Ferroelectric domains and polar clusters in disordered structures

Abstract

Known experimental facts concerning ferroelectric phase transitions in disordered clusters are discussed in terms of phenomenological kinetik theory.¹ Depending on the values of several parameters, one of the following three alternatives may be observed. a) Randomly oriented nanoclusters of the ferroelectric short-range order make their appearance in paraelectric matrix in a wide temperature range. Under cooling the size of the clusters grows slightly and the low-temperature state remains macroscopically isotropic. Such behavior is typical of relaxor ferroelectrics. b) Normal transition from paraelectric to ferroelectric phase occurs at a certain temperature and macroscopic domains are formed as in the case of ordered structures. c) Under cooling a sharp spontaneous transformation from relaxor state with polar nanoclusters to normal ferroelectric state with macroscopic domains takes place at certain temperature.