Charge transfer effects in acid salts of graphite

Abstract
Specimens of well oriented stress-annealed pyrolytic graphite mounted as electrical conductors have been oxidized under controlled conditions to give the acid salts, graphite nitrate and graphite bisulphate. Progressive intercalation in forming these compounds has been followed by measurements of the electrical resistivity, the magneto-resistance, and the Hall effect. Various electronic properties confirm a model for the acid salts in which layers of carbon hexagon networks act as macro-cations, separated by layers in which acid anions are linked to additional molecules of acid by hydrogen bonds. In conformity with this model, as the concentration rises, the resistance drops, at first steeply, finally asymptoting to a limiting value characteristic of a synthetic metal. The Hall effect which is negative for the near-ideal graphites used as starting materials passes through zero and finally becomes positive, confirming the general nature of the charge transfer hitherto assumed. The magneto-resistance measured at 6 kG decreases, to become practically zero as intercalation proceeds.

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