X-Ray Absorption Near Edge Structure and X-Ray Diffraction Studies of New Cubic CsVTeO5 and CsVTeO6 Compounds

The compounds CsVTeO 5 and CsVTeO 6 have been synthesized by solid-state reactions in an oxygen flow. CsVTeO 6 was decomposed to CsVTeO 5 at 550°C, and this CsVTeO 5 was re-transformed into CsVTeO 6 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. CsVTeO 6 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 CsVTeO 5 as in CsVO 3 and V 2 O 5 , which confirms that the local symmetry around the vanadium atom is highly distorted without an inversion center. The Rietveld refinement shows that CsVTeO 5 has the cubic symmetry (space group Fd3m) with a = 10.4842(2) Å, which is similar to the high-temperature polymorphic CsTiAsO 5 phase with highly distorted octahedral symmetry around the titanium atom.