The Vibrational Spectra of VPO5 Crystal Phases and Related Glasses

Abstract

Infrared and Raman spectra were measured and interpreted for two crystalline VPO5 phases (α- and β-VPO5) and several related vanadium phosphate glasses. The spectral results for the crystalline phases were consistent with those predicted by factor group analysis using the previously determined space groups. Empirical band assignments were made for the observed bands on the basis of the bands observed earlier for related phosphate and oxyvanadium compounds. Also, the band assignments made for the infrared spectra of the glasses were consistent with the assignments for crystalline V2O5 and the two crystalline VPO5 phases. No Raman spectra were observed for the glasses because processes involving adsorption and Rayleigh scattering dominated over Raman scattering. The infrared spectra of vanadium phosphate glasses with high P2O5 concentrations possessed many features resembling those observed in the infrared spectra of α-VPO5, suggesting similarities in the short range order for the two materials. Analyses of the vibrational spectra of hydrated α-VPO5 samples suggests that the water molecules are adsorbed in the interlamellar spaces of the crystals, complexing to vanadium ions. Initial steps in the hydration of vanadium phosphate glasses apparently involve physical adsorption of water on their surfaces. No water adsorption could be detected for β-VPO5 under normal conditions from its infrared and Raman spectra.