Hydrothermal Systhesis Of VO₂?M? And Its Structure And Properties Study

Vanadium dioxide?VO₂? has attracted great attention due to its particular reversible thermal-induced metal-insulator transition near room temperature. Because of the particularity of vanadium and its oxide, the preparation of pure phase VO₂ is difficult.VO₂ nanoparticles were systhezed using ammonium metavanadate and oxalic acid via a hydrothermal reaction&annealing two-step method with various annealing temperature or annealing time. And it was characterized by X ray diffraction?XRD?, differential scanning calorimetry?DSC?, Raman scattering, X-ray Photoelectron Spectroscopy?XPS?, and the structure and properties of samples were discussed.Research on VO₂ with different annealing temperature shows: the precursor,systhesized by the first step hydrothermal reaction, which was proved as VO₂?B? in XRD,began to transform into VO₂?M? when the annealing temperature approacching 500? and transformed completely at 550 ? and oxidized into V6O13 over 550 ?. Moreover, as annealing temperature rising, the crystalline quality and grain size of VO₂ product increased and weight of hysteresis loop reduced. As annealing temperature was 550?, integral area in DSC was maximizing and it came the best loop of resistance-temperature, however, the product can be oxidized in air atmosphere. Hence, 550? should be the optimal value of annealing temperature.Research on VO₂ with different annealing time shows:precursor was annealed at550? with different annealing time?3h,6h,12 and 24h? and as-prepared product presented as VO₂?M? in XRD. As annealing time increased, the mean grain size increased and the weight of hysteresis loop, latent heat of phase transition and phase-transition temperature of VO₂ product decreased. By means of IR curves, it was learned that 6h product had the best optical performance and its resistance properties change rate of 2 orders of magnitude before and after the phase transition.Based on the analysis of all data, annealing for 6h near 550 ? may be the optimal configuration of the hydrothermal reaction-annealing two-step method.