Structural and Electrical Properties of Sol-Gel-processed CdTiO₃ Powders and Films

Cadmium titanate, CdTiO₃, was prepared by the sol-gel technique in bulk and in thin film form. The thermal evolution of the gels and the phase changes were studied by thermogravimetric analysis (TGA), X-ray diffractometry (XRD) and Raman and energy-dispersive (EDS) speetroscopies. The morphology of the samples was observed using scanning electron microscopy (SEM). Gels heated to 800°C gave rise to powders with only the ilmenite-like phase. The orthorhombic perovskite phase is the only crystalline phase observed after a 4 h heat-treatment at 1100°C. With respect to the conventional preparation method by solid-state reaction, by the sol-gel method it is possible to prepare the ilmenite phase at lower temperatures and the perovskite phase in a shorter time. Clear, homogeneous thin films were obtained by the dip-coating method. The refraction index and the thickness of the films were measured using ellipsometry. The humidity-sensitive electrical properties were measured for thin films deposited on alumina substrates with comb-type gold electrodes, heated to 200°C and 450°C. The films heated to 200°C, which still contained organics, showed a variation of the resistance of six orders of magnitude in the relative humidity (RH) range tested (4-87% RH). The films heated to 450°C, made of ilmenite-type CdTiO₃, were nearly insensitive to RH.