THRESHOLD OF IRREVERSIBLE DOMAIN-WALL MOTION IN SOFT PZT-PIEZOCERAMIC

The nonlinear ac-field dependence of dielectric and piezoelectric coef ficients in soft PZT piezoceramics is studied at f=100 Hz. We demonstr ate that two different thresholds for the onset of nonlinearity exist at E(c2)approximate to 1 V/cm and E(c1)approximate to 100 V/cm, respec tively. At weak fields, the ac-field dependence of the effective diele ctric coefficients obeys a scaling law x=x(0)+A[(E-E-c)/E-c](phi) with the effective coefficient phi=1.5+/-0.1. Above the large held thresho ld, both dielectric and piezoelectric coefficients exhibit a non-analy tic scaling behavior. The nonlinearity is here anisotropic which is re flected by exponents phi=1.0+/-0.1 and phi=1.2+/-0.1 for fields parall el and perpendicular to the poling direction of the ceramic, respectiv ely. The nonlinear domain wall response at fields well below the elect rical depoling held is apparently dominated by the depinning of domain walls rather than by the anharmonicity of the potential energy of the wall.