X-Ray Diffraction Studies on C60 under High Pressure

In situ high pressure X-ray diffraction experiments have been done for super-pure C60 powder sample using synchrotron radiation X-ray source and an energy dispersion detector. The pressure is generated by DAC. Pt was used as an inner pressure standard, whose EOS is known. The pressure of the sample was determined by the diffraction data of Pt. The maximum experimental pressure is 30 GPa. The results indicate that crystal C60 has a fcc structure with lattice parameter a=1.420 86 nm at ambient condition; and the crystal structure of C60 was changed under high pressure. A lower symmetry phase reached at 13.7 GPa, marked by the splitting of broaden continuously and their intensities became very week. The background raised obviously at about 25 GPa, it showed that C60 crystal began to transform to an amorphous state. The diffraction lines disappeared wholly, thus the transformation to amorphous state was finished completely at about 30 GPa. We also carried out X-ray diffraction experiments for C60 samples quenched at various pressure up to 44 GPa. The samples were in non-hydrostatic pressures. The spectra showed that crystal C60 transformed to amorphous state beyond 30 GPa. Finally, the phenomena of pressure-induced transition from crystal to amorphous state are discussed.