 (2013) 134). Again, the occurrence of a destabilizing structural change occurs, in this case a site exchange between the metal cations and Li⁺. By the difference methodology, we deduce that the Co³⁺-Li⁺ place exchange is predominantly at the particle surface of the planar, R3m LiCoO₂ material, thus explaining why micron-scale LiCoO₂ is more stable. These fundamental insights into the solid-state chemistry of two oxide battery materials can be used toward the design of more robust materials.

This discussion will address approaches towards sodium ion batteries with the use of fluorinated materials. Three concerns of energy use include i) energy storage, ii) expense of lithium sources, and iii) the operating voltage of a battery. As renewable energy sources, such as solar, wind, hydropower, are increasing, issue (i) must be addressed to store excess energy for later use. This has been approached with the use of Li+ ion batteries. Issue (ii) compounds issue (i) as large Li+ batteries may be prohibitively expensive on a large scale. Sodium ion batteries are under investigation as a low-cost alternative, but issue (iii) complicates this as sodium ion batteries have lower voltages (-0.2 to -0.5 V) as compared to lithium analogs owing to thermodynamic effects.
To address these issues, we present structural and electrochemical analyses of a new double-wolframite trimetallic compound: AgNa(VO2F2)2 or SSVOF; SSVOF is a fully ordered material and displays attractive electrochemical characteristics. The compound contains trioxo vanadium fluoride octahedra which form one dimensional chains that are characteristic of wolframite (NaWO4). To approach issues (i) - (iii) we evaluated SSVOF within Li+ and Na+ batteries.

The design of efficient and cost effective catalysts is fundamental for many electrochemical energy conversion and storage reactions such as Oxygen Evolution Reaction (OER) or Oxygen Reduction Reaction (ORR). However, only the understanding of materials structure - properties relationship could provide an accurate descriptor to design effective catalysts and achieve high activity. Perovskite-related oxides AMO3-δ are the perfect playground for chemists to tailor the metal-oxygen bond and to shape oxides with the required physical properties as their electronic structure can be easily tuned. As shown by Suntivich et al., the OER activity of Perovskite in alkaline solution can be predicted by the filling of transition metal eg orbital electrons [1]. Indeed, the energy of an adsorb oxygen on the surface of transition metal oxides is greatly influenced by the extent the σ* antibonding orbital, coming from the hybridization of the transition metal eg and the oxygen 2p orbitals, is filled.
Nevertheless, the ability to synthesis new inorganic catalysts is highly restricted by the use of such activity descriptor which cannot be easily computed. Following the success of DFT calculated d-band center for metal surfaces [2], we herein proposed a new descriptor for the OER activity of transition metal oxides which can be easily computed: the O p-band center. The OER activity of cobalt-based perovskites was measured and their O p-band center calculated by DFT. As the O p-band center is getting closer to the Fermi level, the charge transfer between the adsorbate and the catalyst is enhanced and the OER activity increases until to reach a value (~ -1.8 eV) above which the oxide is not stable anymore in alkaline solution under OER conditions. These calculations were supported by X-ray adsorption (XAS) measurements at the O K-edge and the stability of transition metal oxides was analyzed by high resolution transmission electron microscopy (HRTEM).
[1] - J. Suntivich, K.J. May, H.A. Gasteiger, J.B. Goodenough and Y. Shao-Horn, Science, 2011, 334, 1383
[2] - B. Hammer, J. K. Norskov, Advanced Catalysis, 2000, 45, 71.

Ternary arsenides that exhibit itinerant magnetism represent significant interest in the light of the discovery of FeAs-based superconductors. The Co-containing analogues of these superconductors also have been extensively investigated, but only in the A-Co-As systems, where A = alkali or alkali-earth metal. In contrast, studies in the R-Co-As systems (R = rare-earth) are extremely scarce. Our attempt at repeating the only reported synthesis of RCo2As2 from Sn flux demonstrated the failure of this method to produce phase-pure materials or representative single crystals. In the search of an alternative synthetic approach, we turned to Bi flux, which allowed the successful preparation of LaCo2As2, as recently reported by our group. Encouraged by such development, we employed this synthetic methodology for an exploration of the other ternary R-Co-As systems. This paper will report the preparation of a broad range of ternary rare-earth cobalt arsenides from Bi flux, as well as their crystal structures and magnetic properties.

