Cooperative interaction of oxygen octahedra for dielectric properties in the ferro-paraelectric composites

In the PbZn_1/3Nb_2/3O₃ relaxor system, A-site modified ferroelectric perovskite Pb_0.7Ba_0.3 Zn_1/3Nb_2/3O₃ phase which was substituted with 0.3 mol of Ba to Pb site and paraelectric pyrochlore Pb_1.83Zn_0.29Nb_1.71O_6.39 phase were prepared and the composites with the perovskite and pyrochlore phase were synthesized. The dielectric properties with respect to the volume percent of the phase were examined. The percolation limit where ferroelectric perovskite phase is isolated by paraelectric pyrochlore phase was 29.6 vol%. However, a dielectric anomaly was observed below the percolation limit, which is believed to be caused by a factor that can propagate any ferroelectric lattice vibration mode from the isolated ferroelectric perovskite phase to paraelectric pyrochlore matrix. 3-dimensional connection of oxygen octahedron by its corner sharing seems to play an important role for the cooperative dielectric interaction that contributes to the dielectric anomaly. Furthermore, highly polarizable Pb²⁺ ions in the composite help the propagation efficiency.