Thermochromic V 1-x W x O 2 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 VO 2 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° C. Tungsten-doped thin films ( V 1- x W x O 2 ) were easily fabricated by a similar technique. The transition temperature of a doped film with x =0.015 was as low as 36° C.