Crystallization Mechanism and Phase Transition Properties of W-doped VO₂ Synthesized by Hydrothermal Method

Abstract

VO2 sol was firstly prepared using vanadyl sulfate as a vanadium source by precipitation-peptization method. Then tungsten(W) doping vanadium dioxide(W-VO2) was prepared by hydrothermal crystallization of prepared sol with the presence of ammonium metatungstate. The morphologies, crystal structure of the as-prepared samples and phase transition properties were studied by X-ray diffraction(XRD), field emission scanning electron microscope(FESEM)and differential scanning calorimetry(DSC) analysis. The results indicate that rod-like W-VO2(B) crystal with length of 1-2μm and radius of 100-200nm is firstly formed during hydrothermal treatment for 4-48h at 280℃, then the rod-like crystal dissolves gradually and sheet-like or snowflake-like crystal is formed with the phase transition from W-VO2(B) to W-VO2(M) and eventually, the W-VO2(M) crystals can further grow up while the W-VO2(B) gradually dissolves; the phase transition temperature of VO2 decreases with the increase in W doping content, and the phase transition temperature of W-VO2(M) reduces to about 28℃ when the nominal dopant concentration is 6.0%(atom fraction).The "nucleation-growth-transformation-ripening" mechanism is proposed as the formation mechanism based on the hydrothermal crystallization and morphological evolution process of W-VO2(M).

Keywords

• vanadium dioxide
• hydrothermal synthesis
• transition temperature
• tungsten doping