The phase transition sequence and the location of the morphotropic phase boundary region in (1   x)[Pb (Mg1/3Nb2/3)O₃] xPbTiO₃single crystal

Piezoelectric constant and temperature-dependent dielectric constant measurements have been performed on ⟨110⟩-oriented (1 − x )Pb (Mg 1/3 Nb 2/3 )O 3 – x PbTiO 3 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 M A –monoclinic M C –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 P m .