Phase transformations in amorphous fullerite C60 under high pressure and high temperature

•First phase transformations of amorphous fullerite С60 at HTHP have been investigated.•Study was conducted by neutron diffraction and Raman spectroscopy.•No crystalline polymerized phases were formed in amorphous fullerite at HTHP.•Amorphous fullerite transforms into amorphous-like or crystalline graphite.•A diagram of phase transitions of amorphous fullerite was constructed for the first time.

First phase transformations of amorphous fullerite C60 at high temperatures (up to 1800 K) and high pressures (up to 8 GPa) have been investigated and compared with the previous studies on the crystalline fullerite. The study was conducted using neutron diffraction and Raman spectroscopy. The amorphous fullerite was obtained by ball-milling. We have shown that under thermobaric treatment no crystallization of amorphous fullerite into С60 molecular modification is observed, and it transforms into amorphous-like or crystalline graphite. A kinetic diagram of phase transformation of amorphous fullerite in temperature–pressure coordinates was constructed for the first time. Unlike in crystalline fullerite, no crystalline polymerized phases were formed under thermobaric treatment on amorphous fullerite. We found that amorphous fullerite turned out to be less resistant to thermobaric treatment, and amorphous-like or crystalline graphite were formed at lower temperatures than in crystalline fullerite.