From VO2(B) to VO2(A) nanorods: Hydrothermal synthesis, evolution and optical properties in V2O5H2C2O4H2O system

Pure phase VO2(A) nanorods have been synthesized by hydrothermal in V2O5H2C2O4H2O system. One group samples were prepared by varying the system temperature under a certain filling ratio (f = 0.40) and reaction time for observing the formation and evolution of VO2(A) and VO2(B) phase. The composition and morphology of the nanorods were characterized using X-ray diffraction (XRD), scanning electron microscopies (SEM), Fourier transform infrared spectroscopy (FTIR) and Raman spectrum, respectively. Experiments showed the VO2(B) phase were firstly formed and then it transformed into VO2(A) as increasing hydrothermal reaction temperature from 180 °C to 230 °C. For our VO2(A) nanorods, the phase transition temperature could be observed by differential scanning calorimetry (DSC) measurement, 171.7 °C was higher than that of 162 °C for VO2(A) phase, which might be ascribed to the lower crystallinity or nonstoichiometry in VO2(A) nanorods.