Effect of grain size on the domain structures and electromechanical responses of ferroelectric polycrystal

The effect of grain size on the domain structures and electromechanical responses of ferroelectric polycrystals is investigated by a phase field model. The phase field simulations show that the different types of domains in different size of grains play an important role in the size-dependent properties of ferroelectric polycrystals. It is found that the remnant polarization, coercive field and dielectric coefficient increase monotonously with the increase of grain size. However, the piezoelectric coefficient increases first and then decreases as the grain size increases. The decrease of vortex domains is responsible for the increase of piezoelectric coefficient in the range of small grain size, the decrease of 90 degrees domain walls results in the decrease of piezoelectric coefficient in the range of large grain size. In addition, different domain structures in different size of grains have also great influence on the mechanical depolarization of the ferroelectric polycrystals subjected to a compressive stress.