High-pressure phase transition inRb6C60

Abstract

High-pressure and high-temperature studies have been carried out on the alkali metal--intercalated fullerene system ${\text{Rb}}_{6}{\text{C}}_{60}$ by performing x-ray diffraction (XRD), x-ray absorption, and Raman spectroscopy measurements. All of these techniques allow the obtaining of complementary information on the high-pressure behavior and evolution of the studied system. In particular, the occurrence of a reversible transition has been clearly identified at around 35 GPa both at 600 K and at room temperature by XRD and Raman spectroscopy, respectively. The XRD data show that the high-pressure phase is compatible with a hexagonal unit-cell structure with $a=8.360(2)\text{ }\text{\AA{}}$ and $c=14.830(7)\text{ }\text{\AA{}}$ at 43 GPa and 600 K. In correspondence with such transition, the Raman spectra exhibit an abrupt change in the frequency of the normal vibrations. By coupling the information obtained with the different experimental techniques, we suggest that the high-pressure structural transition is accompanied by the formation of two-dimensional polymers of ${\text{C}}_{60}$.