Piezoresistivity of magnesia-graphite composite ceramics

Magnesia-graphite composite ceramics were fabricated by hot pressing in Ar atmosphere, and their electrical properties were measured. The electrical resistivity increases as the graphite volume fraction x decreases, following well-accepted power law model based on the percolation theory. Renormalized pressure coefficient of resistance, d(ln R)/dP, decreases as x decreases. This behavior can be explained by the strong enhancement of d(ln p)/dx toward the percolation threshold. By fitting the x dependence of d(ln R)/dP with a theoretical equation, the Young's modulus of the composites was estimated.