Pressure and temperature diagram of polymerized fullerite

We have systematically studied the temperature-pressure diagram of C-60 at pressures between 37 kbar and 80 kbar and from room temperature to 900 degrees 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 fee fullerite to an orthorhombic phase of polymerized C-60 chains that, at higher temperature, polymerize to two-dimensional C-60 polymers. Above 800 - 900 degrees C the C-60 cage collapses with formation of an sp(2) 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.