Interlayer interactions in LiC6: Compressibility and thermal expansion.

Abstract

Interlayer interactions in the prototype stage-1 graphite intercalation compound LiC{sub 6} are probed by neutron diffraction measurements of {ital c}-axis compressibility {kappa}{sub {ital c}} at 300 K and {ital c}-axis thermal expansion {alpha}{sub {ital c}} in the interval 300{endash}700 K. We find a constant {kappa}{sub {ital c}}=1.43{plus_minus}0.02{times}10{sup {minus}12} cm{sup 2}/dyn for hydrostatic pressures {le} 23 kbar, about half that of graphite. In contrast, {alpha}{sub {ital c}}= 59{times}10{sup {minus}6}/K, twice that of graphite. Estimates of effective {ital c}-axis Gr{umlt u}neisen parameters show that the interlayer potential in LiC{sub 6} is in fact considerably more anharmonic than that of graphite. Measurements of {alpha}{sub {ital c}} on high temperature stage-1 solid solutions suggest even greater anharmonicity when 30{percent} of the Li sites are vacant. {copyright} {ital 1996 The American Physical Society.}