Phonons in Graphite Intercalation Compounds Measured by Neutron Scattering

Abstract

The entire phonon dispersion of a solid can be measured by neutron scattering under favorable conditions. In particular, triple axis spectroscopy allows the phonon energies to be determined for a chosen polarization at well defined wave vectors q throughout the Brillouin zone (BZ). For an unambiguous assignment of the excitations, single crystals have to be available. However, in the case of graphite a complete measurement of the phonon dispersion is not possible because of the limited size of (natural) single crystals, and because of the high energy (∼ 200 meV) of some branches. Therefore, only a limited amount of neutron data have been collected with pyrolytic graphite (PG) [1,2]. Together with q = 0 modes from light scattering techniques [3], they have been used to calculate the whole phonon dispersion of graphite [2,4]. It now serves as a guide for the discussion of the phonon dispersion of graphite intercalation compounds (GIC).