Optical and electrical properties of vanadium oxides synthesized from alkoxides

Vanadium oxides have been synthesized via the hydrolysis and condensation o f vanadium alkoxides VO(OR)(3). Different materials are actually obtained d epending on the hydrolysis ratio h = H2O/V. Spin-coated alkoxides lead to v anadium dioxide. These thermochromic VO2 thin films exhibit a metal-insulat ing transition. They are transparent at room temperature and IR reflecting above 70 degrees C. The transition temperature can be easily modified by do ping with other metal cations. Amorphous ore-polymers are formed via the pa rtial hydrolysis of vanadium alkoxides. They give optically transparent thi n films that could be used in electrochromic display devices. The hydrolysi s of vanadium alkoxide in the presence of an excess of water leads to ribbo n-like particles of hydrated oxide V2O5. nH(2)O. Mesophases are observed in vanadium oxide gels and sols that exhibit a nematic liquid crystal behavio r. They can even be oriented by applying a magnetic field. Anisotropic thic k films can be deposited from these gels. They exhibit a strong preferred o rientation. Mixed proton and electron conduction is observed in these gels that can be used as reversible cathodes for lithium batteries. (C) 1999 Els evier Science S.A. All rights reserved.