Factors to have an effect on the phase coexistence at the morphotropic tetragonal and rhombohedral phase boundary(MPB) of $Pb(Zr,Ti)O_3$ ceramics were investigated. And the packing arrangement of the tetragonal and the rhombohedral phase in the MPB PZT ceramics was studied with transmission electron microscope.
Two kinds of PZT ceramics with different chemical homogeneity were prepared by conventional solid state reaction and coprecipitation method. There was coexistence of the tetragonal and the rhombohedral phase over a wide composition range in the PZT ceramics prepared by conventional solid state reaction, but phase coexistence was not observed in coprecipitated PZT ceramics. Therefore compositional fluctuation is considered to be the primary reason of the phase coexistence of the tetragonal and rhombohedral phase in MPB PZT ceramics.
Structural phase transformation between ferroelectric tetragonal and rhombohedral state and domain rearrangement by mechanical stress and electric field were examined in $Pb(Zr,Ti)O_3$ ceramics by direct determination through X-ray diffraction analysis and theoretical calculation using phenomenological thermodynamic theory.
Tensile stress and/or electric field were calculated to shift MPB. The stable composition range of the phase of which spontaneous strain and spontaneous polarization aligned to the direction of tensile stress and/or electric field was expanded.
Mechanical stress applied to MPB PZT ceramics caused domain rearrangement by which polar axes aligned so that a part of the stress was able to be relieved, and structral phase transformation by which the phase coexistence region was broadened. Electric field also rearranged domains of the PZT ceramics. But any change of the phase coexistent composition range by the electric field was not observed in MPB PZT ceramics.
Fringe contrast in the bright field and doublet spot splitting in the selected area diffraction pattern, which were the typical characteristics of non-180℃ domain boundaries of ferroelectrics, were observed using transmission electron microscope in a MPB PZT ceramics. And in the other part of the sample triplet spot splitting was also observed, which represented the alternative array of non-180℃ domains of ferroelectric tetragonal and rhombohedral phase. This observation results from the fact that both of single phase regions and the regions which are composed of alternation of tetragonal and rhombohedral domains exist in a MPB PZT ceramics.