Threshold of irreversible domain wall motion in soft PZT-piezoceramic

The nonlinear ac-field dependence of dielectric and piezoelectric coefficients in soft PZT piezoceramics is studied at f = 100 Hz. We demonstrate that two different thresholds for the onset of nonlinearity exist at E_c2≈1 V/cm and E_c1≈100 V/cm, respectively. At weak fields, the ac-field dependence of the effective dielectric coefficients obeys a scaling law x = x₀+A[(E-E_c)/E_c]^φ with the effective coefficient φ = 1.5±0.1. Above the large field threshold, both dielectric and piezoelectric coefficients exhibit a non-analytic scaling behavior. The nonlinearity is here anisotropic which is reflected by exponents φ = 1.0±0.1 and φ = 1.2±0.1 for fields parallel and perpendicular to the poling direction of the ceramic, respectively. The nonlinear domain wall response at fields well below the electrical depoling field is apparently dominated by the depinning of domain walls rather than by the anharmonicity of the potential energy of the wall.