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

Domains exist in ferroelectric ceramics. External loads, such as electric field and stress, can cause domain switching. Domain switching always results in nonlinear ferroelectricity and ferroelasticity of ferroelectric ceramics. In this investigation, nonlinear electric-mechanical behavior related to ferroelectric and ferroelastic domain switching is experimentally and theoretically studied. In the experimental work, the electric-mechanical response of a soft PZT ferroelectric ceramic subjected to combined electric-mechanical loads was observed. The effect of different compressive stress levels on the electromechanical response was examined. In the theoretical modelling, the orientation of each domain is defined by its local coordinate relative to a fixed global coordinate. Orientation distribution function (ODF) is used to describe the domain pattern. For mathematical simplicity, the Reuss average is used in the modelling. According to the proposed theory, a domain has different Gibbs' energy at different orientation states and the energy difference forms the domain switching driving force. The domain pattern and its evolution are determined by the joint action of the domain switching driving force and the dissipation during domain switching. In ferroelectricity and ferroelasticity, 90 degrees and 180 degrees domain switchings play different roles and have different switching dissipations associated with them. A criterion considering the difference between the 90 degrees switching and the 180 degrees switching is established by the thermodynamic approach. There is an agreement between theoretical and experimental results. It should be pointed out that the micromechanical model proposed in this paper is restricted to ferroelectric materials exhibiting transformation from cubic to tetragonal only. (C) 1999 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.