Raman modes of the two-dimensional tetragonal polymeric phase of C60 under high pressure

The effect of high hydrostatic pressure, up to 12 GPa, on the phonon spectrum and the material stability of the two-dimensional (2D) tetragonal C-60 polymer have been studied by means of Raman spectroscopy in the frequency range 100-2000 cm(-1). A number of Raman modes appear in the spectrum for pressures above similar to1.4 GPa, whose intensities increase with pressure. The pressure coefficients of the majority of the phonon modes change gradually to lower values for pressures around 4.0 GPa. The deformation of the C-60 molecular cage along with the change of the material to a more isotropic state (as far as its elastic properties are concerned) resulting from the application of high pressure may be causing the observed effects in the Raman spectra. These effects are reversible upon pressure release and therefore the material is stable in the pressure region investigated. (C) 2001 American Institute of Physics.