Sol-gel synthesis of oxide materials

The sol-gel process is based on the hydrolysis and condensation of molecular precursors. The chemical design of these precursors provide an interesting tool to control condensation reactions and tailor the nanostructure of the oxide materials. The condensation of vanadic acid in aqueous solutions gives lyotropic nematic sols or gels that lead to anisotropic vanadium oxide layers when deposited onto a flat substrate. These oriented layers exhibit improved electrochemical properties as cathode materials. Amorphous oxopolymers are obtained via the controlled hydrolysis of vanadium alkoxides. They can be easily reduced into VO2 thin films that exhibit highly reversible thermochromic behavior. The chemically controlled condensation of zirconium alkoxides leads to stable colloidal solutions of monodispersed zirconia nanoparticles. The mild conditions associated with sol-gel chemistry allow the encapsulation of biomolecules within a silica glass. Even whole cell organisms such as protozoa can be encapsulated. Their cellular organization and antigenic properties are preserved and they can be used for immunoassays. (C) 1998 Acta Metallurgica Inc.