High electrical conductivity in graphite intercalated with acid fluorides

Abstract

Unusually high room temperature electrical conductivity, higher than that of pure copper, has been observed under certain conditions in graphite intercalated with the strong acid fluorides, antimony pentafluoride and arsenic pentafluoride. Since these results are of considerable scientific and technological importance, and likely to affect the course of research in this area, the confirming experiments are reviewed here. The first experiment demonstrating the potential of these compounds was measurements on a composite wire consisting of an SbF 5 intercalated graphite powder core with a copper sheath [1]. Results were obtained by a d.c. four point resistance method on samples 1 mm dia. × 10 cm long. Comparison of this composite wire with a control sample of copper demonstrated convincingly the superior conductivity of the intercalated graphite core. More recent experiments of a similar nature have confirmed those early findings. We have also made measurements of highly oriented polycrystalline graphite (HOPG) intercalated with AsF 5 [2]. In careful measurements a contactless r.f. (100 kHz) induction technique has substantiated the high electrical conductivity of these materials. While the measured conductivity of the AsF 5 compounds has a maximum value only marginally greater than pure copper, this value must be regarded as conservative and any correction made to the r.f. measurements for sample imperfections, etc., would tend to increase the calculated conductivity above the quoted value. These results lend support to the notion that very high electrical conductivities are possible in the acceptor compounds of intercalated graphite and that the intercalated acid is responsible for a marked increase in the density of charge carriers while the mobility remains high.