Search

The development of new frameworks for solid electrolytes exhibiting fast Li-ion diffusion is critical for enabling new energy storage technologies. Here, we present a combined experimental and computational investigation into the ionic conductivity of Li6Y(BO3)3, a new class of solid electrolytes with a pseudo-layered structure. Temperature-dependent impedance spectroscopy shows the pristine material exhibits an ionic conductivity of 2.2 × 10−3 S cm−1 around 400 °C, despite the fact that density functional theory calculations point to multiple remarkably low-energy diffusion pathways. Our calculations indicate small energy barriers for lithium interstitials to diffuse along one-dimensional channels oriented in the c-direction, and also for lithium vacancies diffusing within ac planes. This coexistence of diffusion mechanisms indicates that Li6Y(BO3)3 is an extremely versatile host for exploring and understanding mechanisms for lithium-ion conductivity. We also find no evidence for reactivity with moisture in the atmosphere and that the material appears electrochemically stable when in direct contact with metallic lithium. This robust stability, alongside ionic conductivity that can be manipulated through appropriate aliovalent substitution, make Li6Y(BO3)3 an exceptionally promising new class of solid electrolyte. [ABSTRACT FROM AUTHOR]

The intense interest in phase segregation in thermoelectrics as a means to reduce the lattice thermal conductivity and to modify the electronic properties from nanoscale size effects has not been met with a method for separately measuring the properties of each phase assuming a classical mixture. Here, we apply effective medium theory for measurements of the in-line and Hall resistivity of a multiphase composite, in this case Cu1.97Ag0.03Se. The behavior of these properties with magnetic field as analyzed by effective medium theory allows us to separate the conductivity and charge carrier mobility of each phase. This powerful technique can be used to determine the matrix properties in the presence of an unwanted impurity phase, to control each phase in an engineered composite, and to determine the maximum carrier concentration change by a given dopant, making it the first step toward a full optimization of a multiphase thermoelectric material and distinguishing nanoscale effects from those of a classical mixture. [ABSTRACT FROM AUTHOR]

Three novel inorganic–organic framework compounds containing the organic chromophore ligand 9-fluorenone-2,7-dicarboxylic acid (abbreviated H2FDC) and barium (BaFDC), cadmium (CdFDC) and manganese (MnFDC), respectively, have been synthesized and evaluated for their use as phosphor materials for solid state lighting and other applications. The results are compared with two earlier reported structures containing the same ligand with calcium (CaFDC) and strontium (SrFDC). The barium- and cadmium-containing compounds both show blue excited, yellow photoluminescence, while the manganese structure does not. The trends in luminescent efficiency for the Ba, Cd, Ca, and Sr derivatives are discussed in relation to crystallographic, optical, and low-temperature specific heat considerations. [ABSTRACT FROM AUTHOR]

Two isostructural hybrid inorganic-organic frameworks, M2(4,4′-bpy)(tfhba)2·4,4′-bpy, (M = Co (1), Zn (2); 4,4′-bpy = 4,4′-bipyridine; tfhba = 2,3,5,6-tetrafluoro-4-hydroxybenzoate) have been synthesized and their structures elucidated using single crystal X-ray diffraction. These materials are the first hybrid structures synthesized using the tfhba ligand. They contain a one-dimensional chain of corner-sharing MO4N trigonal bipyramids that has not been observed to date for Co2+ units. The magnetic properties of 1 have been investigated and indicate ferromagnetic ordering along the chains, with weak antiferromagnetic interactions between them. Overall the system is antiferromagnetic with a Nel temperature of 3 K, but undergoes a field-induced magnetic phase transition at 3 kOe. [ABSTRACT FROM AUTHOR]

The AZn2Sb2(P3m1, A= Ca, Sr, Eu, Yb) class of Zintl compounds has shown high thermoelectric efficiency (zT∼ 1) and is an appealing system for the development of Zintl structure–property relationships. High temperature transport measurements have previously been conducted for all known compositions except for SrZn2Sb2; here we characterize polycrystalline SrZn2Sb2to 723 K and review the transport behavior of the other compounds in this class. Consistent with the known AZn2Sb2compounds, SrZn2Sb2is found to be a hole-doped semiconductor with a thermal band gap ∼ 0.27 eV. The Seebeck coefficients of the AZn2Sb2compounds are found to be described by similar effective mass (m* ∼ 0.6 me). Electronic structure calculations reveal similar m* is due to antimony pstates at the valence band edge which are largely unaffected by the choice of A-site species. However, the choice of A-site element has a dramatic effect on the hole mobility, with the room temperature mobility of the rare earth-based compositions approximately double that found for Ca and Sr on the Asite. This difference in mobility is examined in the context of electronic structure calculations. [ABSTRACT FROM AUTHOR]

