W掺杂二氧化钒的水热晶化机理及其相变性能

以硫酸氧钒为钒源,采用沉淀-胶溶法制备VO_2溶胶。然后向溶胶中加入偏钒酸铵,利用溶胶水热晶化制备出W掺杂二氧化钒(W-VO_2,M相)粉体。通过XRD,FESEM和DSC对合成产物的物相组成、形貌和相变性能进行研究。结果表明:在280℃条件下水热处理4~48h,VO_2溶胶经过水热晶化生成长约1~2μm、直径约100~200nm棒状W-VO_2(B)晶体,伴随着B相向M相晶型转变,W-VO_2(B)逐渐消溶,而W-VO_2(M)逐渐长大,形貌由棒状转变为片状或雪花状;W-VO_2(M)相变温度随着W掺杂量增加而降低,当名义掺杂量为6.0%(原子分数)时,相变温度降低到28℃。根据水热晶化和形貌演变过程,提出了W-VO_2(M)可能的"形核-生长-转化-熟化"形成机理。

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

VO2 sol was firstly prepared using vanadyl sulfate as a vanadium source by precipitationpeptization 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-growthtransformation-ripening" mechanism is proposed as the formation mechanism based on the hydrothermal crystallization and morphological evolution process of W-VO2 (M).