Lattice vibrations in graphite and intercalation compounds of graphite

The lattice modes of pure graphite can be divided into intraplanar displacements and interplanar displacements. Upon intercalation, the intraplanar vibration frequencies are only slightly shifted, though their Raman and infrared intensities can be greatly changed. These characteristics of the intraplanar vibrational modes are interpreted in terms of symmetry changes associated with intercalation. These symmetry changes give rise to both inplane and c-axis zone folding effects. Detailed results are reported for the Raman spectra of graphite-halogen acceptor compounds and graphite-alkali metal donor compounds. In the case of the graphite-halogen compounds, spectra showing both graphitic modes and intercalate modes are interpreted in terms of this symmetry model. In the case of the alkali metal compounds, the spectra for stage 1 compounds are considered separately from those for higher stage compounds. Particular attention is given both to the broad asymmetric Breit-Wigner high frequency structure and to the sharp doublet structure observed at intermediate frequencies. Infrared spectra of lattice modes in graphite intercalation compounds are reported.