Study On Dielectric Behavior Of BaTiO₃ Ceramics

Barium titanate(BaTiO₃) is a dielectric material, with a perovskite (ABO₃) structure, it is the primary material for high dielectric constant ceramic capacitors due to its excellent electronic performance, such as ferroelectric, piezoelectric, high dielectric constant and positive temperature coefficient effect, etc. And relaxor ferroelectrics based on BaTiO₃ are important dielectric of multilayer ceramics capacitor because of their large permittivity, phase transition temperature and relaxor phase transition behavior. Therefore, for its many applications in electronic devices, the study of relaxor property on BaTiO₃ ceramic has attracted a considerable amount of researchers' interesting.In this thesis, Ba(Ti_0.91Zr_0.09)O₃ ferroelectric ceramics are prepared by a traditional solid phase reaction. Sintering characteristic, phase transition and ferroelectric, piezoelectric properties of Ba(Ti_0.91Zr_0.09)O₃ ceramics doped with additive have been investigated. The main results are as follows:1. Sintering characteristic of Ba(Ti_0.91Zr_0.09)O₃ ceramics are investigated for CuO-BaO mixture addition. The results showed that in spite of pre-calcined or post-calcined Ba(Ti_0.91Zr_0.09)O₃, CuO-BaO additives can lower the sintering temperature, but dielectric relaxor properties is observed at orthorhombic -tetragonal phase transition point for pre-calcined Ba(Ti_0.91iZr_0.09)O₃ with CuO-BaO addition. With increasing of Cu/Ba ratio, orthorhombic-tetragonal and tetragonal-cubic dielectric phase transition peak becomes flat, relaxation phenomenon is obviously observed. The polarization hysteresis loops exhibits a typical relaxor ferroelectric behavior. The research on piezoelectric properties discovers that piezoelectric coefficients increase with increasing grain size.2. The effect of doped with diversity oxide (A-site: Bi₂O₃, Li₂O, B-site: CuO, MoO₃, Al₂O₃) on dielectric property of Ba(Ti_0.91Zr_0.09)O₃ ceramics are investigated. According to charge balance principle, the defects are induced by A-site or B-site heterovalent substitute for Ba(Ti_0.91Zr_0.09)O₃ ceramics. The results show that the samples became relaxor ferroelectric when rather large doping contents. And with the increasing of doping content, the phase transition became more relaxed. The different valence, radius and polarization of heterovalent ion substitution in the material lead to increase disorder and create local-strain. This could be attributed to polar nanoregions which are brought by local-strain.3. The effect of cationic substitution of A and B-site (Bi-Al, Li-Mo) for Ba(Ti_0.91Zr_0.09)O₃ ceramics on dielectric property are investigated. The evolution from a normal ferroelectric to a relaxor ferroelectric is easily observed for A and B-site codoped. The more polar nanoregions induced by A and B-site co-doping, the more easily relaxor property occurred,...