PRESSURE-INDUCED TRANSFORMATIONS AND OPTICAL PROPERTIES OF THE TWO-DIMENSIONAL TETRAGONAL POLYMER OF C₆₀ AT PRESSURES UP TO 30 GPa
Meletov K.P., Arvanitidis J., Assimopoulos S., Kourouklis G.A., Sundqvist B.

Received: April 24, 2002

PACS: 61.48.+c, 62.50.+p, 64.70.Kb, 78.30.Na, 78.55.Kz

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The Raman spectra of the two-dimensional tetragonal (2D(T)) polymeric phase of C₆₀ have been studied in-situ at pressures up to 30 GPa and room temperature. The pressure dependence of the phonon modes shows an irreversible transformation of the material near 20 GPa into a new phase, most probably associated with the covalent bonding between the 2D polymeric sheets. The Raman spectrum of the high-pressure phase is intense and well-resolved and the majority of modes are related to the fullerene molecular cage. The sample recovered at ambient conditions is in a metastable phase and transforms violently under laser irradiation: the transformed material contains mainly dimers and monomers of C₆₀ and small inclusions of the diamond-like carbon phase. The photoluminescence spectra of the 2D(T) polymer of C₆₀ were measured at room temperature and pressure up to 4 GPa. The intensity distribution and the pressure-induced shift of the photoluminescence spectrum drastically differ from those of the C₆₀ monomer. The deformation potential and the Grüneisen parameters of the 2D(T) polymeric phase of C₆₀ have been determined and compared with those of the pristine material.