Planar Diffusive Motion of Alkali-Metal Intercalant Atoms in Graphite

The planar diffusive motion of alkali-metal atoms in the disordered phases of the compounds Rb${\mathrm{C}}_{24}$ and Cs${\mathrm{C}}_{24}$ has been studied for the first time by quasielastic neutron scattering. All neutron spectra show Lorentzian line profiles arising from liquidlike alkalimetal diffusion within graphite planes. The widths increase with temperature and show de Gennes narrowing at the peak of the intercalant structure factor. The results also show that Cs atoms diffuse faster than Rb atoms.