The work done at the University of Pennsylvania was supported by the National Science Foundation MRL Program under Grant No. DMR91-20668, by NSF Grant No. DMR-91-22784, and by the Department of Energy, DE-FC02-86ER45254 and DE-FG05-90ER75596. The SUNY X3 beamline is supported by the Division of Basic Energy Sciences of the U.S. Department of Energy under Grant No. DE-FG-0291-ER45231. The Brookhaven NSLS is supported by DOE, Division of Materials Sciences, DEAC02-76CH00016.
Physical Review Letters
X-ray diffraction, Calorimetry, Fullerenes -- Electric properties, Coulomb excitation -- Statistical methods
X-ray diffraction and calorimetry data on cubic NaxC60(1<x60, e.g., Tm(x=1.3)=325 K. The ordered phases are the same as in pure C60: simple cubic, space group Pa3¯, but the orientations in the disordered phase are more restricted. We explain how Na stabilizes the ordered phase to rather high T, while K and Rb do not, in terms of Coulomb interactions between C60 molecules and and Na ions which we calculate from the local charge density of C60.
Yildirim, T. and Fischer, J. E. and Harris, A. B. and Stephens, P. W. and Liu, D. and Brard, L. and Strongin, R. M. and Smith, A. B. (1993). Orientational phase transition in NaxC60 (1