Coherency strains and staging in graphite intercalation compounds

Abstract

We examine an elastic mechanism for staging based on the domain model for graphite intercalation compounds first proposed by Daumas and Hérold. The attractive elastic interactions between intercalant atoms are shown to result in the formation of two-dimensional intercalant islands. The interaction energies of these islands are calculated as a function of island size and separation in a simplified strip geometry and related to the domain model. Because of these long range (range ∼ island size) coherency strains, the free energy of mixed or randomly staged crystals is greater than that of a pure stage intercalation compound. The implications of both the elastic and electronic interactions on the thermodynamics of intercalation (stage dependence of the equilibrium vapor pressure) are discussed. Experiments are suggested where the kinetics of the staging process are related to the microscopic interactions involved.