Investigation of the electronic distribution in the octahedral sites of solid C60 through the 260 K orientational phase transition

We have investigated the electronic distribution in the octahedral sites of solid C60 through the 260 K orientational phase transition using temperature-dependent positron lifetime measurements on single crystals. In addition to a gradual temperature-dependent change in positron lifetime, we observe a sharp discontinuity at 260 K, whose size is consistent with that expected from the volume change at the transition. We also examined bulk atmospheric contamination effects on solid C60. Samples exposed only to air show no detectable positron lifetime change, but a slight change is observed in samples exposed to both air and light.