‘Low-pressure’ orthorhombic phase formed from pressure-treated C60

X-ray and electron diffraction and Raman spectroscopy have shown that the solid formed by a pressure-temperature treatment of C60 at 1.5 GPa-723 K has an orthorhombic structure O′. It may be considered that phases O′ and O, the previously known orthorhombic phase formed at 8 GPa-573 K, are the same so that our pressure-temperature treatment provides “the optimal way of obtaining the linear-chain orthorhombic fullerene phase”. However, differences in the respective spectra of these two phases led us to re-examine the structure of the previously described phase O: it is found that a rhombohedral structure fits the experimental X-ray data at least as well as an orthorhombic one does. In any case, phase O′ may be an intermediary for the formation of the tetragonal high-pressure modification.