Relaxor behavior and morphotropic phase boundary in a simple model

A simple model to reproduce the strong enhancement of the dielectric response near the morphotropic phase boundary (MPB) is proposed. This model consists of a long-range dipole-dipole interaction and compositional chemical disorder incorporated by the variation in lengths of dipole moments. By applying a Monte Carlo simulation, we show that a ferroelectric boundary phase appears between an antiferroelectric phase and a relaxor ferroelectric phase at an optimal strength of randomness. In the boundary phase, the ferroelectric domain becomes extremely large and flexible to external electric fields, leading to a huge dielectric response. This observation indicates that the huge dielectric response near the MPB originates from local polarization rotation under the suppression of anisotropy by phase competition.