Nonlinear electric-mechanical behavior and micromechanics modelling of ferroelectric domain evolution

Domains exist in ferroelectric ceramics. External loads, such as electric f ield and stress, can cause domain switching. Domain switching always result s in nonlinear ferroelectricity and ferroelasticity of ferroelectric cerami cs. In this investigation, nonlinear electric-mechanical behavior related t o ferroelectric and ferroelastic domain switching is experimentally and the oretically studied. In the experimental work, the electric-mechanical respo nse of a soft PZT ferroelectric ceramic subjected to combined electric-mech anical loads was observed. The effect of different compressive stress level s on the electromechanical response was examined. In the theoretical modell ing, the orientation of each domain is defined by its local coordinate rela tive to a fixed global coordinate. Orientation distribution function (ODF) is used to describe the domain pattern. For mathematical simplicity, the Re uss average is used in the modelling. According to the proposed theory, a d omain has different Gibbs' energy at different orientation states and the e nergy difference forms the domain switching driving force. The domain patte rn and its evolution are determined by the joint action of the domain switc hing driving force and the dissipation during domain switching. In ferroele ctricity and ferroelasticity, 90 degrees and 180 degrees domain switchings play different roles and have different switching dissipations associated w ith them. A criterion considering the difference between the 90 degrees swi tching and the 180 degrees switching is established by the thermodynamic ap proach. There is an agreement between theoretical and experimental results. It should be pointed out that the micromechanical model proposed in this p aper is restricted to ferroelectric materials exhibiting transformation fro m cubic to tetragonal only. (C) 1999 Acta Metallurgica Inc. Published by El sevier Science Ltd. All rights reserved.