Investigation On The Microstructure And Dielectric Relaxation Behavior Of Bi-based Pyrochlore Ceramics

Taken Materials Science as the viewpoint and the relationship of structures and properties the springboards, groups of Bi-based pyrochlore materials were prepared by conventional solid-state reaction methods. Annealing processing was applied to verify the micro-defects information of series ceramics. The defects information and dielectric relaxation properties had been studied. The detailed microstructure information related to the dielectric relaxation of materials had been summarized. The influence of chemical composition on the microstructure and dielectric properties of pyrochlores materials had been investigated. We have got some conclusion as following:The effect of B site substitution on dielectric properties of BZMN ceramics was investigated. It is discovered that a shift of the relaxation peak for the dielectric properties is obviously observed. The difference in the temperature peaks of dielectric relaxation and the parameters of dielectric relaxation was analyzed: The increasing of B site ion radius causes strong correlation among highly polarizable octahedrals. The valence of B site ion may change easily in reducing atmosphere, which raises the conductivities of the material.The dielectric relaxation properties of (Bi_1.5Zn_0.5-xSr_x)(Ti_1.5Nb_0.5)O₇ (BZSTN, x=0⁰.5) ceramics had been studied, It is discovered that a shift of the relaxation peak for theεis obviously observed, When x increases samples, A shift of the relaxation peak to high temperature was indicate These provide a experimental basis for further exploration of dielectric relaxation,mechanism:A defect dipole model can explain the phenomenon relaxation in low temperature; ionic polarization model can explain the phenomenon relaxation in high temperature. The dielectric relaxation properties of (Bi_1.5Zn_0.5-xLi_x)(Ti_1.5Nb_0.5)O_7-xF_x ( BZTN-LiF, x=0⁰.5) ceramics had been studied. When x increases a shift of the relaxation peak for the dielectric loss is obviously observed, a shift of the relaxation peak to high temperature was caused by activation energy increasing or the interaction energy increasing.Debye model, V-F relationship, New glass model Curie-Wiss's law and Barrett Equation were used to analysis the property of dielectric relaxation, which can explain the relationship between microstructure and dielectric properties of pyrochlores materials.Thermal annealing is a good way to improve the dielectric properties of Cubic Bi-based pyrochlores, and this effect can be attributed to the decrease of grain boundary. The experimental results revealed after annealing in oxygen ambient, the oxygen vacancies were largly reduced, the stress between boundaries is largly decrease, therefore a decrease of relaxation and an improvement of dielectric properties ware observed in the oxygen annealing samples.