Abstract
(Bi0.85Sr0.15)4(Ti0.95Nb0.05)3O12 shows a large positive temperature coefficient of resistivity (PTCR) properties of almost 4 orders of magnitude at about 543 K. This temperature does not correspond to the Curic point of Bi4Ti3O12, but to the melting point of Bi metal. The microstructure of samples with or without showing PTCR properties observed by optical microscopy, showd the presence of Bi metal distributed in matrix. The various resistivity-temperature characteristics were obtained by controlling the distribution Bi metals in the matrix. Therefore, the new appearance of PTCR properties in Bi–Sr–Ti–O system would be related with the melting and solidification of Bi metal which is finely distributed in samples and isolated for each other. The equivalent electrical circuit for the samples were determind by complex impedance and modulus analysis. A model of this appearance of PTCR properties is proposed from these results as follows; Electrical current would flow in Bi metal at lower temperatures, but would not flow at higher temperatures. The resistivity of the sample at higher temperatures would be determined by matrix. Another RC component which acts only in the vicinity of PTCR temperature was also observed. This component may be due to the interface of Bi metals and the matrix.
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