Mechanism of crystal-symmetry dependent deformation in ferroelectric ceramics: Experiments versus model

Abstract

In this paper, we investigate the mechanism of crystal-symmetry dependent deformation in ferroelectrics both experimentally and theoretically. We fabricated three types of Pb(ZrxTi1-x)O3 ceramics including the tetragonal (PZT45/55), the rhombohedral (PZT60/40), and the morphotropic (PZT52/48), where the tetragonal and rhombohedral phases coexist. X-ray diffraction and piezoresponse force microscopy were performed to characterize the crystal structures and domain patterns. Deformation of both poled and unpoled PZT ceramics was tested under bipolar electric fields and uniaxial compression, respectively. It is found that in both loading cases, the deformation of the morphotropic PZT is obviously larger than that of the tetragonal and rhombohedral PZT. As to the latter two, the electric field induced strain in the tetragonal PZT is smaller than that in the rhombohedral PZT, while the compression induced strains show the opposite tendency. To explore the observed crystal-symmetry deformation mechanism, we employed a previously proposed optimization-based constrained domain-switching model to simulate the experimental results. Domain switching in this model is realized by an optimization process to minimize the free energy of each grain. The constraint from neighboring grains is considered in an Eshelby inclusion manner, which is inherently crystal-symmetry dependent. The simulation results fit well with our experimental results without any fitting parameters, which indicate that the constrained domain-switching is responsible for the crystal-symmetry dependent deformation mechanism in ferroelectric ceramics.