PTCR anomaly in barium-titanate-based composites

We have identified a PTCR anomaly in undoped BaTiO3 (BT) ceramics. This anomaly was ascribed to a disconnection of the semiconducting grains, due to dimensional changes of the BT grains at the Curie point, in a composite composed of two constituent BT phases, one with a low electrical resistivity and the other with a high electrical resistivity. The composite exhibits a significant PTCR effect of three orders of magnitude at the Curie temperature. Using a similar approach, a PTCR anomaly was observed in a composite where copper was used as the conductive matrix, while BT particles were used as the second constitutive phase in the composite, acting as a circuit-breaker, and disconnecting the continuous conducting phase at the Curie temperature.