Infrared modulation via near-room-temperature phase transitions of vanadium oxides & core–shell composites

Abstract

Vanadium oxides (VO_x) are highly promising materials for heat retardant coatings, enabled by their insulator-to-metal phase transition (IMT). Currently, this IMT typically occurs at 68 °C, well above room temperature. Here, we develop a dopant-free approach to lower the IMT temperature to ∼40 °C enabling near-room temperature infrared modulation, by simple, solution phase synthesis. This is achieved by both controlling the stoichiometry of the metal oxide and by using a SiO₂ shell around the VO_x particles, with the difference in thermal expansion coefficient between SiO₂ and VO_x inducing sufficient strain in the VO_x to dramatically lower the IMT temperature. This approach enables the production of a functional solution of suspended VO_x nanoparticles with near-room temperature IMT. The combination of near-room temperature IMT and solution phase nanoparticles dramatically increases the ease, scalability, and efficacy of VO_x application.