Orientational Phase Transition and Dynamic Susceptibility of Hindered-Rotating Dipolar System ---A Librator-Rotator Model---

Abstract

A microscopic theory is presented to study the two-directional orientational phase transition of the interacting dipolar system and its dynamic susceptibility in the paraelectric phase. On the basis of a classical mechanical model that the librational and the rotational motion for a dipole in the hindered-rotation potential can be treated exactly, the statistical mechanical calculations are carried out in the framework of the molecular field approximation and the linear response theory. In this approximation, several characteristic quantities such as Curie temperature, specific heat, static and dynamic susceptibilities, etc. are all obtained rigorously. The present model recovers the dynamics proper to the dipolar motion in the studies of the orientational phase transition and its dynamic susceptibility, so that it offers an approach different from the conventional pseudo-Ising spin model.