Phase Transformations at High Pressures and Temperatures in Fullerenes with Metal Additives

The effect metal additives (7 at %) have оn phase transformations at pressures of 2 and 8 GPa in the temperature range of 500–1100°C in C60 and C70 fullerites is studied via Raman spectroscopy and neutron and X-ray diffraction. It is shown that carbide-forming elements, Fe and Al, strongly (by hundreds of degrees) raise the temperature of transformation of fullerenes into disorientated graphite, while non-carbide-forming element Ag does not have such an effect. The stabilization effect of crystalline fullerenes is explained using known data on the interaction between metal atoms and fullerene molecules, and compared to the processes of fulleride formation.