Microscopic origin and relevant grain size effect of discontinuous grain growth in BaTiO3-based ferroelectric ceramics

Barium titanate [BaTiO3 (BT)]-based ceramics are typical ferroelectric materials. Here, the discontinuous grain growth (DGG) and relevant grain size effect are deeply studied. An obvious DGG phenomenon is observed in a paradigmatic Zr4+-doped BT-based ceramic, with grains growing from ∼2.2–6.6 to ∼121.8–198.4 μm discontinuously near 1320 ℃. It is found that fine grains can get together and grow into large ones with liquid phase surrounding them above eutectic temperature. Then the grain boundary density (Dg) is quantitatively studied and shows a first-order reciprocal relationship with grain size, and the grain size effect is dependent on Dg. Fine grains lead to high Dg, and then cause fine domains and pseudocubic-like phase structure because of the interrupted long-range ferroelectric orders by grain boundary. High Dg also causes the diffusion phase transition and low Curie dielectric peak due to the distribution of phase transition temperature induced by internal stress. Local domain switching experiments reveal that the polarization orientation is more difficult near the grain boundary, implying that the grain boundary inhibition dominates the process of polarization orientation in fine-grain ceramics, which leads to low polarization but a high coercive field. However, large-grain ceramics exhibit easy domain switching and high & similar ferroelectricity. This work reveals that the grain boundary effect dominates the grain size effect in fine-grain ceramics, and expands current knowledge on DGG and grain size effect in polycrystalline materials.