Effect of ligands on crystal structures and optical properties of TiO2 prepared by sol-gel processes

The refractive index and crystal structures of TiO2 films formed on soda lime glass substrates by sol-gel processes with and without organic ligands were investigated to establish the effect of the ligands on the optical property and crystal structure. The TiO2 prepared with 2-(2-methoxyethoxy)ethanol (MEE) Ligand crystallized to anatase at firing temperatures between 350 and 400 degrees C. The film with 2-methyl-2,4-pentanediol (MPD) ligand, however, crystallized between 400 and 500 degrees C. The refractive indices of the films with MEE were the highest among the three types of films at all the firing temperatures, but those of the films with MPD were the lowest. The MEE ligand aggregates grains of titania gels and accelerates the crystallization of the film, resulting in the densest film and the highest refractive index. The MPD ligand, however, does not aggregates the titania grains and is still present up to high firing temperature of 500 degrees C, resulting in the lowest refractive index. In this sol-gel process, the MEE acts as a kind of a binder in ceramics extrusion processes. (C) 1999 Elsevier Science S.A, All rights reserved.