We report a detailed experimental and theoretical study of the ${\mathrm{Rb}}_6{\mathrm{C}}_{60}$ and ${\mathrm{Cs}}_6{\mathrm{C}}_{60}$ systems under pressure. X-ray diffraction and x-ray absorption experiments have been coupled with ab initio calculations in order to understand the mechanisms taking place during the compression of these intercalated systems. The whole data set is consistent with a pressure-induced modification of the shape of the ${\mathrm{C}}_{60}$ molecule. This deformation constitutes an enhancement of the calculated distortion of the molecule in these intercalated compounds at ambient conditions, being equivalent to pulling the molecule through the three orthogonal axes pointing toward the bcc faces containing the alkali metals. Both experiments and calculations show that the pressure-induced deformation of the fullerene molecule is more important for Rb than it is for Cs intercalation.

• Received 20 July 2007

DOI:https://doi.org/10.1103/PhysRevB.77.035429