Ferromagnetic semiconductors have been of great interest over the last several decades because of their potential applications in novel technologies such as the spintronics . However, for spintronic applications, further research is needed to: (1) overcome the conductance mismatches between the semiconductor and metal used to inject spin into the semiconductor, (2) increase the Curie temperature, and (3) achieve controllable correlation between charge and spin . In order to cooperatively manipulate the ferromagnetism and semiconductivity, we have designed a new approach based on the chemistry of M(IV,V)2VI4 compounds (M = transition metal). This approach is promising due to flexible control over the magnetism and the crystal symmetry of the resulting materials. Here, we discuss the chemical manipulation of the magnetic and electronic properties of FeSb2Se4, a narrow gap semiconductor exhibiting ferromagnetism up to 300K . FeSb2Se4 showed a cooperative structural distortion affecting both the magnetism and electronic properties. To investigate these electronic and magnetic transitions, we performed Sn substitution at Sb sites in the structure of FeSb2-xSnxSe4 in order to probe the effect of Sb electron lone-pair on the structural distortion and the magnetic and electronic properties. We found that, the electronic transition (SI) temperature gradually decreases upon Sn to Sb substitution from 180K to 51K. This suggests decreasing effect of the lone pair due to Sn substitution at Sb sites. For x = 0.15, the electronic transition observed at 130K is reversed at ~60K indicating that the stereo-activity of the Sb lone pair maybe vanishing at very low temperatures. Regardless of the temperature, the magnetic susceptibility monotonically increases with Sn concentration reaching peak values at x = 0.2 and decreases with further increase in Sn concentration. The coercivity and the saturation magnetization were also found to be strongly dependent on the Sn concentration. We attempt to correlate the observed alteration of the magnetism and conductivity in FeSb2-xSnxSe4 to the variation of charge carrier concentration and mobility upon Sn2+ substitution at Sb3+ sites.

Density functional theory was used to identify chemical influences on magnetic ordering and metal-atom site preference of stoichiometric CrMnAs, one of a class of 3d-metal arsenides that exhibit cooperative itinerant magnetism. CrMnAs adopts a tetragonal structure with two inequivalent metal sites: M(I), which is tetrahedrally coordinate by As, and M(II), which is square pyramidally coordinate by As. CrMnAs thus presents a “coloring problem,” the question of how the two types of metal atoms are distributed between the two types of metal atom sites. Previous diffraction studies have determined CrMnAs to be antiferromagnetic with a magnetic unit cell that is doubled along the tetragonal c-axis, and with the M(I) site primarily occupied by Cr. The electronic structures of three possible metal-atom colorings and 15 distinct magnetic ordering patterns of CrMnAs were examined using tight-binding, linear muffin-tin orbital methods, and their total energies were evaluated using VASP, which included the generalized gradient approximation, both with and without an empirical site-repulsion parameter (+U). Although the two overall lowest energy configurations had Mn at the M(I) site and different magnetic orderings than has been reported, four antiferromagnetic structures with Cr at the M(I) site were the next lowest energy configurations. The computational results raise the possibility that the observed magnetic and chemical ordering in CrMnAs could be significantly influenced by configurational entropy, rather than reflecting the true electronic ground state. A Boltzmann distribution of calculated structures supports the presence of an entropy-driven mix of magnetic orderings and colorings at reported annealing temperatures. This work was supported by the National Science Foundation, Materials World Network (NSF DMR 12-09135).

