Mechanism of ferroelectricity in DSP type crystals

Abstract

Dielectric and structural studies of the DSP family (DSP, DDSP and DLP) are reviewed and the mechanism of the ferroelectric phase transition is discussed on the basis of the experimental evidence. It is found, by comparing the experimental results with the Weiss theory, that the electrostatic dipoledipole interaction is not important in the ferroelectric phase transition. Ordering of the methyl groups which bear only a minor part of the dielectric polarization causes the transition from the paraelectric phase to the ferroelectric phase. The ionic atoms, Ca, Sr(Pb) and O, shift their equilibrium positions to produce the major part of the spontaneous polarization. Reorientation of the methyl groups is affected pronouncedly by the ionic atoms.