Semiconductivity and Diamagnetism of Polycrystalline Graphite and Condensed Ring Systems

Abstract

The analysis of results obtained from studies of electric resistivity as a function of temperature, and sample preparation, and of other available evidence, leads to a clarification of the electronic processes in the class of substances extending from condensed ring molecular solids to polycrystalline graphite. In all these solids, the electric current flows preferentially along the benzene-ring planes. Scattering of electrons is due to thermal lattice vibrations and to the boundaries of molecular planes, where electrons pass through potential barriers into the neighboring crystallites. These barriers are quite transparent in polycrystalline graphite and baked carbons, since the flow occurs along the carbon-carbon bonds, but are quite opaque in molecular solids where the barriers are due to the presence of foreign atoms attached at the periphery of the molecules.