Cubic indium oxide (In₂O₃) is not only known as a transparent conductor (if doped with tin; ITO) but also as a material for resistive gas sensors, since, like many other n-type semiconducting metal oxides, its conductivity changes upon interaction with various gases. At low temperature (< 150 °C) In₂O₃ is particularly sensitive to oxidizing gases such as ozone or nitric oxides in very low concentrations (ppb), but rather insensitive to reducing gases. This makes In₂O₃ a candidate for low-temperature (and low-power) sensing of oxidizing gases, even though the underlying mechanism for this behavior is not entirely understood so far. To operate the sensor at low temperature with sufficiently fast response optical activation has been shown to be a versatile means. In₂O₃ is known to exhibit strong (persistent) photoconductivity when illuminated with UV light and a related fast reaction and regeneration of the sensor signal upon gas exposure; this phenomenon is not exhaustively understood, either, since it is not explainable by the standard models for gas sensing focused on surface effects and the formation of depletion layers (such as the ionosorption mechanism).
Nanoporous In₂O₃ was chemically synthesized by a structure-replication (nanocasting) technique. In short, the synthesis comprises utilization of mesoporous silica (SiO₂) as a structural matrix; In₂O₃ is created in the pores of the matrix, followed by selective etching of the silica phase. We present a model of UV light-activated gas-sensing properties based on photoreduction of In₂O₃, emphasizing oxygen diffusion into and out of the In₂O₃ lattice as a rate-limiting step. Oxygen vacancies rather than, e.g., hydrogen impurities are regarded as responsible for the high carrier concentration; hence, generation and annihilation of these vacancies explain the observed persistent photoconductivity. Experimental evidence is based on conductivity measurements under controlled atmosphere (synthetic air, pure N₂). The energy level of the donor state related to the oxygen vacancies was determined to ca. 180 meV by in-situ Fourier transform infrared (FTIR) spectroscopy. Well-ordered nanoporous In₂O₃ was used as the model system because of its unique structure; the behavior of this material is dominated by the proposed effects. The resulting nanostructured In₂O₃ replica exhibits structural dimensions below 10 nm which means that oxygen diffusion effects in the crystal lattice are dominant, contrary to bulk-phase In₂O₃ (although our model applies to both the nanoscopic and the bulk phase). The results of the study also offer new insight into the resistive gas-sensing mechanism of In₂O₃.

Low-dimensional materials are promising candidates for thermoelectric applications owing to the enhancement of the Seebeck coefficient that may occur as a result of spatial confinement of the charge carriers. As part of our on-going investigations of the structural and physical properties of low-dimensional chalcogenides, we have begun to explore the effects of chemical substitution in Cr₂Ge₂Te₆. The parent structure consists of hexagonally close packed Te^2- ions, with Cr³⁺ ions and (Ge₂)⁴⁺ pairs occupying the octahedral sites between alternate pairs of close-packed layers in an ordered fashion. In an effort to manipulate the electrical transport properties of this phase, we have investigated the effects of progressive substitution with indium through preparation of the series, Cr_2-xIn_xGe₂Te₆ (0 le; x le; 2). Powder neutron diffraction reveals that the three-layer structure of the end-member phase, Cr₂Ge₂Te₆ (R-3) is retained only until x=0.2, above which a change in stacking sequence of the metal-telluride slabs occurs, leading to a two-layer repeat along [001] to x values of 1.2. At higher levels of indium incorporation (x>1.4), superlattice reflections become weak and diffuse, indicating that the two-dimensional order begins to break down. Low-temperature powder neutron diffraction data also indicate that increasing levels of indium substitution suppress long-range magnetic order: no magnetic scattering being observed for the sample with x=1.0. Substitution also induces marked changes in transport properties and leads to a high Seebeck coefficient in the end-member phase In₂Ge₂Te₆.

