Low-temperature specific heats of rubidium-graphite intercalation compounds

The low-temperature specific heats of graphite-rubidium intercalation compounds were measured using a conventional calorimetric method in the temperature range from 1.5-6 K. The specific heats consisted of the electronic and lattice specific heats as well as a specific-heat anomaly due to a dispersionless optical mode of lattice vibration involving rubidium atoms. The present as well as previous data for graphite-potassium and -cesium compounds can be explained in terms of the heterogeneous charge distribution along the $c$ axis of the compounds.