Features of ferroelectric states in the simple-perovskite mixed-oxide system (1-x)Pb(Zn_1/3Nb_2/3)O₃-xPbTiO₃with lower Ti contents

A mixed-oxide system (1 - x)Pb(Zn_1/3Nb_2/3)O₃-xPbTiO₃, which has a simple perovskite structure, has been reported to exhibit remarkable piezoelectric responses for 0 < x ≤ 0.08. To understand the ferroelectric states for 0 < x < 0.10, the crystallographic features of plate-shaped single crystals with various sample orientations have been examined by transmission electron microscopy. Owing to both the bending of specimens and the complicated nanometer-scale domain structures, it was difficult to obtain a contrast reversal due to the failure of Friedel's law. In some cases, however, it was possible to analyze the ferroelectric domain structures of the sample. Although the typical 109° domain structure of the ferroelectric rhombohedral state was found for x = 0.02, as a major feature in [110]c-oriented single crystals, the ferroelectric states for 0 < x ≤ 0.08 were found to be characterized by an assembly of nanometer-scale polar (NP) domains with rhombohedral symmetry. In [210]c-oriented crystals, on the other hand, the so-called MC state with monoclinic symmetry was present for x ≈ 0.08. Furthermore, on the basis of in-situ observation, the evolution of a mazepattern domain structure in the M_c state upon cooling from the paraelectric state occurs via a local flip-flop between two polarization vectors, which are nearly parallel to the 210_c directions. It is likely that this behavior is directly associated with the ultrahigh piezoelectric deformations found for x ≈ 0.08.