  We study theoretically the influence of the underlying domain microstructure
on the electromechanical properties of ferroelectrics. Our calculations are
based on a continuum approach that incorporates the long-range elastic and
electrostatic interactions. The theory is used to simulate the piezoelectric
properties of a two dimensional model ferroelectric crystal. Simulation results
indicate that the electromechanical response of the ferroelectric is strongly
dependent on the domain microsctructure, including domain walls. This is
particularly true for the case when an electric field is applied along a
non-polar direction.

Materials Science