Effect of the heating rate on crystallization and densification of TiO₂ films prepared from alkoxide solutions containing various organic additives

The effect of the heating rate on crystallization and densification of sol–gel-derived TiO₂ films has been investigated. The TiO₂ gel films were prepared from Ti(OC₃H₇ⁱ)₄ solutions containing alcohols (2-butanol and 2-methoxyethanol), glycols (propylene glycol, diethylene glycol and dipropylene glycol) and chelating agents (acetylacetone and benzoylacetone) as organic additives, followed by heat treatment to 800°C at various heating rates. In the cases without organic additives and with alcohols, anatase films were obtained irrespective of the heating rate, where the refractive indexes of the films were higher for slower heating rate. Conversely, for the films prepared with glycols and chelating agents, rapid heating activated crystallization and densification. In particular, addition of chelating agents led to the formation of rutile films with much higher refractive indexes than those of the anatase films.