Composite ceramics with a positive temperature coefficient of electrical resistivity effect

Composite ceramics with compositions within the ZnO-NiO-TiO2, ZnO-MgO, and ZnO-Ln(2)O(3) (Ln = Nd, Sm) systems were found to exhibit an anomalous posi tive temperature coefficient of electrical resistivity (PTCR)effect. The in vestigations revealed, that in all cases when the PTCR effect was identifie d, the composite ceramics were found to be composed of phases with differen t electrical resistivities and linear thermal expansion coefficients. Therm al mismatch between the phases in the composites leads to a disconnection o f the grains of the low:resistivity constituent phase on account of the hig h thermal expansion of the other high resistivity constituent phase, result ing in a PTCR effect.