Domain switching and shear-mode piezoelectric response induced by cross-poling in polycrystalline ferroelectrics

The mechanisms contributing to the electromechanical response of piezoelectric ceramics in the shear mode have been investigated using high-energy synchrotron x-ray diffraction. Soft lead zirconate titanate ceramic specimens were subjected to an electric field in the range 0.2–3.0 MV m−1, perpendicular to that of the initial poling direction, while XRD patterns were recorded in transmission. At low electric field levels, the axial strains remained close to zero, but a significant shear strain occurred due to the reversible shear-mode piezoelectric coefficient. Both the axial and shear strains increased substantially at higher field levels due to irreversible ferroelectric domain switching. Eventually, the shear strain decreased again as the average remanent polarization became oriented toward the electric field direction. The lattice strain and domain orientation distributions follow the form of the total strain tensor, enabling the domain switching processes to be monitored by the rotation of the principal strain axis. Reorientation of this axis toward the electric field direction occurred progressively above 0.6 MV m−1, while the angle of rotation increased from 0° to approximately 80° at the maximum field of 3.0 MV m−1. A strong correlation was established between the effective strains associated with different crystallographic directions, which was attributed to the effects of elastic coupling between grains in the polycrystal.