The phase transition sequence and the location of the morphotropic phase boundary region in (1 x)[Pb (Mg_1/3Nb_2/3)O₃] xPbTiO₃single crystal

Abstract

Piezoelectric constant and temperature-dependent dielectric constant measurements have been performed on ⟨110⟩-oriented (1 − x)Pb (Mg1/3 Nb2/3)O3–xPbTiO3 crystals with different compositions under different poling fields. The width of the morphotropic phase boundary region (0.30 < x < 0.35) is determined on the basis of two abnormal regions of the dielectric and piezoelectric properties. An irreversible rhombohedral–monoclinic MA–monoclinic MC–tetragonal phase transition sequence was observed directly from the dielectric constant versus temperature results for ⟨001⟩-poled rhombohedral crystals with compositions near the rhombohedral–monoclinic phase boundary. The structure of the morphotropic phase is shown to be monoclinic with space group Pm.