Low-temperature perovskite-type cadmium titanate thin films derived from a simple particulate sol-gel process

Low-temperature perovskite-type cadmium titanate (CdTiO₃) with a nanocrystalline and mesoporous structure was prepared at various Ti:Cd molar ratios by a straightforward particulate sol-gel route. The prepared sols had a narrow particle size distribution, in the range 23-26 nm. X-ray diffraction and Fourier transform infrared spectroscopy revealed that the powders contained a mixture of ilmenite-CdTiO₃, perovskite-CdTiO₃, anatase and rutile phases, depending on the annealing temperature and the Ti:Cd molar ratio. Perovskite-CdTiO₃ was the major type obtained from cadmium-prominent powders at low temperature, whereas ilmenite-CdTiO₃ was the major type obtained from titanium-prominent powders at high temperature. It was observed that the anatase-to-rutile phase transformation accelerated with decreasing Ti:Cd molar ratio. Furthermore, the ilmenite-to-perovskite phase transformation accelerated with a decrease in both the Ti:Cd molar ratio and the annealing temperature. The crystallite sizes of the ilmenite- and perovskite-CdTiO₃ phases reduced with increasing the Ti:Cd molar ratio. Field emission scanning electron microscopic analysis revealed that the average grain size of the thin films decreased with an increase in the Ti:Cd molar ratio. Moreover, atomic force microscope images showed that CdTiO₃ thin films had a columnar-like morphology. Based on Brunauer-Emmett-Taylor analysis, cadmium titanate powder containing Ti:Cd = 75:25 showed the greatest surface area and roughness and the smallest pore size among all the powders annealed at 500 °C. This is one of the smallest crystallite sizes and largest surface areas reported in the literature, and can be used in many applications in areas from optical electronics to gas sensors.