Nonlinear ferroelectric domain wall response

The ac-field dependence of complex dielectric coeffcients in the improper ferroelectric phase of incommensurate Rb₂ZnCl₄ crystals is analyzed and compared with those observed in donor doped lead zirconate titanate (PZT) piezoceramics. For all coefficients examined, a threshold field for the onset of nonlinearity exists leading to qualitatively the same non-analytic scaling behavior above threshold. Due to the similar nonlinear behavior of very different ferroelectric systems, we suggest that a universal mechanism may exist in a larger class of ferroelectrics causing nonlinearity at moderate field level. This may be related to the dynamics of randomly pinned elastic interfaces driven at field strengths slightly above threshold for collective interface motion.