Effect of In-Plane Density on the Structural and Elastic Properties of Graphite Intercalation Compounds

Abstract

Dramatic differences in structure, elastic properties, and order-disorder temperatures are observed for stage-2 Li-graphite of different in-plane density, indicating the importance of long-range interactions in cohesive properties. Li${\mathrm{C}}_{12}$ is three-dimensionally ordered up to ∼ 500 K with $\sqrt{3}\times \sqrt{3}$ Li superlattice and $\mathrm{AA}$ graphite stacking, whereas Li${\mathrm{C}}_{18}$ is disordered at 300 K and has $\mathrm{AB}$ stacking. LO and LA ($00l$) phonon energies are 30% greater in the former, which can be understood in terms of electrostatic effects.