Theory of Pressure-Induced Staging Transitions in Graphite Intercalation Compounds

Theory is presented of the mechanism of pressure-induced staging transitions in alkali-metal graphite intercalation compounds (A-GIC's). The most stable stoichiometry at T =0 K is determined for various species of intercalant atoms. Effect of pressure is taken into account by varying the distance between the two graphite layers which sandwich an intercalant layer. Lithium GIC's are found to be stable with the stoichiometry of LiC 6 × n , where n is the stage number, at all pressures. The most stable stoichiometry of heavy alkali-metal GIC's is shown to be MC 14 × n at ambient pressure, but MC 8 × n at higher hydrostatic pressure. Comparison is made of the theoretical results with the experimental ones at finite temperatures.