X-ray absorption near edge structure and X-ray diffraction studies of new cubic CsVTeO5 and CsVTeO6 compounds

The compounds CsVTeO5 and CsVTeO6 have been synthesized by solid-state reactions in an oxygen flow. CsVTeO6 was decomposed to CsVTeO5 at 550 degrees C, and this CsVTeO5 was re-transformed into CsVTeO6 under high oxygen pressure. The local structure around vanadium and its Valence state have been studied by X-ray absorption near edge structure spectroscopy at the vanadium K-edge. CsVTeO6 shows a weak peak at the pre-edge region, which indicates that the vanadium is stabilized in an octahedral site as expected in normal AB(2)O(6) pyrochlore. On the other hand, a strong pre-edge peak appeared in CsVTeO5 as in CsVO3 and V2O5, which confirms that the local symmetry around the vanadium atom is highly distorted without an inversion center. The Rietveld refinement shows that CsVTeO5 has the cubic symmetry (space group Fd (3) over bar m) with a = 10.4842(2) Angstrom, which is similar to the high-temperature polymorphic CsTiAsO5 phase with highly distorted octahedral symmetry around the titanium atom.