Two Different Mechanisms of the Curie-Weiss Dielectric Susceptibility in Ferroelectrics

Abstract

The Curie-Weiss law of the dielectric susceptibility χ in ferroelectrics is shown to be derived from two different mechanisms in the self-consistent phonon approximation: One is the increase in the correlation between dipoles which is related to the magnitude of the electrostatic interaction D. The other is the decrease in the mean square amplitude of the soft mode, which leads to the Curie-Weiss law through the rate of increase 1⁄t₀ of an individual susceptibility with the decreasing effective “dipole moment”. The dependence of χ on temperature has been numerically computed to investigate the dependence of the Curie constant on t₀ and D. The ratios of the paraelectric moment to the saturation moment have been evaluated from available experimental data in ferroelectrics. Deviations of these ratios from unity in displacive type ferroelectrics are explained in terms of t₀.