Factors and Mechanisms Affecting the Positive Temperature Coefficient of Resistivity of Barium Titanate

The chemistry of semiconducting lanthanum‐doped barium titanate was examined to determine the factors critical to the positive temperature coefficient of resistivity exhibited by this material. This phenomenon was sensitive to oxidation under certain nonequilibrium conditions. Inhomogeneity is thought to result from such conditions and to produce regions of different resistivity throughout the ceramic body. The existence of high resistivity layers was demonstrated by analysis of dispersions in ac resistance at audio frequencies. Association of these layers with crystallite surfaces, i.e. grain boundaries, was demonstrated by resistivity measurements of semiconducting single crystals before and after oxygen treatments.