Abstract
Graphite is a layer compound, and charge transfer complexes are formed between graphite and donor or acceptor materials. These complexes are named as graphite intercalation compounds, where the guest materials are inserted between graphite layers. The graphite intercalaction compounds are metallic with two-dimensionality. The experimental studies of low-temperature heat capacities are presented to show the electronic structures and lattice vibrations in these compounds. The electronic specific heat of alkali-metal-graphite intercalation compounds is explained in terms of the charge-transfer between graphite and alkali metal. The lattice specific heats have the Debye and Einstein terms of lattice vibrations. In the alkali-metal-hydrogen-graphite ternary compounds, which are obtained by hydrogen uptake in alkali metal-graphite intercalation compounds, electronic specific heat is reduced as the increase of hydrogen concentration. This means that hydrogen with strong electron affinity reduces the concentration of conduction electrons on graphite and alkali-metal. The lattice bivration is modified by the presence of hydrogen. The heat capacity investigation suggests two-dimensionality of the electronic structure and lattice vibrations of acceptor graphite intercalation compounds. Magnetic specific heat is discussed for transition-metal-chloride-intercalated graphite.
