STRONG FERROELECTRIC PEROVSKITE PHASE IN PB-CONTAINING COMPOSITES

Composites with ferroelectric and non-ferroelectric phases were synthe sized by changing the volume percent of the phases and the dielectric properties were investigated. New factors influencing the dielectric p ermittivity of the composites were considered for the application and design of high performance dielectric composites. The percolation limi t, which depends on the morphology and connectivity of the phase, show ed similar values for Pb0.7Ba0.3(Zn1/3Nb2/3)O-3 - Pb1.83Zn0.29Nb1.71 O -6.39 and BaTiO3-Ba6Ti17O40 diphasic composites. However, the critical point for Pb0.7Ba0.3(Zn1/3Nb2/3)O-3-Pb1.83Zn0.29Nb1.71O6.39, which ex hibited a dielectric anomaly, had a lower value than that of the perco lation limit. The dielectric anomaly, which was observed below the per colation limit, is believed to be caused by a factor that can propagat e any ferroelectric lattice vibration mode from the isolated ferroelec tric phase to the non-ferroelectric matrix. The dielectric anomaly see ms to depend on the connection between oxygen octahedra. Therefore, wh en the oxygen octahedra make a three-dimensional connection by corner sharing in the composite, the dielectric anomaly appears even when the volume percent of the ferroelectric phase is low. In particular, in P b-based systems such as Pb0.7Ba0.3(Zn1/3Nb2/3)O-3-Pb1.83Zn0.29Nb1.71O6 .39, the critical point exhibited the lowest value because the highly polarizable Pb2+ ions may also contribute to the propagation of the fe rroelectric lattice vibration mode. (C) 1998 Elsevier Science B.V. All rights reserved.