Lowered phase transition temperature and excellent solar heat shielding properties of well-crystallized VO2 by W doping.

Monoclinic VO2 (M) is a key material for energy-efficient smart window applications. Fine crystalline VO2 particles with an ambient phase transition temperature are urgently required to achieve excellent properties including high luminous transmittance and solar heat shielding ability. Moreover, the anti-oxidation ability is regarded as a significant factor which determines the lifetime of VO2-based products. In this paper, well-crystallized W-doped VO2 with low phase transition temperature, excellent solar heat shielding ability and considerable anti-oxidation ability was synthesized by a solid-state reaction process. The phase transition temperature was reduced from 67.3 °C to 10.8 °C at 2.0% W doping with an efficiency of -28.1 °C per at%. Importantly, an excellent balance between the phase transition temperature and the latent heat was obtained at high doping levels (1.5-2.0%). Furthermore, W-doped VO2 particles exhibited a significantly longer exposure time (more than 5 h) at 300 °C in air than the previously reported 2 h in the literature, and the corresponding derived composite foils showed excellent luminous transmittance and solar heat shielding properties (Tlum = 49.9% and Tsol = 44.8% for 2.0% W doping).