The grain-size-dependent behaviors of nano-grained ferroelectric polycrystals: A phase-field study

In this work, the electromechanical behaviors of nano-grained ferroelectric ceramics are numerically studied with different grain sizes. The material under investigation is nano-grained barium titanate ceramic, which shows noticeable grain size dependence of the electromechanical characteristics. A 2D polycrystal phase-field model is developed to investigate the hysteresis loops and the process of the microstructural evolution upon applied bipolar electric field. A core-shell model has been selected to treat the grain interior and the grain boundary with separate ferroelectric properties. Such treatment is analogous to the consideration of a grain-boundary-affected zone as in the study of nano-crystalline plasticity. The grain size dependence of the ferroelectric properties, e.g.; coercive electric field and remnant polarization, is examined based on this model, and the mechanism of the grain size dependence is analyzed.