Increasing resistivity of electrically conductive ceramics by insulating grain boundary phase.

Increasing resistivity of electrically conductive nonoxide ceramics was investigated by insulating conductive pathways through conductive grains in a sintered body by addition of an insulating grain boundary phase, which was produced by the reaction of sintering additives in liquid phase sintering. When SiC was hot pressed with an additive of 10 vol % of Al2O3 and Y2O3, the resistivity decreased as sintering temperature increased owing to contact between SiC grains during densification. However, by hot pressing at 1750°C, a high resistivity of greater than 1 × 10(11) Ω cm was achieved because of the penetration of an insulating grain boundary phase between the SiC grains. It is possible to fabricate high-resistivity SiC ceramics without losing their excellent mechanical properties by introduction of an insulating grain boundary phase, the volume of which is approximately 1/7 that of the insulating phase incorporated in conventional ceramic composites.