The Dielectric Property And High Temperature Dielectric Relaxation Study On BaTiO₃-based Ferroelectric Ceramics

Barium titanate (BaTiO3) is one of perovsikte ferroelectrics and its Curie temperature is 393 K. Based on the excellent dielectric properties, ferroelectric properties, barium titanate is widely used in many fields of production, not only at the same time, it has always been the hot spot of the ferroelectric materials research. It is well known that the matrix materials doped with other elements or with other substances to form solid solution structure, which can be controlled variables to improve the performance of the matrix material. In this thesis, a series of BaTiO3-based ceramics are synthesized by the traditional solid state reaction method.BaxS1-xTiO3 (BST) is form by the doping of Sr taking place in A site of Barium titanate. We present a systematic study on ferroelectric, dielectric, and dielectric relaxation at high temperature. X-ray diffraction results indicate that all BST samples are tetragonal structure. And the excellent hysteresis loop of samples is measured at room temperature as well. In dielectric studies of BST, a sharp phase transition is exhibited and the Curie temperature increases with increasing Ba content. With the increase of temperature, a dielectric relaxation is observed in high temperature range of 573-823 K. From impedance measurements, the activation energy for relaxation and conduction is calculated as approximately 1 eV, which suggests that relaxation in BaxSr1-xTiO3 ceramics at high temperatures is associated with the short-range hopping of ions caused by oxygen vacancies. After oxygenation treatment, the variation of dielectric behaviors and activation energy verified that the oxygen vacancies are the origin of the dielectric relaxation. The leakage current of BaxSr1-xTiO3 ceramics may be associated with the combined effect of oxygen vacancies and the size of the largest grams.When using equal amount of Bi and Na to dope in Barium titanate, (Bi0.5Na0.5)1-xBaxTiO3 (BNBT) come to being. In the temperature region of BNBT phase transition, a diffuse phase transition peak is exhibited. According to the fitting results of Curie-Weiss law, the phase transition of BNBT ceramics become stronger phase with decreasing Ba content. In the high temperature area, BNBT ceramics show a negative temperature coefficient of resistance behavior and the dielectric relaxation phenomenon. The Arrhenius analyses indicate that the relaxation in BNBT ceramics at high temperatures is associated with the oxygen vacancies.Using Bi as doping elements added to the (Ba0.8Sr0.2)TiO3, then (Ba0.8Sr0.2)1-1.5xBixTiO3 (BSBT) solid solution can be got. The scanning electron microscopy test results show that the grain size of the samples increase firstly and then decrease with the increase of Bi content. The results of dielectric indicate that the dispersion degree of diffuse phase transition of samples also first increased and then decrease. In addition, we suggest that the diffuse dielectric anomaly for all samples is a competition effect between the dielectric relaxation behavior and the various of the relaxation strength. The incremental portion of the diffuse dielectric anomaly is mainly controlled by the variation of the relaxation time and the reducing part is dominantly controlled by the variation of the relaxation strength, which results from the disturbance by the electrical conduction.