Cooperative effects and staging n graphite intercalation compounds

Abstract

A review is presented of some examples of cooperative phenomena in graphite intercalation compounds with an emphasis on the origin and role of staging. A phenomenological model of interactions between intercalant atoms is treated to yield phase diagrams as a function of stage, temperature, chemical potential, and concentration. The range of stoichiometries as a function of temperature and chemical potential is related to concurrent changes of stage. The cooperative behavior of the intercalant atoms is further studied in a calculation of the time dependence of the structure factor describing the instantaneous density distribution of intercalant. Upon quenching from a homogeneous, nonstoichiometric stage-1 phase, the intercalant atoms tend to cluster within the plane to form islands whose positions in different planes are correlated as a result of the interlayer interaction. The microscopic origin of these interlayer interactions is examined from the point of view of both elastic and electrostatic interactions. Collective effects in the distribution of charge donated to the graphite layers by the intercalants manifest themselves in the screening of the intercalant layers. The results of a quantum-mechanical, self-consistent model for the nonhomogeneous c-axis charge distribution are presented. The theoretical results are related to measurements of both the lattice and electronic structure of these materials.