The Properties of the Interstitial Compounds of Graphite. III. The Electrical Properties of the Halogen Compounds of Graphite

Abstract

The presence of lamellar or of residual bromine in artificial graphite reduces the resistance, the absolute magnitude of its temperature coefficient near room temperature, and the magneto resistance. The Hall coefficient increases and eventually changes from negative to positive values. The changes resemble very closely those obtained in the oxidation of graphite in sulfuric acid. This similarity in properties suggests that the electron acceptors in these compounds are only weak scattering centers for conduction electrons. Since the electrical properties of graphite bisulfate and of graphite bromide are very similar, it may be assumed that both compounds are of a similar type. Since the bisulfate compound is ionic in nature, the bromine in graphite bromide is also probably ionized. On this assumption the graphite bromides have the formulas C_nBr·3 Br₂ for the lamellar and C_nBr·2.25 Br₂ for the residue compounds. Chlorine reacts with graphite at low temperatures only. The properties of the compounds of chlorine and graphite resemble in all respects those of the compounds of bromine and graphite. Attempts to react iodine and graphite have failed. Iodine chloride, however, reacts rapidly with graphite.