Effect of electric-field-induced polarization on positive temperature coefficient of resistivity characteristics of semiconducting barium titanate ceramics

We observed distinct electric-field-induced birefringence in the vicinity of single-grain boundaries of semiconducting BaTiO3 above the Curie temperature (T-e; 120 degreesC); the single-grain boundaries exhibited a distinct positive temperature coefficient of resistivity (PTCR) anomaly in the same temperature range. The highest temperature at which we could observe birefringence shifted to higher temperatures with increasing electric field, and the maximum resistivity temperature of the PTCR characteristics also shifted to higher temperatures with increasing electric field. Electric field dependencies of the highest temperature of observed birefringence and the maximum resistivity temperature were found to be quite similar to each other. These results suggest that polarization induced by residual strain and/or electric field can exist in the vicinity of grain boundaries in semiconducting ceramics even above 120 degreesC (the inherent T-e of the bulk), and that the occurrence of the PTCR characteristics is closely related to the induced polarization.