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

• A tunable MIT temperature of VO 2 between -34.8 °C and 66.0 °C is achieved by W doping, spanning approximately 100 °C. • In situ XRD reveals a gradual monoclinic-to-tetragonal structure transition in W-doped VO 2 powder upon heating. • Doping-level dependent structure instability of W-doped VO 2 powder is uncovered, resulting in a further reduction in T c . • 1.0 at.% W-doped VO 2 film is ideal for smart windows due to its optimal thermochromic performance and lower T c (43.6 °C). Tungsten (W) is one of the most effective elements in regulating the metal–insulator transition (MIT) temperature of VO 2 (M1). W-doped VO 2 thus shows broader application prospects. However, some issues related to phase transitions affected by W doping remain unclear. Here, the phase transition temperature of VO 2 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 VO 2 (M1) reveals its structure transition from the monoclinic phase to the tetragonal phase in W-doped VO 2 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 VO 2 . In addition, W-doped VO 2 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 VO 2 powders are used to prepare thermochromic films, where 1.0 at.% W-doped VO 2 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 VO 2 .