Variation of structural and optical properties of sol-gel TiO 2 thin films with catalyst concentration and calcination temperature

Abstract

TiO 2 thin films were prepared on quartz glass by sol-gel process and their structural and optical properties were examined at various catalyst concentrations and calcination temperatures. The as-deposited TiO 2 thin films are amorphous, and they transform into the anatase phase at 400–600 °C, and into the anatase–rutile phase at 800 °C, and further into the rutile phase at 1000 °C. The temperature of phase transformation is decreased with the concentration of catalyst HCl. The crystallite size of TiO 2 thin films is increased with increasing calcination temperature and catalyst concentration. The secondary particles in the TiO 2 thin films grow by intra-agglomerate densification below 800 °C, whereas they grow by inter-agglomerate densification above 800 °C. The deposited TiO 2 thin films have high transparency in the visible range. The transmittance of the films calcined at 800 and 1000 °C are significantly reduced in the wavelength range of 300–800 nm due to the change of crystallite phase and increased particle size. The refractive index of TiO 2 thin films is increased with increasing calcination temperature and catalyst concentration. On the other hand, the porosity of TiO 2 thin film is decreased.