We have recently investigated the electronic and magnetic properties of Mn2+ oxypnictides LaMnAsO and NdMnAsO. Neutron diffraction results show that both LaMnAsO and NdMnAsO are antiferromagnetic with transition temperatures of 370 K. LnMnAsO (Ln = Nd, La) are both semiconducting and a sizeable negative magnetoresistance (MR) is observed at room temperature. The series NdMnAsO1-xFx (x = 0 - 0.085) has been synthesised; NdMnAsO1-xFx shows colossal negative magnetoresistance at low temperature (MR7T (3 K)) = -95%. We will present variable field neutron diffraction results which show that there is a phase transition from antiferromagnetic order of the Mn2+ and Nd3+ spins in zero field to paramagnetism at higher fields. The MR is related to the magnitude of the antiferromagnetically ordered Mn2+ moment.

Low-dimensional spin systems have gained much attention in solid state physics. Such systems could have a ground state with no long-range magnetic order, offering the possibility of a quantum spin-liquid phase. The quantum fluctuations are particularly strong in systems with reduced dimensionality and a low spin value; and magnetic frustration can further enhance the fluctuations. Among various low-dimensional spin systems, the S = 1/2 Heisenberg frustrated square lattice model is especially interesting due to its relevance to high-T_c superconducting cuprates, whose undoped parent materials are S = 1/2 square-lattice antiferromagnets.
In this work we characterize Sr₂CuWO₆ and Sr₂CuMoO₆ compounds with both experimental and computational methods. These compounds have been found to be quasi-two-dimensional S = 1/2 magnetic systems with a square lattice, due to orbital ordering in the Jahn-Teller active Cu^II ion [3]. In addition, they appear have frustrated nearest and next-nearest neighbor magnetic interactions, and the frustration is higher in Sr₂CuMoO₆ than in Sr₂CuWO₆. These compounds show low-dimensional, short-range magnetic properties, with no clear indication of long-range order in magnetic susceptibility. The magnetic exchange interactions were determined by DFT electron-structure calculations. A relatively large on-site electron-electron correlation in copper is found, which strongly affects the calculated exchange interaction parameters. DFT-U calculations were performed in order to take this correlation into account, and the value of U was determined from O K-edge XANES data.
[3] S. Vasala, J.-G. Cheng. H. Yamauchi, J. B. Goodenough, M. Karppinen, Chem. Mater.24 (2012) 2764.

Relatively high levels of oxygen deficiency can exist in certain oxide materials with both the perovskite and fluorite structures. Among the perovskites, phases such as AAprime;BBprime;O5 are known with a 16.7% vacancy concentration on the O-site. Often, the vacancies order resulting in for example the orthorhombic brownmillerite structure but cases exist in which the vacancies appear to be random with classic Pm-3m symmetry. The local structures of two such perovskites, Sr2FeMnO5 and Sr2Fe1.5Cr.5O5 are studied by
neutron diffraction and analysis of the pair-wise distribution function(PDF). While the average structures are essentially the same, the local structures are quite different which may provide a basis to understand the very different magnetic properties - Sr2Fe1.5Cr.5O5 shows long range antiferromagnetic order below 565K, while Sr2FeMnO5 is a super paramagnet below 50K. Considering the fluorites, certain rare earth tantalates and niobates show oxygen vacancy order/disorder between the ordered, orthorhombic weberite structure and a highly deficient, 12.5% vacancy concentration, Fm-3m form as a function of rare earth (RE) radius.The series RE3TaO7 shows this transition between RE = Ho and Er.[1] These materials have been evaluated recently as catalysts for water splitting.[2] Catalytic efficiency is reported to be drastically reduced in the cubic relative to the orthorhombic structure. The local structure of cubic Yb3TaO7 is studied by
neutron diffraction and analysis of the PDF indicates that it resembles very strongly the ordered weberite out to at least a length scale of 3 nm, about an order of magnitude larger than the molecular length scale at which the catalytic reactions likely occur.
[1] M. Wakeshima et al, J. Phys. Cond. Matter16(2004)4103.
[2] R. Abe et al. J.Phys. Chem.B 108(2004)811.

