Effect of grain boundary on the electromechanical response of ferroelectric polycrystals

Abstract

The effect of grain boundaries on the electromechanical response of a ferroelectric polycrystal subjected to an electric field or stress is investigated numerically by using a phase field model. The grain boundaries in the phase field model are regarded as dielectrics in which the ferroelectric properties are degraded completely. The phase field simulations show that the presence of dielectric grain boundaries results in a large build-in depolarizing field in grains. The depolarizing field has a significant influence on the coercive field, the switching behaviour of ferroelectric domain under an electric field or stress, and the piezoelectric and dielectric properties of the ferroelectric polycrystal. It is found that both coercive field and remnant polarization decrease with the increase of the thickness of dielectric grain boundary. However, the piezoelectric coefficient and permittivity of the ferroelectric polycrystal become larger when the thickness of dielectric grain boundary increases. The enhancement of dielectric and piezoelectric properties by the dielectric grain boundary suggests a new degree of freedom to tune the electromechanical response of ferroelectric polycrystalline materials.

Anomalous toughening in nanoscale ferroelectrics with polarization vortices

“…In the phase-field model of ferroelectric materials, the polarization vector P = (P 1 , P 2 , P 3 ) is taken as the order parameter to describe the free energies of ferroelectric systems. The total free energy of the ferroelectric system F, can be described by [62]:…”

“…dF/dP i (r,t) represents the thermodynamic driving force for the spatial and temporal evolution of the ferroelectric system. Using the variation or principle of virtual work, the weak form (or integral form) of the governing equation can be obtained as [51,62]:…”

Phase-field model simulation of ferroelectric/antiferroelectric materials microstructure evolution under multiphysics loading

“…And the full affection of domain boundary is still to be discovered. Similar but more significant grain boundaries are simulated by Tong-Yi Zhang's group [16], in a real space phase field model, they define that grain boundary to be of finite width and with same mechanical property but dielectric. It is found that the existence of finite width grain boundary introduce a large depolarization energy, increased piezoelectric coefficient and permittivity of polycrystalline ferroelectrics.…”

“…It is found that the existence of finite width grain boundary introduce a large depolarization energy, increased piezoelectric coefficient and permittivity of polycrystalline ferroelectrics. And the increase of grain boundary thickness is related to decreasing of coercive field form the hysteresis loop [16].…”

“…Defect Arrows indicate polarization direction, color denoting value of polarization component P1 [16].…”