Effect of the amount of H2O and HNO3 in Ti(OC3H7i)4 solutions on the crystallization of sol-gel-derived TiO2 films

Titania (TiO2) films were prepared from Ti(OC3H7i)(4) solutions of molar compositions, Ti(OC3H7i)(4): H2O: HNO3: C2H5OH = 1: x: y: 10 (x = 1.0-8.0, y = 0.1-2.0), and the influence of the amount of H2O and HNO3 on the crystallization of the films during the heat treatment was investigated. The precipitation in the coating solutions containing a large amount of H2O over x = 4.0 was suppressed with increasing HNO3 contents over y = 1.0, where the H2O contents in the solutions was able to be changed in the range of x = 1.0-8.0. The increase in the H2O contents led to the increase in the degree of crystallization, crystallite size and reflective index of the resultant TiO2 films, while it decreased the size of the grains that were observed in the scanning electron microscope images. Anatase films with a higher refractive index of ca. 2.25 was obtained at x = 8.0 and y = 1.0-2.0.