Ferroelectricity of Pb(Zn1/3Nb2/3)O3-BaTiO3-PbTiO3 ceramics in the vicinity of morphotropic phase boundary

The morphotropic phase boundary (MPB) in the (0.85 – x)Pb(Zn_1/3Nb_2/3)O₃ – 0.15BaTiO₃ – xPbTiO₃(0 < x < 0.2) ceramic system was delineated by x-ray diffraction analysis. Polarization hysteresis loop measurements at room temperature were performed for compositions in the vicinity of the MPB. Experimental results demonstrate that the MPB, by its definition the rhombohedral and tetragonal phase coexist in the present system, is a broad composition region where the value of x ranges from 0.12 to 0.18. The remanent polarization, P _r, increases with PbTiO₃(PT) reaching a maximum value of 18 C/cm² at 15 mol%PT, then decreases remarkably with further PT addition, whereas the variation of coercive field, E _c, with PT content shows the opposite trend. The effect of PT incorporation on P _r is more pronounced than on E _c. Correlation between the degree of lattice distortion, instead of the maximization of the polarization orientations inherent to both phases, and P _r is attained to account for the observed phenomenon. The dependence of E _c upon PT content, however, reflects the transition from typical relaxor ferroelectrics to weak normal ferroelectrics, as confirmed by the results of the dielectric measurement.