Reversible Pressure-Induced Amorphization in SolidC70: Raman and Photoluminescence Study

We have studied single crystals of ${\mathrm{C}}_{70}$ by Raman scattering and photoluminescence in the pressure range from 0 to 31.1 GPa. The Raman spectrum at 31.1 GPa shows only a broadband similar to that of the amorphous carbon without any trace of the Raman lines of ${\mathrm{C}}_{70}$. After releasing the pressure from 31.1 GPa, the Raman and the photoluminescence spectra of the recovered sample are that of the starting ${\mathrm{C}}_{70}$ crystal. These results indicate that the ${\mathrm{C}}_{70}$ molecules are stable up to 31.1 GPa and the amorphous carbon high pressure phase is reversible, in sharp contrast to the results on solid ${\mathrm{C}}_{60}$. A qualitative explanation is suggested in terms of intermolecular versus intramolecular interactions.