HIGH-PRESSURE TRANSFORMATIONS OF C-60 TO DIAMOND AND SP(3) PHASES AT ROOM-TEMPERATURE AND TO SP(2) PHASES AT HIGH-TEMPERATURE

Although stable under hydrostatic pressures up to 20 GPa, C60 molecules transform to a transparent and insulating material if compressed nonhydrostatically at room temperature. On the other hand, quasihydrostatic loading at higher temperatures yields black, electrically conducting samples. We report here on detailed x-ray synchrotron-radiation and electron-diffraction characterization of these samples. The former transparent samples consist in polycrystalline cubic diamond embedded in a bulk sp3 amorphous matrix, while the latter samples correspond to a graphitic amorphous sp2 structure.