Electrical resistivity of Cr-Al2O3 a interpenetrating and ZrxAly-Al2O3 composites with 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 degreesC 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. (C) 2002 Elsevier Science Ltd. All rights reserved.