Coupling effects in ferroelectric superlattice

We consider a model superlattice consisting of two coupling ferroelectric materials within the framework of Landau phenomenological theory. We have studied the effects of the coupling between two sublattices on the polarizations in three different situations of superlattice structures, depending on the choice of the Landau phenomenological coefficients. For a given coupling constant, we also calculate the sublattice polarizations as a function of the film thickness and the temperature.