Phonon-Raman Anomaly in the Ternary Graphite Intercalation CompoundK1−xRbxC8

Abstract

We report the first measurements of the Raman spectra of an alkali ternary-solid-solution graphite-intercalation compound ${\mathrm{K}}_{1\ensuremath{-}x}{\mathrm{Rb}}_{x}{\mathrm{C}}_{8}$, $0<~x<~1$. A broad asymmetric softening of the graphite $M$-point phonon modes is observed at $x\ensuremath{\approx}0.67$. This anomaly is attributed to electronic band-structure modifications which alter the electron-phonon contribution to the phonon self-energies and which result from the formation of K${\mathrm{Rb}}_{2}$-like clusters.