Effect of Grain Size on Flexoelectricity

摘要

The grain-size effect of permittivity has been widely studied and its phenomenological theory is well established. In this work, we use such grain-size-effect theory to examine the grain-size effect of flexo-electricity, which has been overlooked so far. Two typical flexoelectric materials are employed, namely, ferroelectric BaTiO3 ceramics and paraelectric SrTiO3 ceramics. The results suggest that the variation of the intrinsic flexoelectric coefficient is completely synchronized with the variation of the grain-size -dependent permittivity for SrTiO3 ceramics. However, this synchronization is overturned in BaTiO3 ceramics, the flexoelectric coefficient of which increases with the grain size rather than dielectric per-mittivity. Under a flexoelectric field, it is proven that the polarization deflection of the 180 degrees domains (more likely to exist for large grain sizes) dominates the flexoelectricity of ferroelectric BaTiO3 ceramics. The observed flexoelectric grain-size effect is beneficial for the design of bulk materials with a high flex-oelectric coefficient and provides a simple and effective way to improve the performance of actuators and sensors based on bulk flexoelectricity.

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