Some electronic properties of polyacrylonitrile-based carbon fibres

The resistivity, thermoelectric power and magnetoresistance of carbon fibres derived from a polyacrylonitrile-based precursor heat treated to between 1000°C and 2800°C have been examined. The resistivity ratio as a function of heat treatment temperature exhibits a broad minimum roughly at about a heat treatment temperature (HTT) of 1750°C, and both the thermoelectric power and the magnetoresistance undergo a change of sign at that temperature. The importance of the temperature 1750°C, at which fundamental structural changes are believed to take place, is examined in the light of existing band models in the carbon and amorphous semiconductor fields.