Structural studies of V2O5–WO3 and WO3–V2O5 solid solutions

Abstract

Powder X-ray diffraction, Fourier transform Raman spectroscopy, solid-state NMR and X-ray photoelectron spectroscopy were used to determine the composition and structure of a mixed oxide containing 10 mol% V₂O₅ and 90 mol% WO₃. The parent sample consists of hybrid crystallites of a tungsta-bronze isostructural with tetragonal WO₃ but containing atomic vanadium in the bulk of the crystals and V(III) in the surface region, and of small crystals of strongly reduced vanadia-like surface species (V₂O_5–x with x=0.42). Further thermal treatment causes progressive surface segregation of vanadium from the V₂O₅–WO₃ solid solution, accompanied by the formation of a WO₃–V₂O₅ solid solution and partial tetragonal–monoclinic structural transformation of the bronze.