The influence of boron and silicon on the phase transformations of fullerene C60 at high temperatures and pressure

Abstract

The effect of doping with two carbide-forming nonmetals - Si or B - (7 at. % each) on the phase transformations of crystalline C60 fullerene at a pressure of 8 GPa in the temperature range of 400–950 °C was studied using the X-ray diffraction method. Samples were synthesized from powders in a high pressure toroidal chamber, and X-ray examination was carried out at room temperature after rapid cooling. It has been shown that doping does not change the sequence of phase transformations of C60 fullerene as the temperature increases, the following phases are still observed: fcc phase - rhombohedral phase – disordered (amorphous) graphite. Boron reduces the formation temperature of disordered graphite, but silicon does not. This influence of carbide-forming non-metallic elements is fundamentally different from the influence of carbide-forming metals – Al and Fe, the addition of which increases the stability of fullerene molecules and increases the temperature of its transformation into disordered (amorphous) graphite by hundreds of degrees (P. A. Borisova, M. S. Blanter, V. V. Brazhkin, and V. P. Filonenko, Phase Transformations in C60 Fullerene with Iron and Aluminum at High Pressures and Temperatures, Bulletin of the Russian Academy of Sciences: Physics, 84 (2020) 851–856).