Influence of calcination temperature on structural and optical properties of TiO2 thin films prepared by sol–gel dip coating

TiO2 thin films were prepared by sol–gel dip coating and their structural and optical properties were examined at various calcination temperatures. The X-ray diffraction (XRD) results showed that TiO2 thin film calcined at 300 °C was amorphous, and transformed into the anatase phase at 400 °C, and further into rutile phase at 1000 °C. The phase transformation temperature has been dependent upon the concentration of catalyst HCl. The crystallite size of TiO2 thin films was increased with increasing calcination temperature. The micro-particles in the films grew by intra-agglomerate densification below 1000 °C, whereas they grew by inter-agglomerate densification above 1000 °C. The transmittance of the films calcined at 1000 and 1100 °C was reduced significantly in the wavelength range of about 300–700 nm due to the change of crystallite phase and composition in the films. The refractive index of TiO2 thin films was increased with increasing calcination temperature, and the film thickness and the porosity of TiO2 thin films were decreased.