Fig. 3

Chemical analysis and electrical properties. a XRD patterns for NP c-V₂O₃, r-VO₂ and c-V₂O₃/r-VO_2−x films, demonstrating the evolution of phase transformation via thermal oxidation of the corundum c-V₂O₃ at 300 °C for 10 (A), 20 (B), 30 (C) and 60 min (D), respectively. The line patterns show reference cards 34–0187 and 44–0253 for the pristine c-V₂O₃ and r-VO₂ according to JCPDS. b–d XPS spectra of O 1s, and V 2p for NP c-V₂O₃ (a), c-V₂O₃/r-VO_2−x (b) and r-VO₂ films (c), which are synthesized by thermal oxidation of the as-prepared c-V₂O₃ films for 0, 10, 90 min at 300 °C, respectively. e I–V curves and the corresponding resistances (inset) of NP c-V₂O₃, c-V₂O₃/r-VO_2−x (x = 0.22) and r-VO₂ films