Composite ceramics with a positive temperature coefficient of electrical resistivity effect

Composite ceramics with compositions within the ZnO–NiO–TiO₂, ZnO–MgO, and ZnO–Ln₂O₃(Ln = Nd, Sm) systems were found to exhibit an anomalous positive temperature coefficient of electrical resistivity (PTCR) effect. The investigations revealed, that in all cases when the PTCR effect was identified, the composite ceramics were found to be composed of phases with different electrical resistivities and linear thermal expansion coefficients. Thermal mismatch between the phases in the composites leads to a disconnection of the grains of the low resistivity constituent phase on account of the high thermal expansion of the other high resistivity constituent phase, resulting in a PTCR effect.