Abstract
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 W doping 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 W ions doping in the V1−xWxO2 system.
Highlights
Vanadium oxides have nearly 15–20 stable phases, metalinsulator transition (MIT) has been reported in at least 8 vanadium oxide compounds (V2O3, VO2, V3O5, V4O7, V5O9, V6O11, V2O5, V6O13, etc.) at temperatures ranging from −147◦C to 68◦C [1,2,3], in which VO2 materials show the fully reversible phase transition between monoclinic VO2 (M) and tetragonal rutile phase VO2 (R) fascinatingly around 68◦C
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 reduction of transition temperature is estimated to be about 17 K per 1 at% of W doping with the tungsten extents of ≤1 at%, but only 9.5 K per 1 at% with the tungsten extents of >1 at%
Summary
Vanadium oxides have nearly 15–20 stable phases, metalinsulator transition (MIT) has been reported in at least 8 vanadium oxide compounds (V2O3, VO2, V3O5, V4O7, V5O9, V6O11, V2O5, V6O13, etc.) at temperatures ranging from −147◦C to 68◦C [1,2,3], in which VO2 materials show the fully reversible phase transition between monoclinic VO2 (M) and tetragonal rutile phase VO2 (R) fascinatingly around 68◦C. As an intelligent window material, the study of Wdoped VO2 mainly focused on thin films and nanoparticles It has been prepared by a variety of methods involving excimer-laser-assisted metal organic deposition (ELAMOD) [19], magnetron sputtering [20], chemical vapor deposition (CVD) [21], pulsed laser deposition (PLD) [22], and vacuum evaporation [23]. Seems to be an alternative solution to the above problems due to its low cost and the option of metal doping This method usually requires specific raw materials or pretreatments which limit their practical applications [6]. We report a simple solution-based process to prepare pure VO2 and W-doped VO2 nanopowders with cheap and nontoxic vanadium (V) precursors and short reaction times. Doping with tungsten could adjust the phase transition temperature remarkably, and put the thermochromic application into practice
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