Temperature and pressure dependence of orientational disorder and bonding in Li2CsC60

The structural properties of the Li2CsC60 fulleride, which has been shown b efore to be face centred cubic with strong Li+-C interactions, were studied by synchrotron X-ray powder diffraction at both ambient and elevated press ures. We find no evidence for a monomer-->polymer phase transition, analogo us to that encountered in sodium intercalated fullerides, either on slow co oling to 150 K at ambient pressure or on the application of pressure to 6.1 4 GPa at ambient temperature, with the structure always remaining strictly face centred cubic. Analysis of the high-resolution diffraction data at ele vated temperatures shows again no evidence for a phase transition with only a small weakening of the Li+-C interaction. (C) 1999 Elsevier Science Ltd. All rights reserved.