A new lithium vanadium fluoride Li2VF6 was prepared by reacting lithium fluoride LiF with vanadium tetrafluoride VF4 in a monel capsule at 500 °C. The crystal structure has been determined by means of powder X-ray diffraction. Trirutile-type dilithium hexafluorovanadate(IV) crystallizes in the tetragonal space group P42/mnmwith lattice parameters a=459.99(1), b=459:99(1), c=896.64(2) pm. The presence of a Jahn-Teller effect is discussed.
The new niobium oxide fluorides MNbO2F4 [M = (Cr, Fe)], CrNb2O4F5, and Fe2Nb3O6F9 were prepared by treatment of chromium or iron nitrate with Nb-containing hydrofluoric acid solutions. Crystal structures were investigated by means of X-ray powder diffraction. All new compounds can be structurally refined in the cubic ReO3-type. The iron niobium oxide fluorides are reddish orange, and chromium containing phases exhibit a light green color. The niobium atoms are in the highest formal oxidation state.
29 July 2013 in Zeitschrift für Kristallographie - Crystalline Materials
Li x Na2−x Ti6O13has received attention as 3d-metal oxide based anode material for possible battery application. Generally, titanium oxides represent excellent Li hosts due to their zero-strain behavior, cycling stability and high operating voltage. New developments choose Na as charge carrier, but less effort is put in the investigation of mixed cation conductors. Owing to the synthesis route of Li x Na2−x Ti6O13(0 ≤ x ≤ 2) the coordination of Na and Li in the channels is different which had been investigated by means of X-ray and neutron diffraction. Up to now, no Raman spectroscopy has been applied. This oxide is highly Raman-active, thus the local structure can also be analyzed in terms of vibrational spectroscopy. Micro-Raman spectroscopy carried out at room temperature with different cation contents (x = 0, 0.33, 1, 2) shows the continuous change from Na to Li by a superposition of the modes for Na2Ti6O13 and Li2Ti6O13. The only exceptions are two distinct modes. They appear either for Li (118 cm –1) or Na (135 cm –1). The results confirm the high-temperature phase stability of Na2Ti6O13 as well as the anisotropic thermal expansion of the unit cell seen by in situ X-ray powder diffraction under two different gas atmospheres. Combining these results, we suppose that the anisotropic thermal expansion of the lattice parameters is affected by the normal vectors of the corresponding bond vibrations in Na2Ti6O13 and Li2Ti6O13. Crystalline-orbital calculations of the Raman shifts of Li x Na2−x Ti6O13were carried out for the cation contents x = 0, 1, 2 and Raman modes were assigned to specific bond vibrations supported by theory. Besides, this gives additionally information about the Li/Na ratio in a new and simple way.
22 August 2012 in Zeitschrift für anorganische und allgemeine Chemie