OPTICAL-PROPERTIES OF SOL-GEL DERIVED VANADIUM-OXIDE FILMS

Vanadium oxide gels can be made from vanadate aqueous solutions or fro m vanadium alkoxides. The condensation of vanadic acid gives long ribb on-like oxide particles which macroscopically orient in the same direc tion in aqueous sols when their concentration is larger than 0.12 mol . l(-1). These anisotropic sols and gels should be considered as lyotr opic nematic liquid crystals. Thick films in which ribbons align along the same direction can be deposited. These oriented coatings exhibit improved electrochemical properties as reversible cathodes for lithium batteries. Amorphous ore-polymers are formed via the controlled hydro lysis of vanadium alkoxides. They allow the deposition of optically tr ansparent thin films that exhibit interesting electrochromic propertie s and turn reversibly from yellow to green upon electrochemical reduct ion. Moreover these alkoxide derived films can be easily reduced into vanadium dioxide. These VO2 thin films exhibit thermochromic propertie s and could be used as optical switches in the infrared. The transitio n temperature of these VO2 films can be modified by doping the vanadiu m oxide with other cations.