Preparation Of Vanadium Dioxide And Its Phase Transition Properties

Vanadium dioxide (VO2) is belonged to metal oxides,it is also a function of material with a special property that at about341K,it will occurs phase-transition, from a low temperature phase change to a high temperature phase metal (semiconductor insulator).The phase-transition is reversible. After phase-transition,the physical and chemistry features of VO2will subsequently mutated, because of the mutation characteristics, Vanadium dioxide has a wide range of potential applications.The temperature of phase transition will change due to scaling and doping,so that the vanadium dioxide is aroused great interest at present.In this experiment, the method of experiment is based on sol-gel method and hydrothermal method, combining with the advantages of both two methods to preparing high purity VO2powder.The experimental raw material is V2O5powder, the first step of experiment was preparing V2O5sol using sol-gel method,then preparing purer VO2powder in which ethyl alcohol absolute and oxalic acid were used as reducing agent.we analysed the factors which have effect on the morphology of VO2through changing experimental parameters. The second step of experiment was preparing doped vanadium dioxide powder using V2O5sol, oxalic acid was used as reducing agent, sodium tungstate and lanthanum acetate were used as the doping agent,W-doped powder and La-doped powder were prepared.Finally, the two experimental products were tested and analysed. The main results are listed as follows:(1) In this experiment high purity VO2powder were prepared through combining with sol-gel method and hydrothermal method(2) The kind of reducing agent, dosage of reducing agent, temperature of the reaction, pH value of the reaction will have impact on crystal morphology of VO2When oxalic acid was used as reducing agent, furfuraceous VO2crystal were prepared. The best experimental conditions of preparing VO2were:n (oxalic acid):n (V2O5)=2:1, pH of the solution is3, the temperature of the reaction is200℃; When anhydrous ethanol was used as reducing agent, Rod-shaped VO2crystal were prepared. The best experimental conditions of preparing VO2were:n (oxalic acid):n (V2O5)=2:1, pH of the solution is7, the temperature of the reaction is200℃(3) Vanadium dioxide could be effectively doped by lanthanum acetate and sodium tungstate. Doping had a certain degree for the morphology and phase transition temperature of vanadium dioxide. Lanthanum acetate as a dopant, La doped had little effect on the morphology of single vanadium dioxide crystal. Which just maked the entire ordered crystal morphology change, becoming disorderly. VO2phase transition temperature was followed the amount of doped La increasing which assumed non-linear increasing trend. VO2-La phase transition temperature trends equation was as follows:y=35.086x3-96.697x2+177.25x+338.39,R2=0.9966Sodium tungstate as a dopant, there was produced a greater impact for vanadium dioxide crystal morphology with W-doped. Which maked the vanadium dioxide crystal morphology change from better dispersion sheet to irregular pieces of fragmentation shape. VO2phase transition temperature was followed the amount of doped W increasing which assumed non-linear increasing trend., V02-W phase transition temperature trends equation was as follows:y=-0.0392x3+0.3950x2-7.5322x+67.424,R2=0.9933...