Relaxation Process in Ferroelectrics near the Curie Temperature

Abstract

A phenomenological approach is given to the problem of the relaxation process in ferroelectrics near the Curie temperature. It is shown that most of anomalous dielectric behaviours of order-disorder type ferroelectrics can be understood by assuming a distribution of relaxation times and their critical slowing down. A more microscopic approach to the same problem is also made for a specific model of KD₂PO₄ which is regarded as a kind of Ising spin system with two kinds of nearest neighbour interactions. Dynamical properties of this system are investigated on the basis of the Glauber's equation. In actual calculation, a time-dependent cluster approximation is employed. The system is shown to exhibit a relaxation process with two relaxation times, one tending to infinity as the Curie point is approached, the other being almost constant through the paraelectric phase.