Studies On Thermochromic Properties Of Doped VO₂ Thin Films Prepared By A Novel Sol-Gel Method

Thermochromic vanadium dioxide?VO₂?has attracted much attention due to its reversible metal-insulator transition?MIT?around 68?.Vanadium dioxide and W/Eu doped films were grown successfully by Sol-Gel method followed with the process of annealing under high vacuum.Finally,the transition temperature of the VO₂ films was decreased dramatically with excellent infrared regulation performance.The detailed process of samples prearation is as follows:a certain amount of V₂O₅ and oxalic acid were added to isobutanol,and the mixture was stirred for 6-10h under water bath at 80?.A blue-green solution was obtained.The pre-deposited films were obtained by means of spin coating.Next,the pre-deposited films were annealed at 450-530?for 4h with the vacuum of 10^-3Pa and transformed to VO₂ films.The RT and IR were utilized to study photoelectric properties of VO₂ films and it is indicated that the transition temperature of the samples were reduced below 68?,with the transition width of around20?.Meanwhile,its infrared behavior could reach to above 45%.Then,the transparent solution in which the tungstic acid and hydrogen peroxide reacted with each other was added into the isobutanol including V₂O₅ and oxalic acid.The W-doped VO₂ films were grown after spinning and annealing.The resistance abruptness and IR performance were weakened despite W-doping effectively depressed transition temperature.When the annealing temperature was increased to 500?,the IR performance was improved distinctly reaching to 40%below and above transition temperature.The Raman spectra dependence of temperature shows that the W doping can't lead to the appreance of M2 phase during the process of the phase transition.Moreover,the W and Eu co-doped VO₂ films were researched firstly,and the characterizations show Eu has little influence on transition temperature of VO₂ films but dramatically improve infrared adjustment ability before and after the phase transition.As for 3%Eu and 1%W co-doped VO₂ thin films,the transition temperature was reduced to 43?and infrared transmittance change is over 60%.It is indicated that low-valent transition metal can improve infrared performance of W-doped VO₂ films.