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

Thermochromic W-doped VO ₂ 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 V _1-x WxO ₂. The as-obtained nanopowders with tungsten content of ≤2.5 at can be readily indexed as monoclinic VO ₂ (M) while that of 3 at assigned into the rutile VO ₂ (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 VO ₂ 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 17K per 1 at of W doping with the tungsten extents of ≤1 at, but only 9.5K per 1 at with the tungsten extents of 1 at. The reason of this arises from the difficulty of the formation of V ³⁺ - W ⁴⁺ and V ³⁺ - W ⁶⁺ pairs by the increasing of W ions doping in the V _1-x W x O ₂ system.