High-pressure-induced metastable phase in tetragonal 2D polymeric C60

The structural stability of the tetragonal two-dimensional (2D) polymeric phase of C60 has been studied under pressure up to ∼24 GPa and room temperature by means of in situ Raman scattering. An irreversible transformation of the material to a new phase was observed at pressure ∼20 GPa. The phonon spectrum of the high-pressure phase provides a strong indication that the fullerene molecular cage is retained and therefore this phase may be related to a three-dimensional (3D) network of C60 cages. The new phase remains stable upon slow release of pressure to ambient conditions. The recovered material is metastable and transforms in air by detonation under laser irradiation to partially dimerized C60.