The thermal expansion characteristics, and the principles underpinning them, of some metal fluorides and oxyfluorides that are structural relatives of rhenium trioxide will be discussed. Their properties can be tailored by solid solution formation, the introduction of anion disorder through oxyfluoride formation, the preparation of slab (2D) solids rather than 3D frameworks, and cation ordering in mixed cation systems. As their properties are in many cases very sensitive to changes in pressure, this will also be discussed.
Close to zero thermal expansion provides both dimensional stability and good thermal shock resistance. Negative thermal expansion can be used to compensate for the positive thermal expansion of other materials. As fluorides and oxyfluorides typically have better infrared transparency than oxides, low thermal expansion fluorides and oxyfluorides have potential for application in IR optics.

Synthesis of porous inorganic metal oxide materials relies on solid state chemistry methods such as precipitation, hydrothermal alteration, high temperature mixing, solvent free methods, sol gel, pulsed laser deposition, and other methods. We will discuss various methods of preparation of such materials and resultant physical and chemical properties. Some properties that can be optimized include composition, structure, morphology, electronic properties, optical properties, porosity, surface area, mechanical properties, surface functionalities, and other properties. Some particular chemical properties of interest include adsorption and catalytic activity. Most of this work concerns small molecules like CO, carbon dioxide, hydrogen and small hydrocarbons. The role of solid state inorganic chemistry in the deign of such materials will be the focus of this presentation.

Double perovskites with stoichiometry A2MM&’O6 where M is a 3d transition metal ion (Cr. Fe, Co, Ni) and M&’ is a 5d transition metal ion (Os, Re, W) are a fascinating class of compounds whose properties can vary dramatically depending on the filling and relative energy levels of the d-orbitals on the 3d and 5d ions. The magnetism can vary from double exchange ferrimagnetism to complex antiferromagnetic structures. In this talk I will discuss studies of new double perovskites in bulk form as well as growth and characterization of epitaxial thin films with a focus on the magnetic properties of these compounds. Computational and theoretical modeling results will be used in combination with experimental data to understand the how the properties change in response to changes in chemical composition and crystal structure.

A systematic study is reported on the range of stability and structure-composition-properties correlation of molybdenum substituted Sr-based 123 compounds synthesized at ambient pressure. A detailed investigation of the structure-composition-properties is carried out for the as-prepared and oxygen annealed pure Mo0.3Cu0.7Sr2RECu2Oy materials. Their crystal structures were characterized by combining X-Ray/neutron powder diffraction and electron diffraction techniques. For the samples with RE = Y and Er, both the as-prepared and oxygen annealed materials show tetragonal symmetry crystallizing in the P4/mmm space group (S. G.). But a tetragonal (Space Group P4/mmm) to orthorhombic (Pmmm) phase transformation has been observed, associated with an oxidation reaction using the combination of neutron powder diffraction and electron diffraction techniques for the Mo0.3Cu0.7Sr2TmCu2Oy sample.
The influence of oxygen annealing in the electronic states for these systems associated with an oxidation reaction from a non-superconducting state to a superconducting one has also been investigated by means of X-ray photoelectron spectroscopy (XPS). these measurements show the predominance of the MoV oxidation state over the MoVI one on both as-synthesized and annealed phases; annealing under flowing oxygen enhances both the MoVI and CuII amounts. On the other hand, the as-prepared Mo0.3Cu0.7Sr2ErCu2Oy material shows the existence of ferromagnetic clusters while the as-prepared Mo0.3Cu0.7Sr2TmCu2Oy material is found to be a re-entrant spin glass (RSG) system.
All the oxygen annealed samples are not magnetic but superconducting (SC) with Tc up to ~85 K (much higher than the high pressure phase CuSr2YCu2O7 : Tc ~60 K).

