Nonlinear ferroelectric domain wall response

The ac-field dependence of complex dielectric coefficients in the improper ferroelectric phase of incommensurate Rb2ZnCl4 crystals is analyzed and com pared with those observed in donor doped lead zirconate titanate (PZT) piez oceramics. For all coefficients examined, a threshold field for the onset o f nonlinearity exists leading to qualitatively the same non-analytic scalin g behavior above threshold. Due to the similar nonlinear behavior of very d ifferent ferroelectric systems, we suggest that a universal mechanism may e xist in a larger class of ferroelectrics causing nonlinearity at moderate f ield level. This may be related to the dynamics of randomly pinned elastic interfaces driven at field strengths slightly above threshold for collectiv e interface motion.