Strong grain size effect on flexoelectric response of Ba0.67Sr0.33TiO3 ceramics

The influence of the grain size on the dielectric and piezoelectric properties of ceramics has been extensively studied, but its impact on the flexoelectricity remains largely unexplored, particularly for Ba0.67Sr0.33TiO3 (BST) ceramics, which are known to exhibit the highest flexoelectric coefficient at room temperature. In this work, BST ceramics with grain sizes ranging from 1.92 to 28.21 μm were prepared using the conventional solid-state sintering method. With increasing grain size, the dielectric constant ɛ increased from 6321.26 to 16276.36, and the flexoelectric coefficient μ12 increased remarkably from 1.09 to 93.51 μC/m. A linear relationship was observed between the flexoelectric coefficient and the dielectric constant, with a nonzero μ12–ɛ intercept. The flexoelectric coefficient μ12 reached its maximum at the Curie temperature and gradually decreased with further increase in temperature. Moreover, BST ceramics with larger grain sizes exhibited reduced relaxor characteristics, with a smaller phase transition diffuseness parameter γ. The significant variation of nearly two orders of magnitude in the flexoelectric coefficient of BST ceramics with different grain sizes may be attributed to the shifting of the phase transition and a higher proportion of mobile domain walls in ceramics with larger grain sizes. Our work provides a reference for the microstructural control of flexoelectric properties in ceramics.