Valence reduction process from sol–gel V2O5 to VO2 thin films

Highly orientated V2O5 thin films were prepared by sol–gel method on SiO2/Si substrate. The thin films of V2O5 were found converting to VO2 thin films under a temperature above 400 °C and a pressure below 2 Pa in air. It was observed that the reduction process follows the sequence as V2O5→V3O7→V4O9→V6O13→VO2, namely from VnO2n+1 (n=2–4,6) to VO2. Annealing the V2O5 thin film at 480 °C, under 1–2 Pa for 20 min, the VO2 polycrystalline thin film with the resistivity change larger than 3 orders through the transition temperature was obtained. The transition temperature was influenced by the heating condition in vacuum.