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Electrical resistivity and its temperature variation are measured for lead zirconate titanate ceramics containing various metal oxides as impurities. The impurities can be classified from their influence on the resistivity of ceramics into the following three groups. (1) Impurities which keep the resistivity nearly unchanged ( e.g. Fe 2 O 3 ). (2) Impurities which increase it enormously because of electron-hole compensation ( e.g. Nb 2 O 5 ). (3) Impurities which increase it at first (electron-hole compensation) and then decrease it ( e.g. Cr 2 O 3 ). The decrease of resistivity in group (3) seems to be caused by the generation of segregated impurity layers which enclose the grains in ceramics. This postulate is confirmed quantitatively by the measurements of resistivity of the ceramics in which impurities are injected by means of thermal diffusion.
Masao Takahashi (1971) studied this question.