STRUCTURE AND PROPERTIES OF AMORPHOUS V2O5

Pure non-stoichiometric amorphous vanadium pentoxide (V2O5) has been made by splat cooling from the melt. The vanadium coordination is analysed by infrared spectroscopy, X-ray absorption at the vanadium K edge (X-ray adsorption near-edge structure and extended X-ray absorption fine structure) and V-51 solid-state nuclear magnetic resonance. All these techniques show that V5+ ions exhibit both fourfold VO4 and fivefold VO5 coordination states. Electron spin resonance experiments show that unpaired electrons are localized on V4+ sites surrounded by five oxygen atoms as in crystalline V2O5. The amount of VO4 structural units in the amorphous oxide depends on experimental parameters such as temperature, quenching rate or water pressure. These observations could provide a clue to explain the controversies found in the literature concerning the vanadium coordination, the electrical conductivity and the chemical reactivity of V2O5-based amorphous compounds.