PHASE-TRANSFORMATIONS IN CARBON FULLERENES AT HIGH SHOCK PRESSURES

C60 powders were shock-compressed quasi-isentropically and quenched from pressures in the range 10 to 110 GPa (0.1 to 1.1 Mbar). Recovered specimens were analyzed by Raman spectroscopy and optical microscopy. C60 fullerenes are stable into the 13- to 17-GPa pressure range. The onset of a fast (approximately 0.5-mu-s) reconstructive transformation to graphite occurs near 17 GPa. The graphite recovered from 27 GPa and about 600-degrees-C is relatively well ordered with crystal planar domain size of about 100 angstrom. Above 50 GPa a continuous transformation to an amorphous state is observed in recovered specimens. The fast transformation to graphite is proposed to occur by pi-electron rehybridization which initiates breakup of the ball structure and formation of the graphite structure at high density.