MODEL FOR SWITCHING IN FINITE FERROELECTRIC MEDIA AS A LANDAU PHASE TRANSITION AND COMPARISON WITH EXPERIMENT BY

ABSTRACT A detailed analysis of polarization reversal in ferroelectrics has been performed, in the framework of Landau model for phase transitions. Some important characteristics of homogenous switching have been emphasised and later used in the more general case of inhomogenous switching. The extremes of switching current correspond to the inflexion points of the dielectric hysteresis loop. Hysteresis loops of poled ferroelectric samples are expected to include negative susceptibility regions, for small amplitudes of applied electric field. Two corrections are proposed, in order to improve the agreement between model predictions and experiments. The switching current minimum is removed by the experimental method used for recording the switching responses. Equivalent Landau coefficients and electric field have been defined, in order to integrate the size effects and inhomogenity contribution to switching. We correlated the size effects on critical parameters of switching (coercive field) and ferroelectric to paraelectric phase transition (Curie temperature). The equivalent quantities computed from the model are similar with those obtained from the switching curves of four Barium Titanate ceramic samples having different grain sizes