Electrical resistance in thecdirection of graphite

The c-axis resistivity (${\rho }_c$) and its temperature dependence of highly oriented pyrolytic graphite have been studied in connection with the characteristic stacking-fault structure. In order to account for the observations, the pioneering theory of Ono on the tunneling conduction through the stacking-fault planes is reformulated using the concept of effective fault spacing. It is proposed further to add two mechanisms to the Ono theory; one is interlayer charge transfer through the impurity-assisted hopping of carriers similar to that previously considered for graphite intercalation compounds, and the other is thermal excitation of carriers across the low potential barrier formed on each fault plane. All the data have been satisfactorily reproduced by the curve fitting based on the formula consisting of these three conduction components. Also, the change of ${\rho }_c$ in the presence of high pressure is pointed out to be qualitatively explainable in terms of the tunneling associated with the pressure dependence of Slonczewski-Weiss band parameters.