Anomalous electronic behaviour of Na superfullerides: Theory and experiment

Theory and experiment on NaxC60 agree that there is an anomalous trend as well as a limitation in the charge transfer from the sodiums to C-60, for x > 6. As revealed by both ab initio calculations and electron energy loss spectroscopy, the origin lies in the formation of interstitial states that trap a part of the excess electrons and that are neither C-60- nor sodium-derived. This may well be a general characteristic of heavily doped intercalated fullerides and other cluster-based solid compounds.