Intrinsic electromechanical properties of ferroelectric ceramics with the coexistence of tetragonal and rhombohedral phases near the morphotropic phase boundary

摘要

A model for electromechanical properties of ferroelectric ceramics with the coexistence of tetragonal and rhombohedral phases near the morphotropic phase boundary (MPB) is presented explicitly in this paper. With the probability density function of orientation and the domain switching criterion, the three-dimensional orientation space is divided into subfields for 14 types (6 for tetragonal and 8 for rhombohedral phase, respectively). According to the polarization components P_T~O for tetragonal phase and P_R~O for rhombohedral phase derived from the Landau-Devonshire free energy function, we introduce the ratio of spontaneous polarizations A = P_r~O/P_t~O, covering all possible situations near MPB, so that electromechanical properties with the coexistence of two phases are treated in a united way. This model makes it possible to estimate the effect of phase coexistence on intrinsic part of the ferroelectric properties. A specific example is also included.