Electrical resistivity of Cr–Al2O3 and ZrxAly–Al2O3 composites with interpenetrating microstructure

AC and DC resistivity of Cr–Al2O3 and ZrxAly–Al2O3 composites with varying metal content were measured. A strong percolation behavior was observed in the Cr–Al2O3 system, where the AC resistivity varied nine orders of magnitude close to the percolation threshold of 28 vol.%. AC measurements were less dependant on the contact resistance than DC measurements. The best reproducibility was obtained at a frequency of 100 kHz. AC resistivity values of insulating composites differed from DC values and may also be frequency-dependant. DC measurements up to 600 °C indicate that the intermetallic phases ZrAl3 and ZrAl are PTC conductors. The electrical properties of ZrxAly–Al2O3 samples with a metal content of 29 vol.% were anisotropic, with a much higher resistivity in the pressing direction.