High-pressure phase in tetragonal two-dimensional polymeric C-60

The pressure behavior of the phonon modes of tetragonal two-dimensional pol ymeric C-60 has been studied at pressure up to 27.5 GPa and room temperatur e by means of Raman spectroscopy. Gradual transformation of the material to a new phase was observed in the pressure region 18.0-22.0 GPa. The Raman s pectrum characteristics of the high-pressure phase provide a strong indicat ion that the fullerene molecular cage is retained and the material map be r elated to a three-dimensionally polymerized C-60. The new phase remains sta ble upon pressure decrease down to 9 GPa. Further release of pressure leads to its transformation to a highly disordered structure whose broad feature s in the Raman spectrum resemble those of amorphous carbon.