Direct Examinations of PTC Action of Single Grain Boundaries in Semiconducting BaTiO 3 Ceramics

R‐T and I‐V characteristics of single grains and grain boundaries in large‐grained BaTiO 3 PTC ceramics were studied with a two‐probe technique using a micromanipulator and fine Al wire. The PTC originates in the grain boundary only and behaves differently in each boundary. Even below T c , the ceramic resistance depends almost entirely on the boundary. I‐V characteristics in the boundary follow Ohm's law and conduction by a space‐charge‐limited current with a trap, using different applied voltages. The PTC anomaly relates to activation of the trap in the boundary, not to barrier height. A band model in the intergranular layer, with dielectric BaTiO 3 and the trap, is proposed.