Dielectric and piezoelectric properties of the thermally annealed Pb(Zn,Mg)_1/3Nb_2/3O₃–PbTiO₃ system across the rhombohedral/tetragonal morphotropic phase boundary

Effects of thermal annealing on the dielectric/piezoelectric properties of Pb(Zn,Mg)_1/3Nb_2/3O₃-PbTiO₃ ceramics (PZMN-PT with Zn/Mg = 6/4) were examined across the rhombohedral/tetragonal morphotropic phase boundary (MPB). Examination of the lattice parameters and the rhombohedral angle indicated that the MPB is in the vicinity of 24 mol% PbTiO₃. Both the relative dielectric permittivity (∊_r) and the piezoelectric constant (d₃₃)/electromechanical coupling constant (k_p) were increased by thermal annealing (800–900 °C) after sintering at 1150 °C for 1 h. The observed improvements in the dielectric and piezoelectric properties were attributed to the elimination of PbO-rich amorphous intergranular layers (about 1 nm thickness) induced by thermal annealing. Both the dielectric analysis using the series mixing model and the microscopic examination by transmission electron microscopy supported this conclusion.