Gap reduction and the collapse of solidC60to a new phase of carbon under pressure

Abstract

We have studied solid ${\mathrm{C}}_{60}$, measuring the shift of the optical absorption edge with pressure to 35 GPa. In the range of 0–17 GPa, extrapolation of the absorption edge indicates that metallization should occur by 33 GPa. However, from 17 to 25 GPa an irreversible transition to a ‘‘transparent phase’’ occurs. Raman scattering of the depressurized sample shows no trace of ${\mathrm{C}}_{60}$, diamond, or graphite, indicating that the transition involves the collapse of the ${\mathrm{C}}_{60}$ molcules into a new structure of carbon.