Volume fraction and whisker orientation dependence of the electrical properties of SiC-whisker-reinforced mullite composites

The electrical behavior of hot-pressed mullite composites reinforced with 10, 20, and 30% SiC whiskers (SiCw) was evaluated in the frequency range 100 Hz-10 MHz and compared with 2 GHz data as well as dc resistivity measurements. It is found that the addition of SiCw has a dramatic effect on the dielectric properties as well as the resistivity of these materials. The ac properties (dielectric constant, dielectric loss, and impedance) show a strong dependence on the volume fraction of SiC and on the orientation of the electric field with respect to the hot-pressing direction and hence the whisker orientation. The dc resistivity measurements are sensitive to the whisker volume fraction but cannot easily discriminate between those samples that were measured parallel or perpendicular to the hot-pressing direction as was possible with the ac measurements.