Electrical resistivity and magnetoresistance of carbon/graphite fibers intercalated with nitric acid and arsenic pentafluoride

A series of high performance, experimental carbon/graphite fibers was intercalated and examined with respect to their metallic conductivity behavior by resistivity and magnetoresistance versus temperature measurements. One fiber was a polyacrylonitrile (PAN)-type precursor and three were pitch base precursors. All four types showed substantially similar behavior in the pristine state with respect to room temperature resistivity and the sign and magnitude of the temperature coefficient of resistivity. After intercalation with either nitric acid or nitric acid followed by AsF₅, the PAN-based fibers displayed a resistivity versus temperature behavior qualitatively similar to their pristine counterparts but displaced to lower resistivity. On the other hand, the pitch fibers with the same intercalation treatment exhibited metallic behavior (a positive temperature coefficient of electrical resistivity and a small magnetoresistance). These manifestations of metallic behavior are usually indicative of some three dimensional graphite structure in the carbon fibers.