Electromechanical Properties of Order-Disorder Type Ferroelectrics. II. Electrostriction

Abstract

The static and dynamic electrostrictive properties of order-disorder type ferroelectrics are discussed. The theory takes into account properly the role of an ionic polarization which interacts with a dipole system. The electrostrictive constants M and Q with which the electrostrictive contribution to the total strain is written as ME² or QP² are calculated. The constant M diverges when T_C is approached from above as well as from below, its sign below T_C being opposite to that above T_C. The constant Q shows a marked temperature dependence in the ferroelectric phase. Besides, it shows a sharp cusp at T_C when the Curie constant is small. The electrostrictive strain under an alternating electric field is expected to show an anomalous phase lag. All these are due to the dielectric nonlinearity and/or the presence of an ionic polarization. When the ionic polarization is ignored, the result reduces to that of Landau-Devonshire theory.