ORDER-DISORDER TYPE ASPECTS IN DISPLACIVE TYPE FERROELECTRIC PHASE-TRANSITIONS

The self-consistent phonon theory on displacive type phase transitions is reviewed from a new standpoint making use of the analogy to the Moriya theory on itinerant electron ferromagnets. It is shown that order-disorder type aspects observed in displacive type ferroelectrics are naturally included in this theory contrary to the quasi-harmonic theory. The Rhodes-Wohlfarth plot for ferroelectrics of this type is presented, and discussed in association with these aspects.