Chunming Huang

Synthesis of thermochromic W-doped VO 2 (M/R) nanopowders by a simple solution-based process

Thermochromic W-doped VO2 nanopowders were prepared by a novel and simple solution-based method and characterized by a variety of techniques. We mainly investigated the effect of tungsten dopant on the structural properties and phase transition of V1-xWxO2. The as-obtained nanopowders with tungsten content of ≤ 2.5 at% can be readily indexed as monoclinic VO2 (M) while that of 3 at% assigned into the rutile VO2 (R). The valence state of tungsten in the nanopowders is +6. TEM and XRD results show that the substitution of W atom for V in VO2 results in a decrease of the d space of the (011) plane. The phase transition temperature is determined by differential scanning calorimetry (DSC). It is found, for the first time, that the reduction of transition temperature reaches to 17 K per 1 at% of Wdoping with the tungsten extents of ≤1 at%, but only 9.5 K per 1 at% with the tungsten extents of >1 at%. The reason of this arises from the difficulty of the formation of V3+-W4+ and V3+-W6+ pairs by the increasing of Wions doping in the V1-xWxO2 system.