Optical and electrical properties of vanadium oxides synthesized from alkoxides

Vanadium oxides have been synthesized via the hydrolysis and condensation of vanadium alkoxides VO(OR)(3). Different materials are actually obtained depending on the hydrolysis ratio h = H2O/V. Spin-coated alkoxides lead to vanadium dioxide. These thermochromic VO2 thin films exhibit a metal-insulating transition. They are transparent at room temperature and IR reflecting above 70 degrees C. The transition temperature can be easily modified by doping with other metal cations. Amorphous ore-polymers are formed via the partial hydrolysis of vanadium alkoxides. They give optically transparent thin films that could be used in electrochromic display devices. The hydrolysis of vanadium alkoxide in the presence of an excess of water leads to ribbon-like particles of hydrated oxide V2O5. nH(2)O. Mesophases are observed in vanadium oxide gels and sols that exhibit a nematic liquid crystal behavior. They can even be oriented by applying a magnetic field. Anisotropic thick films can be deposited from these gels. They exhibit a strong preferred orientation. Mixed proton and electron conduction is observed in these gels that can be used as reversible cathodes for lithium batteries. (C) 1999 Elsevier Science S.A. All rights reserved.