Electrochemical Synthesis of Amorphous VO₂ Colloids and Their Rapid Thermal Transforming to VO₂ (M) Nanoparticles...

Amorphous VO₂ (a-VO₂ ) colloids were synthesized by electrochemical anodic oxidation of metallic vanadium. It was found that the a-VO₂ colloids have a cotton-like morphology composed of very small clusters, and that the crystallization temperature of the a-VO₂ colloids can be adjusted either by the electrolyte of the anodic oxidation or/and the dispersion agent of the colloids. VO₂ (M) nanoparticles (NPs) (and a NP film) with an average size of about 50 nm can be obtained by a rapid thermal annealing of the a-VO₂ colloids at 310 °C under air, which is beneficial for practical applications. The VO₂ (M) NP film shows an obvious metal-semiconductor transition with a resistance less than 10 Ω in the metallic state. An integral visible transmittance of 40.7 %, a solar transmittance modulation of 9.4 %, and a resistance modulation in the order of 5×10⁴ were realized in the VO₂ (M) NP film.