High-pressure behavior of CsC8 graphite intercalation compound:: Lattice structures and phase-transition mechanism

The high-pressure phase diagram of CsC8 graphite intercalation compound has been investigated at ambient temperature up to 32 GPa. Combining x-ray and neutron diffraction and Raman and x-ray absorption spectroscopies, we report that CsC8 when pressurized undergoes phase transitions around 2.0, 4.8, and 8 GPa. Possible candidate lattice structures and the transition mechanism involved are proposed. We show that the observed transitions involve structural rearrangements in the Cs subnetwork, while the distance between the graphitic layers is continuously reduced at least up to 8.9 GPa. Around 8 GPa, important modifications of signatures of the electronic structure measured by Raman and x-ray absorption spectroscopies evidence the onset of a transition which could imply a change of stage. Finally, we also provide the c-axis compressibility of CsC8 between 0 and 8.9 GPa.