Microscopic model of ferroelectric soft modes

Abstract

A diatomic linear chain with non-linear polarizability in one sublattice is studied as a simplified version of a recent microscopic model for ferroelectric soft modes. The dispersion curves are described in a self-consistent approximation for all temperatures of the paraelectric regime. In three dimensions and for T≥T the model yields ω² _F ∞ (T-T_c) for the ferroelectric frequency whereas for T^c>T_c ω² _F tends to the rigid-ion value. The quantum limit (T_c→0) and the ferroelectric regime (T < T_c) are discussed.