Abstract
Definite electric field-induced birefringence has been observed in the vicinity of single grain boundaries with a distinct positive temperature coefficient of resistivity (PTCR) characteristic in semiconducting barium titanate (BaTiO 3 ) ceramics above the Curie point ( T c = 120°C). Both the highest temperature up to which birefringence could be observed and the temperature giving the maximum resistivity of the PTCR characteristic shifted to higher temperatures with increasing electric field in almost the same manner. Single grain boundaries examined in this study were formed in thin semiconducting BaTiO 3 bars with a diameter of 50-100 w m. The observed birefringence clearly demonstrates that spontaneous polarization ( P s ) induced by electric field can exist in the vicinity of grain boundaries in semiconducting BaTiO 3 ceramics even above T c . Based on the obtained results the mechanism of the PTCR effect may be interpreted by a model that P s plays a decisive role in the determination of the grain-boundary potential barrier height even above T c .
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