Stress Effect On PZT Films And Substituent Effect On CCTO Ceramic

Ferroelectric films have recently received considerable attention due to their applications in the dynamic random access memoriy, optoelectronic devices, and novolatile memories, etc. In this dissertation, the modified Landau-Devonshire thermodynamic theory has been used to investigate the ferroelectricity of Pb(Zr_0.7, Ti_0.3)O₃ film grown on MgO substrate. A set of gradient thermal stresses are imposed on the films. The stress-temperature diagram, the spontaneous polarization and the dielectric susceptibility at 25℃on the stress were computed. Structure transitions of first order could be driven by the stress. The mean of out-plane spontaneous polarization and dielectric susceptibility on the temperature were also predicted.BaCu₃Ti₄O₁₂ (BCTO) ceramics revealed a high dielectric constant of 104 and was found to be constant between 100 and 600K. However, its dielectric constant displayed 100-fold reduction below 100K without any detectable change of crystallographic structure. The reason is not clear now. BaCu₃Ti₄O₁₂ (BCTO) ceramics were prepared by the traditional solid-state reaction technique and calcined at 950℃, and sintered at different temperature. The temperature dependence of dielectric constant and dielectric loss at different frequencies of each sample were measured. The dielectric constant of BCTO was smaller than CCTO's. Tolerance factor analysis found that the crystal structure of BCTO easily distorted. XRD showed that the samples not only contained BCTO phase, but also impurities such as Cu₃TiO₅ and Cu₃TiO₄.