Staging in Intercalated Graphites, Polymers and Fullerenes

Abstract

Intercalation compounds of graphite formed by the incorporation of alkali metals into the interlayer van der Waals gaps have been studied extensively and are now known to exhibit a number of ordered phases with a variety of interesting structural and electronic properties. The review articles by Dresselhaus and Dresselhaus [1], and a more recent review by Safran [2] summarize a large body of experimental and theoretical data on these systems. Over the last several years it has become increasingly apparent that there are related structural phenomena associated with alkali doping of many conjugated polymers (e.g. of polyacetylene, polyparaphenylenevinylene, and related polymers) and even of the alkali doped fullerenes. These are also examples of synthetic metals which can be obtained from a reference insulating state, and in the case of the fullerenes this process can even lead to a conducting phase with superconducting ground state. Structurally, the alkali doped polymers are known exhibit at least two types of ordering of the alkali ions into “channel structures” which break the symmetry of the undoped host polymers. Stoichiometric phases of AxC60 with x = 1,2,3,4, and 6 have already been observed, and there is some preliminary experimental evidence for additional ordered phases in this guest host system.