Giant piezoresistivity of polymer-derived ceramics at high temperatures

The piezoresistivity of a silicon oxycarbonitride polymer-derived ceramic (PDC) material is investigated at high temperatures. The resistance was measured as a function of uniaxial loading under constant current conditions. The piezoresistive gage factor was found to be in the range of 600–1700 at an applied stress of 1 MPa. The gage factor depends on both the stress and temperature. The piezoresistivity was measured up to 1000 °C, demonstrating the viability of PDCs as piezoresistive materials at high temperatures. The Arrhenius dependence of the gage factor, ψ, gives the following expression for its temperature dependence at 1 MPa: ψ = 44 exp(28,000/8.31T), where T is in Kelvin. The extrapolated values of the gage factor yield a value of 322 at 1400 °C, and 287 at 1500 °C (at an applied stress of 1 MPa). A combination of stability at high temperatures, chemical durability, and large gage factor are entirely unique to PDCs making them ideal candidates for sensor materials in extreme environments.