Study On W-doped Vanadium Dioxide Film Prepared By An Inorganic Sol-gel Method

Vanadium dioxide is a kind of heat sensitive functional material, astemperature rising, phase transition will occur at about 68℃from semiconductorof monoclinic structure to metal of orthogonal structure. At the same time, somephysical properties such as electrical conductivity and spectrum transmittion willshow an abrupt change. Because VO₂ posses these properties, it is widely used ininformation storage, photoelectric switch, intelligent window materials and so on.The adulteration of little other elements can effectively change the phase transitiontemperature. Especially the adulteration of higher value ion can lower the phasetransition temperature. Among all of those ions, the effect of W⁶⁺ is much betterthan others.In this research, to prepare vanadium dioxide thin film with low phasetransition temperature close to room temperature, prepare methods include asfollows process. Firstly, quenching method was used to prepare V₂O₅ sol andWO₃ sol was prepared by tungsten powders reacting with H₂O₂. Secondly, someWO₃ sol was mixed into V₂O₅ sol, and dip-doped method was used to prepare filmon clean glass slide. Thirdly, the film was dry. Finally, the film the film wasdeoxidized by H₂ or H₂-H₂O equilibrium method, then the W-doped VO₂ film wasprepared. In this experiment, optical microscope, X-ray diffraction, XPS, IRspectrophotometer, four-step equipment and etc were used to detect the surface, theelectric and optic properties of the film. The results showed that:(1)W adulteration is achieved successfully by preparing mixed sols.(2)V-W mixed sols and dip-doped method are used to prepare V₂O₅ thin filmon glass slide. W-doped VO₂ thin film is prepared successfully by deoxidized in H₂atmosphere. The better process conditions of preparing this kind of film is: dryingat 200℃for 2 hours, heat treatment at 300-350℃in H₂ atmosphere for 3.5 hours.(3)According to the study on the phase transition temperature of W-dopedVO₂ thin film, the result shows that the W-doped VO₂ film prepared by sol-gel,when W:V(mol ratio ) is 1.5:100, the S-M phase transition temperature can belowed to close to about 30℃.(4)When the temperature is close to the S-M phase transition temperature, theresistance and the IR transmission of the W-doped VO₂ thin film have a notablechange, and IR transmission weakened when the W content increase.(5)According to the calculation of thermodynamics, at certain temperature,increasing vapor pressure (P_H2O/P_H2) can effectively restrain the deoxidized ofWO₃. When the temperature is 400℃, if the value of P_H2O/P_H2 is over 6.42, thedeoxidized reaction of WO₃ can't carry on.(6)At 350℃, deoxidized for 3h, control the P_H2O/P_H2 through keep thetemperature of water at 50℃, the S-M phase transition temperature of VO₂ filmprepared by this method is about 33℃, and near the phase transition temperature,the resistance has a notable change.(7)The experiment improve that though the process of sol-gel method torealize W adulteration is simple and the cost is low, but it also has shortagewitch is the mixed sols agglomerate quickly when W content is over 2%(molratio). Therefore the fitting range of W adulteration by the sol-gel method isunder 2% (tool ratio).