Structural transitions of SWNT filled with C_(60) under high pressure

Raman spectra of C₆₀ filled single-walled carbon nanotubes (C₆₀@SWNTs) with diameters of 1.3-1.5 nm have been studied under high pressure. A plateau in the pressure dependence of the G-band frequency at around 10 GPa was observed in both experiments with 514 nm and 830 nm excitation lasers, which is similar to the high pressure behaviors of pristine SWNTs. This structural transition has been assigned to the transformation into a peanut-like structure of the nanotubes. At pressure below 2 GPa, no obvious Raman signature related to the structural transition of nanotubes was observed, unlike what has been reported for C₇₀ filled nanotubes. We discussed this point in terms of the arrangement differences of C₆₀ and C₇₀ molecules inside the nanotubes. At higher pressure up to 15 GPa, a graphite-like pressure evolution was observed in our C₆₀@SWNTs.