Less than mm2 macrosymmetry in polarized (011)-oriented relaxor-PbTiO3 single crystals reflected in the face shear properties

Abstract

The macrosymmetry of (011)-oriented nominally rhombohedral relaxor-PbTiO3 single crystals poled along the [011] direction is investigated using the impedance spectroscopy method. Contrary to the common belief on the mm2 macrosymmetry, we find that the mm2 macrosymmetry significantly underestimates the electromechanical coupling of the 𝑍𝑋𝑡 45°-cut transverse extension specimen by about 10%. We show that the underestimated electromechanical coupling can be corrected by assigning a lower symmetry of 2, i.e., an average monoclinic symmetry. The validity of the newly assigned macrosymmetry and the presence of non-regular phases presumably responsible for the apparent loss of mirror symmetry are confirmed by radial strain and thermally stimulated depolarization measurements, respectively.