| Summary: | The doping of tungsten into VO<sub>2</sub> (M) via a polyol process that is based on oligomerization of ammonium metavanadate and ethylene glycol (EG) to synthesize a vanadyl ethylene glycolate (VEG) followed by postcalcination was carried out by simply adding 1-dodecanol and the tungsten source tungstenoxytetrachloride (WOCl<sub>4</sub>). Tungsten-doped VEGs (W-VEGs) and their calcinated compounds (W<sub>x</sub>VO<sub>2</sub>) were prepared with varying mixing ratios of EG to 1-dodecanol and WOCl<sub>4</sub> concentrations. Characterizations of W-VEGs by powder X-ray diffraction, differential scanning calorimetry, scanning electron microscopy, and infrared and transmittance spectroscopy showed that tungsten elements were successfully doped into W<sub>x</sub>VO<sub>2</sub>, thereby decreasing the metal-insulator transition temperature from 68 down to 51 °C. Our results suggested that WOCl<sub>4</sub> variously combined with 1-dodecanol might interrupt the linear growth of W-VEGs, but that such an interruption might be alleviated at the optimal 1:1 mixing ratio of EG to 1-dodecanol, resulting in the successful W doping. The difference in the solar modulations of a W<sub>0.0207</sub>VO<sub>2</sub> dispersion measured at 20 and 70 °C was increased to 21.8% while that of a pure VO<sub>2</sub> dispersion was 2.5%. It was suggested that WOCl<sub>4</sub> coupled with both EG and 1-dodecanol at an optimal mixing ratio could improve the formation of W-VEG and W<sub>x</sub>VO<sub>2</sub> and that the bulky dodecyl chains might act as defects to decrease crystallinity.
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