Processing and characterisation of sol-gel glasses and powders in the system TeO₂-TiO₂

Sol-gel processing routes have been developed for the production of thin films and powders in the system TeO₂-TiO₂ from tellurium and titanium alkoxides. The structure and properties of the resultant materials have been characterized as a function of heat treatment temperature. Pure sol-gel derived TeO₂ thin films are difficult to prepare with good optical transparency due to the presence of organic impurities and/or a highly dispersed metallic tellurium phase when heated at temperatures up to approximately 340°C, with crystallization to α-TeO₂ occurring when the heat treatment temperature is further increased. Additions of TiO₂ were found to retard the crystallisation of the α-TeO₂ but promote the formation of other TiO₂ or TiTe₃O₈ phases. However, an optimum composition in the range 0.9TeO₂ 0.1TiO₂ was identified, which allows optically transparent thin films to be prepared with high refractive index and offers the potential for practical device manufacture.