Thermochromic V1-xWxO2 thin films prepared by wet coating using polyvanadate solutions

Metallic vanadium powder was dissolved in a hydrogen peroxide solution, yielding a hydrosol based on a polyvanadate. A polycrystalline thin film of VO2 was fabricated on a fused silica substrate by spin-coating using this hydrosol followed by reduction in hydrogen and additional post-annealing in a nitrogen atmosphere. The thin film showed a sharp semiconductor-to-metal transition and concomitant thermochromic switching at 67 degrees C. Tungsten-doped thin films (V1-xWxO2) were easily fabricated by a similar technique. The transition temperature of a doped film with x = 0.015 was as low as 36 degrees C.