Ferroelectricity of Pb(Zn1/3Nb2/3)O-3-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)O-3 - 0.15BaTiO(3) - xPbTiO(3)(0 < x < 0.2) ceramic system was delineated by x -ray diffraction analysis. Polarization hysteresis loop measurements at roo m temperature were performed for compositions in the vicinity of the MPB. E xperimental results demonstrate that the MPB, by its definition the rhomboh edral and tetragonal phase coexist in the present system, is a broad compos ition region where the value of x ranges from 0.12 to 0.18. The remanent po larization, P-r, increases with PbTiO3(PT) reaching a maximum value of 18 m uC/cm(2) at 15 mol%PT, then decreases remarkably with further PT addition, whereas the variation of coercive field, E-c, with PT content shows the opp osite 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 th e maximization of the polarization orientations inherent to both phases, an d 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. (C) 2001 Kluwer Academic Publishers.