Insights into the phase transition behavior of thermochromic VO2 (M1) powders doped with Tungsten

Abstract

Tungsten (W) is one of the most effective elements in regulating the metal–insulator transition (MIT) temperature of VO₂(M1). W-doped VO₂ thus shows broader application prospects. However, some issues related to phase transitions affected by W doping remain unclear. Here, the phase transition temperature of VO₂ is tuned between −34.8 and 66.0 °C by changing the W concentration, spanning approximately 100 °C. Gaussian fitting for the (011) peak of VO₂(M1) reveals its structure transition from the monoclinic phase to the tetragonal phase in W-doped VO₂ powder. Lattice distortion is demonstrated to be the primary cause of the reduced critical transition temperature (T_c) because of a slower T_c decrease in mixed-phase VO₂. In addition, W-doped VO₂ powder exhibits doping-level dependent structure instability, leading to a further reduction in T_c, e.g., a 5 °C decrease for W1.5. Subsequent thermal cycling indicates that the T_c stabilizes after three cycles. These W-doped VO₂ powders are used to prepare thermochromic films, where 1.0 at.% W-doped VO₂ films show optimal thermochromic performance with a T_c closer to room temperature, making it more ideal for smart windows compared to the undoped film. This work will offer valuable theoretical insights and data references for the future doping engineering design and practical applications of VO₂.