EFFECT OF CHARGE REDISTRIBUTION THROUGH SECONDARY PHASE-FORMATION ON PTCR CHARACTERISTICS OF N-BATIO3 CERAMICS

Heterogeneous addition of alumina, up to 10 mol%, as a grain boundary modifier in nBaTiO(3) PTCR ceramics modifies the rho-T characteristics whereby T-max is shifted from 455 to 700 K, accompanied by the decrea se in rho(max). Whereas B2O3 shifts the T-max to 410 K with little cha nge in rho(max). The grain boundary segregation of alumina leads to th e formation of secondary phases, BaAl6TiO12 and Ba3Al10TiO20. The chan ging pattern of trap states is evident from the presence of Ti4+-O--Al 3+ type hole centers at the grain boundary layer regions, as identifie d by the EPR spectra. The charge redistribution among the inter-band g ap defect states across the Curie temperature is substantiated by the EPR results. (C) 1998 Elsevier Science B.V.