Lattice Dynamics of Pyrolytic Graphite

The frequencies of certain normal modes of vibration of the graphite lattice have been studied on samples of high-quality pyrolytic graphite by coherent, inelastic-neutron-scattering techniques. Some of the data are not compatible with certain restrictions imposed by the valence-bond model as presented by Young and Koppel. Therefore, the data have been analyzed in terms of a simple axially symmetric, Born-von K\'arm\'an force-constant model. The results show that appreciable interactions exist between third nearest neighbors in the basal plane. The force model has been used to calculate a frequency distributio function and the lattice specific heat of graphite. These calculations are in excellent agreement with the specific heat measured for natural graphite in the temperature range 1.5-300\ifmmode^\circ\else\textdegree\fi{}K.