STUDY OF FERROELECTRICITY IN THE PMN PT SYSTEM NEAR THE MORPHOTROPIC PHASE-BOUNDARY

The ferroelectric properties of tetragonal phase Pb (Mg1/3Nb2/3)O3 PbTiO3 (PMN-PT) solid solutions have been investigated. The coercivity, E(c), increases monotonically with PT content. The remanent polarization, P(r), on the other hand, decreases rapidly with PT content and reaches a minimum value for a sample containing 0.365 mol% PT. It increases moderately when the PT content is further increased. The deformation parameter, delta, is used to correlate the composition to ferroelectric characteristics of these materials. A critical deformation parameter, delta(c) = 0.008984, is observed at which the remanent polarization contributed from Mg2+ and Nb5+ cations, p(r)MN, decreases with delta value when delta < delta(c) and vanishes when delta > delta(c). The remanent polarization contributed from Ti4+ cations, p(r)Ti, on the other hand, increases with delta value, following the trend p(r)Ti = kdelta1/2 . The rattling of Mg2+ and Nb5+ cations among off-centred sites in oxygen octahedra is adapted to explain such a phenomenon.