Investigation On Synthesis And Optical Properties Of Vanadium Dioxide Nanopowders

VO2is a typical thermochromic compound. It exhibits a semi-conducting tometallic phase transition at68。C，involving strong variations in electrical, magnetic,optical transmittance in the IR region. The most important is that phase-transitiontemperature (Tc) of VO2powders can be gone down to room temperature bydoping. So VO2call be used for a smart window material and energy saved material.This paper reports that co-doped vanadium dioxide nanopowders weresynthesized by hydrothermal method with active white powdery tungstic acid (WPTA)and sodium molybdate used as a substitutional dopant. It was found that this methodwas a valuable preparation technique for its cheap precursor, simple processes, can bedoped tungsten easily, and great potential to produce markedly high qualitynanopowders. The characterization and analysis of terminal resultant were determinedby XRD, XPS, TEM, DSC and FI-IR. The properties of thermochromic VO2nanopowders have been investigated by FT-IR and the four-probe method.The results show that the VO2particle size is about25?35nm. Both ofhydrothermal reaction temperature and time make a difference on crystal texture.Optimal conditions were found as, reaction temperature280°C, reaction time44hourand80%ifll. And we found that powders with W doping amount higher than6%isnot VO2anymore. The higher the doping content is, the lower the phase transitiontemperature. But the infrared transmittance decreases and then increases at3%W. Tobalance the phase transition temperature with infrared transmittance, we conclude thatthe optimal Tungsten atom doping content is3%. The phase transition temperature ofVO2powders co-doped with3%W and2%Mo is decreased to25.5°C, which is veryclose to the room temperature. The contrast of its transmission measured at20°C and30。C by FTIR below and above the phase-transition temperature is60%. And itschange in resistance covers1.8orders of magnitude. Based on the above, we drawconclusions that co-doping with tungsten and molybdenum will greatly improve theoptical performance of VO2.