INVESTIGATION OF THE ELECTRONIC DISTRIBUTION IN THE OCTAHEDRAL SITES OF SOLID C-60 THROUGH THE 260-K ORIENTATIONAL PHASE-TRANSITION

We have investigated the electronic distribution in the octahedral sit es of solid C60 through the 260 K orientational phase transition using temperature-dependent positron lifetime measurements on single crysta ls. In addition to a gradual temperature-dependent change in positron lifetime, we observe a sharp discontinuity at 260 K, whose size is con sistent with that expected from the volume change at the transition. W e also examined bulk atmospheric contamination effects on solid C60. S amples exposed only to air show no detectable positron lifetime change , but a slight change is observed in samples exposed to both air and l ight.