Hydrothermal Synthesis of CsxWO3 and the Effects of N2 Annealing on its Microstructure and Heat Shielding Properties

Cesium tungsten bronze (CsxWO3) powders were synthesized by hydrothermal reaction at 190 °C by using sodium tungstate and cesium carbonate as raw materials, and the effects of N2 annealing on the microstructure and near-infrared (NIR) shielding as well as heat insulation properties of CsxWO3 were investigated. The results indicated that the synthesized CsxWO3 powders exhibited hexagonal Cs0.32WO3 crystal structure, and subsequent N2 annealing could further improve the crystallinity of CsxWO3 particles. Moreover, the NIR shielding and heat insulation properties of CsxWO3 could be further improved after N2 annealing at appropriate temperature for a period of time. Particularly, the 500 °C-annealed CsxWO3 products in the N2 atmosphere showed the best NIR shielding and heat insulation properties. When the N2 annealing temperature was higher than 700 °C, the NIR shielding properties decreased again. The 800 °C-annealed samples in the N2 atmosphere showed higher visible light transmittance, however, the NIR shielding properties were lower than that of the non-annealed samples.