Anisotropy of electrical conductivity in aluminum trichloride–intercalated graphite

We have examined the basal-plane and c-axis electrical resistivity (${\rho }_a$ and ${\rho }_c$) of first-, second-, and fourth-stage (s) graphite intercalation compounds containing aluminum trichloride from 4.2≤T≤295 K. The basal-plane results are similar for all stages: ${\rho }_a$ is a nonlinear function of T, and all ρ(295 K)/ρ(4.2 K) values are less than 10. The ${\rho }_c$(T) behavior is stage dependent: for s=1, ${\rho }_c$(T) varies approximately as ${\rho }_a$(T), but is (3–8)×${10}^5$ times as great; whereas, for s=2, ${\rho }_c$ diminishes linearly as T decreases, undergoes a sharp transition at ∼186 K, and again decreases linearly with a reduced slope. Liquid-helium anisotropy values in second-stage materials can attain 3×${10}^6$. The thermal variation of ${\rho }_c$ is shown to be a function of the low-temperature value for both first- and second-stage products. The data are compared to results of recent conduction-electron spin-resonance studies, and possible conductivity mechanisms are discussed.