Strain-gradient-induced electric polarization in lead zirconate titanate ceramics

Strain-gradient-induced polarization or flexoelectricity was investigated in unpoled soft lead zirconate titanate (PZT) ceramic where the texture symmetry m∞∞ forbids macropiezoelectricity. Even under high strain gradient (1 m−1) the induced polarization is small (1.6 μC/m2) at 20 °C. Higher strain gradients induce ferroelastic poling and an additional extrinsic contribution to the flexoelectric coefficient μ12 raising the value from 0.5 to 2.0 μC/m. Cooling through the Curie point (TC) under maximum stress (80 MPa) where the peak permittivity (∼20 000) could raise μ12 to 20 μC/m, the equivalent electric field is still only ∼1 kV/m, inadequate to achieve significant ferroelectric poling. The situation may be different in thin PZT films where much larger strain gradients can occur.