PHENOMENOLOGICAL THEORY OF ANTIFERROELECTRIC TRANSITION .I. SECOND-ORDER TRANSITION

Kittel's free energy expression as normalized to involve only dimensionless variables, and manipulated to explain behaviors of second-order linear antiferroelectrics. It is a function of polar and antipolar variables, each of which are proportional to sum and difference of polarizations of two sublattices respectively, and it contains dimensionless temperature and external field as parameters. Free energy maps as functions of the two variables were computed at various values of two parameters. They visualize stability of states and how induced transition occurs under the external field. Stabilities of states were examined analytically, and restrictions on the two parameters for stability were obtained. Below the transition point antiferroelectric state is always more stable than polar state. Under external field, the well-known double hysteresis loop was explained satisfactorily considering stability of the state on two branches of polarization vs. field. Critical field for induced transition was also calculated as a function of temperature. Relation between susceptibility and temperature showed new behaviors under bias field. Discontinuous change in susceptibility is revealed at the transition point, and susceptibility goes to infinity at a certain temperature and bias field. © 1969, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.