Microstructural evolution and overall response of an initially isotropic ferroelectric polycrystal under an applied electric field

Based on the mechanism of domain switch in the constituent grains, a two-level micromechanical model is developed to study the microstructural evolution and nonlinear response of an initially isotropic, fully poled ferroelectric polycrystal under application of an electric field. First the reorientation process of ferroelectric domain in each crystallite is described by a kinetic equation and, with it and a dual-phase theory, its effective electromechanical moduli and polarization fields are determined. The overall response of the ferroelectric ceramic is then calculated self-consistently from the orientational average of its constituent grains. The developed theory is applied to a PLZT polycrystal with rhombohedral grains under an axial electric field. The calculated results provide significant insights into the heterogeneous evolution of new domain concentrations among the constituent grains, and illustrate how the initially isotropic polycrystal evolves into a transversely isotropic one. The changes of piezoelectric constant and dielectric permittivity of the polycrystal as the electric field increases are displayed, and the obtained overall electric displacement versus electric field (D versus E) and strain versus electric field (ε versus E) relations are found to be in general agreement with experimental observations.