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

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 (V2O5-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.