Anisotropy of Graphite Intercalation Compounds
Graphite intercalation compounds consist of an alternating sequence of one or more hexagonal carbon layers separated by monolayers of intercalated atoms or molecules (1). The resulting compounds invariably exhibit metallic behavior parallel to the layers, with σa of order 105Ω-1cm-1 at the saturated limit of one intercalant layer per carbon layer. This behavior is essentially independent of intercalant species, although metallic intercalants such as Li, K, Rb, etc. give n-type conductivity whereas electron acceptor intercalants (Br2, HNO3, AsF5, etc.) lead to p-type conduction. A much greater variability is observed in properties perpendicular to the layers. Metallic intercalants lead to large σc, suggesting relatively mild overall anisotropy, while acceptor intercalation causes a strong reduction in σc and anisotropics (measured by σa/σc) as large as 106 at 300 K. This unusual and highly variable anisotropy is manifested not only in the crystallographic, electronic and mechanical properties, but also more subtly in the variation of critical phenomena among different compounds (2).
KeywordsLayer Spacing Graphite Layer Ionic Model Graphite Intercalation Compound Donor Compound
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