High-Pressure Phase in Tetragonal Two-Dimensional Polymeric C60

The pressure behavior of the phonon modes of tetragonal two-dimensional polymeric C60 has been studied at pressure up to 27.5 GPa and room temperature 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 spectrum characteristics of the high-pressure phase provide a strong indication that the fullerene molecular cage is retained and the material may be related to a three-dimensionally polymerized C60. The new phase remains stable upon pressure decrease down to 9 GPa. Further release of pressure leads to its transformation to a highly disordered structure whose broad features in the Raman spectrum resemble those of amorphous carbon.