Pressure and temperature diagram of polymerized fullerite

We have systematically studied the temperature-pressure diagram of C₆₀ at pressures between 37 kbar and 80 kbar and from room temperature to 900 ^∘{}C. We show here the specific role played by the temperature in the phase transformations observed in the P-T region covered by this study. As temperature is increased, we follow the continuous transformation of fcc fullerite to an orthorhombic phase of polymerized C₆₀ chains that, at higher temperature, polymerize to two-dimensional C₆₀ polymers. Above 800 -900 ^∘{}C the C₆₀ cage collapses with formation of an sp² amorphous phase. The continuous evolution of the x-ray patterns during these phase transformations is explained on the basis of a homogeneous solid-state polymerization.