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

Abstract

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 95BaTiO₃–2CaO–2MgO–1Dy₂O₃ 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 (∼96.5%) with core–rim structured grains were obtained in the second stage by limiting the holding times to 5 min. The ε′–T spectra and electric strength showed coherent changes and revealed the significant effect of the microstructure feature on the electric properties.