Orientation dependence of resistivity in anisotropic ceramic composites

Anisotropic ceramic composites, composed of an alumina matrix containing various ratios of silicon carbide whisker inclusions, were measured using impedance spectroscopy and pole figure analysis. The impedance spectra were found to contain two semicircles: one at high frequencies, corresponding to bulk impedance phenomena; and one at low frequencies, corresponding to interfacial phenomena. The bulk resistivity of samples measured parallel to the hot-pressing direction showed a dramatic decrease in resistivity at a volume fraction of 8-10% SiCw. The degree of sample anisotropy, as measured by taking bulk resistivity values parallel and perpendicular to the hot-pressing direction, was found to increase as SiCw volume fraction decreased towards the percolation threshold. The electrical property anisotropy was confirmed by texture analysis. Pole figure data for composites containing 10 and 20% volume fraction SiCw showed fairly consistent whisker orientation distributions for both measured orientations.