Study On Synthesize And Modification Of BaTiO₃-Bi (Mg_1/2Ti_1/2)O₃ Ceramics With High Temperature Stability Over Wide Range

Multilayer ceramic capacitors (MLCC) are important electric components which are used in almost all areas of electronic field. Barium titanate is a kind of perovskite ferroelectrics with high specific perimittity and long lifetime of insulation resistance, which was the most widely developed and used. However, the Curie point of barium titanate is only 130℃, limiting its maximum operating temperature, unable to meet the higher temperature stability requirements.This paper focused on the structure, the dielectric properties and relaxor phenomena of (1-x)BaTiO3-xBi(Mg1/2Ti1/2)O3 (BT-BMT) system especial for x=0.01-0.06. The studies showed that BMT-modified BT system exhibited significant frequency dispersion and diffused phase transition and depressed, broad dielectric peak. The solubility of BMT into BT is only 7 mol%. According to low Tm, low temperature coefficients of capacitance and good adjustability, nominal composition 0.85BT-0.15BMT was potentially useful for application in XnR type MLCC by doping additives.Nb2O5, CO2O3 doping BT system can enhance the temperature stability effectively. Howeve, different technology caused variety of the ceramics microstructure. This paper focused on the formation mechanism of core-shell microstructure of Nb, Co doped 0.85BT-0.15BMT system. Two processes corresponding to different doped order lead to different microstructure, while both the ceramics meet the X8R requirements with:ε～1000, tanδ< 1.5%, |ΔC/C |≤±15%(-55～155℃).Based on the relations between the core-shell microstructure and dielectric properties, a multi-shell microstructure ceramics was designed and synthesized to widen the working temperature range. This paper analyzed the influence of process on the microstructure and properties. It was showed that the multi-shell structure ceramic can be obtained by sol-gel coating and fine powder mixing method. The dielectric properties of ns:nx=1:8 prepared by approach B is the best, after adjusting the molar ratio of shell/core and sintering parameters (ε～1800, tanδ～2.0%, |ΔC/C |≤±15%(-55～150℃)).