THE DYNAMIC STRUCTURE FACTOR OF LIC6 AND KC8 - INELASTIC SYNCHROTRON X-RAY-SCATTERING RESULTS

The dynamic structure factor S(q, omega) of electrons in lithium-intercalated graphite (LiC6) and potassium-intercalated graphite (KC8) for momentum transfer q parallel-to c-axis has been measured by inelastic synchrotron X-ray scattering. The dielectric function epsilon(q, omega) was deduced from the data and compared with epsilon(q, omega) of pristine graphite. The main feature in the different Im [epsilon(q, omega)]-spectra, a more or less intense peak around 14 eV, can be assigned to maxima of the symmetry-projected joint density of occupied and unoccupied electron states near the Fermi level. Knowing the position of the occupied bands by photoemission experiments, predictions about the unoccupied pi and interlayer states can be made. In the case of LiC6, a shift and broadening of the first Im [epsilon(q, omega)]-peak was found, which can be explained by a decrease of the energy of the interlayer-band because of the strong hybridization of this graphite-derived band with the Li metal 2 s-band. In the case of KC8, a weakening of the first peak of Im [epsilon(q, omega)] was observed, which we attribute both to a decreasing overlap of the occupied pi-derived state with the empty interlayer state and to a change of symmetry of the occupied sigma-derived states as well as of the empty pi-derived states.