Crystallization and densification of alkoxide-derived titania films: Effect of the amount of H₂O in the precursor solutions

Sol–gel derived TiO2 films were prepared from the solutions containing Ti(OC3H7i)4, H2O, HNO3 and C2H5OH by dip-coating, and the effects of the processing parameters (the heat-treatment temperature and time, and the H2O contents in the coating solutions) on the crystallization and densification of TiO2 films during the heat treatment in air were discussed. Anatase films were obtained by the heat treatments over 400 °C, and the increase in heat-treatment temperature and time led to a decrease in film thickness and an increase in grain size, crystallite size and refractive index of the films. Moreover, the crystal growth and grain growth were promoted with increasing H2O content in the coating solutions during the heat treatments over 500 °C, while the crystallization and densification were suppressed by the slow condensation of Ti–OH species below 400 °C at larger H2O contents.