Hydrothermal Preparation Of VO₂ Powder And Its Properties Modification By Doping Rare Earth

Vanadium oxides usually undergo phase transition between metals and semiconductors under heating conditions,but the temperature of phase transition is different.VO₂ is a functional material of typical thermal induced phase transition.The reversible phase transition between metal phase and semiconductor phase occurs near68?.The crystal structure changes from tetragonal phase to monoclinic phase during phase transition,which leads to the mutation in optical,electrical and magnetic.The VO₂ has wide application prospects in photoelectric equipment,infrared detection,temperature control switch and intelligent glass materials.The thermal phase transition temperature of VO₂ usually is far higher than room temperature,and the reduction of phase transition temperature is the premise of its application.The methods of reducing the phase transition temperature include improving the preparation process of VO₂ or doping modification.In this paper,based on the principle that element doping can effectively reduce the phase transition temperature,the doping experiments of VO₂ materials were emphasized.?1?VO₂ powder materials were prepared by hydrothermal synthesis method.The optimum parameters for preparing VO₂ precursor were studied by using pure V₂O₅ as raw materials,C₂H₂O₄·2H₂O as reductant and H₂NCONH₂ as precipitant.The results indicated that the appropriate technological parameters were as follows:the ratio of V₂O₅ and C₂H₂O₄ is 1:2,the hydrothermal temperature is 190?,the hydrothermal time is 3 days and the filling degree of the hydrothermal reactor is 70%.?2?VO₂?M?powders can be prepared by drying and heat treatment on the precursor of VO₂?B?.The appropriate heat treatment conditions were obtained through experiments:the temperature is 800?and the time is 5h.?3?The microstructure and composition of VO₂ were analyzed by means of XRD,SEM,particle size analysis,EDS and DSC.The morphology of the VO₂ is spherical like,the particle size distribution is about 200⁷00nm,and the phase transition temperature is about 73.58?.The experiment shows that this method has high purity,small particle size.?4?The effects of Y³⁺,La³⁺and Ce³⁺doping on phase transformation temperature of VO₂ were studied.The results show that the doping of Y³⁺,La³⁺and Ce³⁺can reduce the temperature of VO₂ phase transition,and the temperature drop increases with the increase of the doping concentration of rare earth elements.Y³⁺doping concentration was 3.6%,8.6%and 15.8%,the phase change temperature dropped to 65.28?,65.10?and 61.62?respectively;La³⁺doping concentration was 2.2%,5.4%and 10.3%,the phase change temperature dropped to 66.53?,64.53?and 63.71?respectively;Ce³⁺doping concentration was 2.2%,5.4%and 10.3%,the phase change temperature dropped to 67.23?,66.53?and 64.76?respectively.