Core-rim structure evolution and electric properties of Ca-Mg-Dy-co-doped BaTiO3 ceramics

The core-rim structure is the micro-basis of BaTiO3-based MLCC dielectric materials. Its formation and evolution mechanism and the effect on electric properties deserve a closer and more detailed study. Herein, a series of core-rim structured 95BaTiO(3)-2CaO-2MgO-1Dy(2)O(3) ceramics were prepared by controlling their sintering time from 3 min to 20 min to record the microstructure evolution process. The EDS line scanning showed a sharp dopant composition gradient between the core and rim, demonstrating the epitaxial formation mechanism of core-rim structured grain. Based on it, systematic microstructure evolution analyses of the morphology, composition, and defects during the sintering were applied and a multi-scale evolution mechanism was put forward. The sintering process was divided into three major stages involving reaction and nucleation, rapid densification, and rapid grain growth. The core-rim structured grains emerged from the first stage and were destroyed in the third stage. Dense ceramics (similar to 96.5%) with core-rim structured grains were obtained in the second stage by limiting the holding times to 5 min. The epsilon '-T spectra and electric strength showed coherent changes and revealed the significant effect of the microstructure feature on the electric properties.