SEMICONDUCTOR CERAMIC AND POSITIVE TEMPERATURE COEFFICIENT THERMISTOR

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Disclosed is a semiconductor ceramic which is mainly composed of a BamTiO3 composition having a perovskite structure represented by the following general formula : AmBO3, wherein a part of Ba constituting the site A is substituted by Na, Bi, Ca and a rare earth element having a smaller ionic radius than Na, the content the rare earth element is within the range of 0.0005-0.015 in terms of molar ratio when the total mole number of the elements constituting the site A is taken as 1 mole, and the Ca content is within the range of 0.05-0.20 (preferably not less than 0.125 but not more than 0.175) in terms of molar ratio when the total mole number of the elements constituting the site A is taken as 1 mole.  Also disclosed is a PTC thermistor wherein a component element (1) is formed from the semiconductor ceramic.  Consequently, the semiconductor ceramic can have good reliability even though an alkali metal element is contained therein.