Temperature and pressure dependence of orientational disorder and bonding in Li₂CsC₆₀

The structural properties of the Li₂CsC₆₀ fulleride, which has been shown before to be face centred cubic with strong Li⁺-C interactions, were studied by synchrotron X-ray powder diffraction at both ambient and elevated pressures. We find no evidence for a monomer→polymer phase transition, analogous to that encountered in sodium intercalated fullerides, either on slow cooling to 150 K at ambient pressure or on the application of pressure to 6.14 GPa at ambient temperature, with the structure always remaining strictly face centred cubic. Analysis of the high-resolution diffraction data at elevated temperatures shows again no evidence for a phase transition with only a small weakening of the Li⁺-C interaction.