Structural and Phase Transitions in the High Composition Domain of the System (1-x)Pb(Mg_(1/3)Nb_(2/3))O_3-xPbTiO_3

摘要

Raman scattering, dielectric studies, powder and single crystal X-ray diffraction on 0 .6Pb(Mg_(1/3)Nb_(2/3)O_3-0.4PbTiO_3 ( PMN-40PT) and 0.55 Pb(Mg_(1/3)Nb_(2/3))O_3-0.45PbTiO_3 (PMN-45PT) were carried out over a wide temperature range. Dielectric plots of PMN-45PT revealed two phase transitions with a sharp maximum at T_c (paraelectricferroelectric transition at 485 K, from cubic to tetragonal with respective space groups Pm-3m and P4mm similar to PMN-40PT) and a second broad Raman shift at around 225 K. The Raman investigations confirmed the existence of phase transitions in PMN45PT crystals, and the lowest frequency behaves like a soft mode. The appearance of diffuse scattering at room temperature in PMN-45PT suggests a phase distinct from PMN-40PT below T_c. The identification of the symmetry in this temperature region will be further demonstrated.