INVESTIGATION OF THE PTCR EFFECT IN ZNO-NIO 2-PHASE CERAMICS

A positive temperature coefficient of electrical resistivity (PTCR) in ZnO-NiO ceramics was observed and an attempt to explain its origin wa s made. According to electrical measurements, supported by dilatometri c and microstructural investigations, the percolation principle was us ed for this purpose. A series of samples with different ZnOss and NiOs s contents were prepared. The electrical resistivity of the samples wa s measured at different temperatures. ZnOss represents a low ohmic and NiOss represents a high ohmic phase. Monophase samples exhibited a st rictly negative temperature coefficient of electrical resistivity (NTC R), while in some two-phase samples PTCR behaviour was observed. Resul ts of electrical, dilatometric measurements and microstructural invest igations indicated a possible explanation of PTCR behaviour on the bas is of the percolation model.