Mechanism for c-axis conduction in graphite intercalation compounds.

The four-probe technique is used to measure the c-axis resistivity of various stages of ${\mathrm{FeCl}}_{3}$ acceptor graphite intercalated compounds. A comprehensive investigation of the resistivity behavior between room and liquid-helium temperatures for stages 2--5 and 9 and highly oriented pyrolytic graphite is presented. The data show a low-stage dependence where the resistivity increases with temperature, an intermediate stage where the temperature variation of the resistivity is small, and a high-stage dependence where the resistivity decreases with temperature. In our case, stage 5 plays the role of the intermediate stage. Stage 5 also exhibits the highest room-temperature resistivity. The c-axis resistivity data are analyzed in terms of the variable-range hopping-conduction model in parallel with band conduction.