Bismuth metal dispersed in insulating or semiconducting matrix shows PTCR properties at the melting point of bismuth metal of about 270°C. In this study, the optimum sintering conditions of bismuth metal/strontium-bismuth-titanate ceramics composites were investigated and quantitative analysis of the resistivity of the composites was performed by General Effective Media (GEM) equation. A sample of 0.73Bi-0.27SrBi4(Ti0.95Nb0.05)4O15 sintered at 1398 K for 2 h in Ar atmosphere shows PTCR property of about 5 orders of magnitudes and good cycle property. A relation between the resistivity of composite and the volume fraction of Bi metal particles in a series of xBi-(1-x) SrBi4(Ti0.95Nb0.05)4O15 was explained by percolation theory. But calculated PTCR properties from the shrinkage of Bi metal of 3.35% at the melting point are less than one order of magnitude, and therefore, the PTCR properties in this study can not be explained simply by decrease of the volume fraction of Bi metal because of the shrinkage at the melting point.
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