Many biomaterials combine disparate properties such as exceptional strength, toughness and extensibility with tenability, mutability and a functionality that is unmatched by most man-made materials. This functionality emerges often from simple and abundant constituents that allow the adaption to changing environmental conditions through various feedback loops. Many constituents used in biology are in terms of their properties inferior to current artificial materials because energy as well as material quality and availability are scarce. The excellent performance of many biomaterials originates from a combination of hard and soft building blocks in a multilevel hierarchical structure. A hard inorganic component serves as the reinforcing part and the soft biopolymer allows dissipating energy. The morphology of the mineral blocks and chemical bonding between them provides a physicochemical basis for stiffness and flexibility at multiple scales, leading to an increased robustness against catastrophic materials failure.
Although strong and stiff synthetic composites have long been developed, the microstructure of today&’s most advanced composites has yet to achieve the order and sophisticated hierarchy of hybrid materials built up by living organisms in nature. We have exploited the structure-function relation of nanoscale assembly to synthesize very hard and tough multilayered DOPA polymer/metal oxide nanoparticles (Fe3O4 and TiO2) nanocomposites with a maximum Young&’s modulus of 80 ± 34 GPa (comparable to quartz) and a maximum hardness of 5 ± 3 GPa , respectively, and measured sound velocities of c > 5000m/s. The cross-linked composite films showed high uniformity, strength, flexibility, and good transparency. Thermogravimetric analysis showed that the same films were composed of ~70 wt % of the polymer. These results can be explained from the nanoscale dimensions of the inorganic phase and the close packed arrangement of the nanoparticles. The lamellar nanocomposites contain distinct alternating layers of metal oxide nanoparticles and polymer, strongly cemented together by chelation through infiltration of the polymer between the oxide nanoparticle mesocrystals. Therefore many strong metal polymer bonds have to be broken prior to mechanical failure. The individual nanoparticles are too small to break. In essence, the strong crosslinking between the particles and a multidentate polymer ligand help the matrix resist deformation and make the composite hard and strong. The resulting structure has the characteristics of adhesion and high tensile strength, the hallmark of the original biocomposites in nature.

Cation ordering in transition-metal oxides often drastically modifies the material properties. We here focus on A-and-B-site-ordered quadruple perovskite-structure oxides AA&’₃B₂B&’₂O₁₂, in which transition-metal ions are located at the A&’, B, and B&’ sites in an ordered manner. In the compounds A&’-A&’, A&’-B, A&’-B&’, and B-B&’ interactions compete and play important roles in giving rise to unusual properties. A novel A-and-B-site-ordered quadruple perovskite CaCu₃Fe₂Sb₂O₁₂ with magnetic Fe³⁺ at the B site and nonmagnetic Sb⁵⁺ at the B&’ site was successfully synthesized under a high-pressure and high-temperature condition. The B(Fe³⁺) spin sublattice adapts a tetrahedral framework and the Fe³⁺-Fe³⁺ antiferromagnetic interaction causes a geometrical spin frustration as seen in Ca₂FeSbO₆. With the introduction of Cu²⁺ into the A&’ site, the frustration is relieved by strong antiferromagnetic A&’(Cu²⁺)-B(Fe³⁺) interaction, leading to a ferrimagnetic ordering below 160 K. Another compound is CaCu₃Fe₂Re₂O₁₂ with both magnetic Fe³⁺ and Re⁵⁺ at the B and B&’ sites, respectively, which was also synthesized by a high-pressure technique. When magnetic Re⁵⁺ is introduced in to the B&’ site, strong antiferromagnetic A&’(Cu²⁺)-B&’(Re⁵⁺) interaction overcomes the A&’(Cu²⁺)-B(Fe³⁺) interaction, and as the result, ferrimagnetism with ferromagnetic A&’(Cu²⁺)-B(Fe³⁺) spin arrangement is stabilized below 550 K. More importantly, the compound shows large magnetoresistance by spin-dependent transport at room temperature.