Positional and Orientational Correlations in the Graphite Intercalate C 24 Cs

An x-ray study of the Cs layers in ${\mathrm{C}}_{24}$Cs is presented. The Cs layer has a uniform 2-d liquidlike structure at 300 K not in registry with the graphite layers. A crossover to 3-d interlayer correlation is observed at 165 K. Single-crystal measurements show that the Cs layers rotate relative to the graphite $〈100〉$ directions. An orientational ordering between two positionally disordered phases occurs at 228 K and a new transition to a mixed registered phase at 50 K is reported.