A new Os-based B-site ordered double perovskite with the chemical composition of Ca2ScOsO6 was successfully synthesized. The crystal structure of the title compound was determined by employing the powder X-ray diffraction method and was found to crystallize in the monoclinic P21/n space group with the cell constants of a = 5.4716(1) Å, b = 5.6165(1) Å, c = 7.8168 (1) Å, and β = 89.889 (2)°. The temperature-dependent magnetic susceptibility data suggest that this novel S = 3/2 compound undergoes an antiferromagnetic transition at ~69 K. Fitting the high-temperature susceptibility data (100-300 K) to Currie-Weisse behavior showed C = 1.734 emu·K/mol (μeff = 3.72 bohr magnetons) and = -341 K, which is indicative of dominant antiferromagnetic interactions. Temperature-dependent specific heat measurements exhibit a shape anomaly at 69 K, which is consistent with a long-range ordering of the spins. Because of a triangular arrangement of antiferromagnetically ordered magnetic ions, the system exhibits some degree of geometric magnetic frustration (GMF), but not strongly. Spin-dimer analysis, employing extended Hückel theory, reveals that a dominant exchange interaction exists (along the a crystallographic axis in perovskite layer), which violates the perfect condition for GMF. [ABSTRACT FROM AUTHOR]

Abstract: We report on the preparation and electrochemical characterization of Li2 M(SO4)2 (M =Co, Fe), where the Fe-based phase was previously unknown. Both compounds can be made at low temperatures (<320°C) and the Fe-based phase displays an open circuit voltage of 3.83V vs. Li+/Li0 for the Fe3+/Fe2+ redox potential. This corresponds to the highest voltage ever obtained for the Fe3+/Fe2+ redox couple in an iron-based, fluorine-free compound and is only matched by the triplite phase of LiFeSO4F. While the theoretical capacity of 102mA h g−1 will likely limit the commercial prospects for this phase, knowledge of the structure will provide useful insight into the structural origin of these increased potentials. [Copyright &y& Elsevier]

Abstract: CoAl2O4, CoGa2O4, and their solid solution Co(Ga z Al1− z )2O4 have been studied using high temperature oxide melt solution calorimetry in molten 2PbO·B2O3 at 973K. There is an approximately linear correlation between lattice parameters, enthalpy of formation from oxides, and the Ga content. The experimental enthalpy of mixing is zero within experimental error. The cation distribution parameters are calculated using the O’Neill and Navrotsky thermodynamic model. The enthalpies of mixing calculated from these parameters are small and consistent with the calorimetric data. The entropies of mixing are calculated from site occupancies and compared to those for a random mixture of Ga and Al ions on octahedral site with all Co tetrahedral and for a completely random mixture of all cations on both sites. Despite a zero heat of mixing, the solid solution is not ideal in that activities do not obey Raoult''s Law because of the more complex entropy of mixing. [Copyright &y& Elsevier]

Time-of-flight neutron powder diffraction and specific heat measurements were used to study the nature of thermal expansion in rhenium trioxide, an electrically conducting oxide with cubic symmetry. The temperature evolution of the lattice parameters shows that ReO3 can exhibit negative thermal expansion below room temperature and that the transition from negative to positive thermal expansion depends on sample preparation; the single crystal sample demonstrated the highest transition temperature, 294(19) K, and largest negative value for the coefficient of thermal expansion, α=-10(1)×10-7 K-1. For the oxygen atoms, the atomic displacement parameters are strongly anisotropic even at 15 K, indicative of a large contribution of static disorder to the displacement parameters. Further inspection of the temperature evolution of the oxygen displacement parameters for different samples reveals that the static disorder contribution is greater for the samples with diminished negative thermal expansion (NTE) behavior. In addition, specific heat measurements show that ReO3 lacks the low energy Einstein-type modes seen in other NTE oxides such as ZrW2O8. The thermal expansion behavior in other NTE materials such as ZrW2O8, cuprite-type oxides, and the Prussian blue cyanides are discussed and compared with that of our ReO3 samples. [ABSTRACT FROM AUTHOR]