A metastable polymorph of vanadium sesquioxide was prepared by the reaction of vanadium trifluoride with a water-saturated gaseous mixture of 10 vol % hydrogen in argon. The new polymorph crystallizes in the bixbyite-type structure. At temperatures around 823 K a transformation to the well-known corundum-type phase is observed. Quantum-chemical calculations show that the bixbyite-type structure is about 9 kJ/mol less stable than the known corundum-based one. This result, in combination with the absence of imaginary modes in the phonon density of states, supports the classification of the bixbyite-type phase as a metastable V(2)O(3) polymorph. At ~50 K a paramagnetic to canted antiferromagnetic transition is detected.

Lithium aluminum oxide (γ-LiAlO 2 ) has been discussed and used for various applications, e.g., as electrode coating, membrane, or tritium breeder material. Although lithium-ion diffusion in this solid is essential for these purposes, it is still not sufficiently understood on the microscopic scale. Herein, we not only summarize and assess the available studies on diffusion in different crystalline forms of γ-LiAlO 2 , but also complement them with tracerdiffusion experiments on (001)-and conductivity spectroscopy on (100)oriented single crystals, yielding activation energies of 1.20(5) and 1.12(1) eV, respectively. Scrutinous crystal-chemical considerations, Voronoi− Dirichlet partitioning, and Hirshfeld surface analysis are employed to identify possible diffusion pathways. The one-particle potential, as derived from hightemperature powder neutron diffraction data presented as well, reveals the major path to be strongly curved and to run between adjacent lithium positions with a migration barrier of 0.72(5) eV. This finding is substantiated by comparison with recently published computational results. For the first time, a complete model for lithium-ion diffusion in γ-LiAlO 2 , consistent with all available data, is presented.

A sol-gel route for ternary lithium fluorides of transition metals (M) is presented allowing the synthesis of Li 3 MF 6 -type and Li 2 MF 5 -type compounds. It is based on a fluorolytic process using transition metal acetylacetonates as precursors. The domain size of the obtained powders can be controlled by modifying the conditions of synthesis. 6 Li and 7 Li magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy is used to study local environments of the Li ions in orthorhombic and monoclinic Li 3 VF 6 as well as Li 2 MnF 5 . The number of magnetically inequivalent Li sites found by MAS NMR is in agreement with the respective crystal structure of the compounds studied. Quantum chemical calculations show that all materials have high de-lithiation energies making them suitable candidates to be used as high-voltage battery cathode materials.

Fast ion conductors play one of the most important roles in solid state ionics as there is a great demand for their application in safe and powerful electrochemical energy storage systems. For such materials, it is known that the synthesis conditions may have significant impact on the final properties of the materials prepared. In this contribution, we made use of mechanosynthesis, carried out via high‐energy ball milling, to influence the ionic transport parameters of tetragonal, i.e., layer‐structured, BaSnF4. X‐ray powder diffraction (XRD) revealed that mechanical treatment of the binary fluorides BaF2 and SnF2 leads to a powder pointing to a nanocrystalline fluoride with (distorted) cubic symmetry. Differential scanning calorimetry (DSC) as well as preliminary in situ XRD measurements were used to follow the transformation towards the tetragonal modification with the composition BaSnF4. Broadband impedance spectroscopy was used to measure the overall electrical conductivity of the ternary fluoride. Remarkably, the layered form shows a room temperature conductivity of 7 × 10–4 S cm–1. Further emphasis was put on the characterization of the dielectric properties of the material, which was investigated by using different electrode materials to distinguish artefacts from intrinsic properties. Since we found a strong dependence of the real part of the permittivity on the electrode materials applied (carbon paste or sputtered Pt), we tend to assign the huge increase in permittivity, which was recently interpreted as giant dielectric constant, to interfacial polarization effects rather than to intrinsic properties. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Layer-structured materials, such as graphite (LiCy) or Lix(Co,Ni,Mn)O2, are important electrode materials in current battery research that still relies on insertion materials. This is due to their excellent ability to reversibly accommodate small alkali ions such as Li(+) and Na(+). Despite of these applications, microscopic information on Li ion self-diffusion in transition metal sulfides are relatively rare. Here, we used (7)Li nuclear magnetic resonance (NMR) spectroscopy to study translational Li ion diffusion in hexagonal (2H) LixNbS2 (x = 0.3, 0.7, and 1) by means of variable-temperature NMR relaxometry. (7)Li spin-lattice relaxation rates and (7)Li NMR spectra were used to determine Li jump rates and activation barriers as a function of Li content. Hereby, NMR spin-lattice relaxation rates recorded with the spin-lock technique offered the possibility to study Li ion dynamics on both the short-range and long-range length scale. Information was extracted from complete diffusion-induced rate peaks that are obtained when the relaxation rate is plotted vs inverse temperature. The peak maximum of the three samples studied shifts toward higher temperatures with increasing Li content x in 2H-LixNbS2. Information on the dimensionality of the diffusion process was experimentally obtained by frequency dependent Rρ measurements carried out at T = 444 K, that is in the high-temperature regime of the rate peaks. A slight, but measurable frequency-dependence within this limit is found for all samples; it is in good agreement with predictions from relaxation models developed to approximate low-dimensional (2D) jump diffusion.