Preparation, electrical and optical properties of (Pb,Ca)TiO3 thin films using a modified sol-gel technique

Calcium modified lead titanate sol was synthesized using lead acetate trihydrate, calcium nitrate tetrahydrate and titanium tetra-a-butoxide as starring materials, methanol and ethanolamine were selected as solvent and stabilizing or complexing agent, respectively. (Pb0.76Ca0.24)-TiO3 thin films were prepared on platinum-coated silicon and fused silica substrates with the solution using the spinning method. The surface morphology and crystal structure, surface compositions and chemical states, electrical and optical properties of the thin films were investigated. The films have good composition homogeneity and thickness uniformity. The dielectric constant and dissipation factor of 1 kHz at room temperature were found to be 280 and 0.027, respectively, for thin films with 0.5 mu m thickness annealed at 600 degrees C for 1 h. The remanent polarization and coervive field were 15 mu C/cm(2) and 64 kV/cm, respectively. The thin films exhibited good optical transmissitivity, and had optical direct transitions. The dispersion relation of refractive index and wavelength followed the single electron oscillation model. The band gap of the him which annealed at 650 degrees C was 3.68 eV. The results also confirmed that ethanolamine was very effective in preparing uniform and dense oxide films, owing to the superior stability of the sols during hydrolytic polycondensation. (C) 1999 Elsevier Science S.A. All rights reserved.