Domain Observation in Pb(Zn_1/3Nb_2/3)O₃–PbTiO₃Mixed Crystals

Abstract

Domain-wall structures in the vicinity of the morphotropic phase boundary (MPB) in (1-x)Pb(Zn1/3Nb2/3)O3–xPbTiO3 (PZN–xPT) mixed crystals (x=5% and 8%) were investigated by means of a polarizing microscope. It was found that the apparent jump of the indicatrix rotation as a function of temperature appears in the MPB region (x=8%) without the poling process, indicating the occurrence of a phase transition between the tetragonal and rhombohedral phases, despite the fact that this transition is known to be observed only in a poled sample in the case of dielectric constant measurements. We concluded that the sharp phase transition between the tetragonal and rhombohedral phases in the PZN–PT crystal can be observed in the small region of 50 µm order even without the poling process. It was also found that the principal axis of the indicatrix slightly rotates in the MPB region, implying the appearance of the lower symmetry phase such as a monoclinic structure.