Abstract
The doping of tungsten into VO2 (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 (WOCl4). Tungsten-doped VEGs (W-VEGs) and their calcinated compounds (WxVO2) were prepared with varying mixing ratios of EG to 1-dodecanol and WOCl4 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 WxVO2, thereby decreasing the metal-insulator transition temperature from 68 down to 51 °C. Our results suggested that WOCl4 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 W0.0207VO2 dispersion measured at 20 and 70 °C was increased to 21.8% while that of a pure VO2 dispersion was 2.5%. It was suggested that WOCl4 coupled with both EG and 1-dodecanol at an optimal mixing ratio could improve the formation of W-VEG and WxVO2 and that the bulky dodecyl chains might act as defects to decrease crystallinity.
Highlights
Smart windows that use the thermochromic property of vanadium dioxide (VO2 ) have been highlighted as a promising energy saving technology due to their selective control over the transmission of heat rays that enhances energy saving efficiency [1]
One might expect that WOCl4 combined with ethylene glycol (EG) participates in the formation of vanadyl ethylene glycolate (VEG), thereby might expect that WOCl4 combined with EG participates in the formation of VEG, thereby resulting resulting in the insertion of tungsten atoms into VO2 (M) during calcination
We carried out the synthesis of tungsten-doped VO2 via a polyol method based on ammonium metavanadate and EG by utilizing WOCl4 and 1-dodecanol as the tungsten source and capping agent, respectively
Summary
Smart windows that use the thermochromic property of vanadium dioxide (VO2 ) have been highlighted as a promising energy saving technology due to their selective control over the transmission of heat rays that enhances energy saving efficiency [1]. At 68 ◦ C or below, VO2 has a monoclinic structure (M) with a semiconducting property, and at temperatures above 68 ◦ C, its crystal structure is transformed to a tetragonal rutile structure, accompanying a change in its electrical property from semiconducting to metallic [2]. This metal-insulator transition (MIT) enables VO2 to selectively reflect near-infrared light (NIR) due to its metallic property above its MIT temperature while transmitting visible light [3].
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