ANOMALOUS ELECTRICAL BEHAVIOR OF PARTIALLY CARBONIZED POLYACRYLONITRILE FIBERS

Partially carbonized polyacrylonitrile fibers were observed to undergo a resistivity change of 2 to 4 orders of magnitude at a transition temperature typically in the range of 98 degrees C to 200 degrees C. The current-voltage curves exhibited an initial supercurrent-like increase, followed by a rapid drop to a high resistance state, and then a rise in current again at a later stage. These phenomena cannot be interpreted by existing theories on switching in inorganic amorphous semiconductors. They are explainable if the microstructure of the pyrolyzed fiber is viewed as comprising nanometer-scale superconducting phases interspersed with semiconducting phases, much like a large number of Josephson junctions connected in series.