Anisotropy of piezoelectricity near morphotropic phase boundary in perovskite-type oxide ferroelectrics

Angle dependence of the piezoelectric displacement along the driving electric field was calculated near the morphotropic phase boundary in the perovskite-type oxide family on the basis of the Landau-Devonshire type free energy function. It was found that the piezoelectric displacement in the tetragonal phase near the morphotropic phase boundary takes a maximum when the field is applied along the [111] direction, while the piezoelectric displacement in the rhombohedral phase takes a maximum in the direction, which depends on the values of the elastic and electrostrictive constants. In both phases the piezoelectric displacements are strongly enhanced near the morphotropic phase boundary.