Intercalant ordering and lattice dynamics in stage-1 KHgC4

Neutron scattering methods were used to investigate intercalant ordering and phonon spectra in KHg${\mathrm{C}}_4$ at 297 and 12 K. Two coexisting phases, each three dimensionally ordered, were observed in a bulk sample, with 2 × 2 and $\sqrt{3}\times 2$ registry of the intercalant superlattices with respect to graphite. The phonon measurements show that out-of-plane Hg vibrations have lower frequencies than in-plane intercalant motions. Accurate measurement of the C-C bond distance indicates a smaller charge transfer to C layers in KHg${\mathrm{C}}_4$ than in $M{\mathrm{C}}_8 (M=\mathrm{K},\mathrm{R}\mathrm{b},\mathrm{C}\mathrm{s})$.