Properties and Applications of Superhard and Ultrahard Fullerites

Synthesis conditions, structures and physical properties of superhard and ultrahard forms of carbon obtained from C 60 fullerene by static high-pressure-high-temeperature treatment are presented. The unit-cell parameters and intermolecular bonds have been found using molecular mechanics calculations and X-ray diffraction profile analysis. A weighted pattern factor R wp of 5–10% has been achieved when besides (2+2) intermolecular bonds a ‘common 4-memeber ring’ and (3+3) type links are considered. The sound velocities have been measured and a full set of elastic moduli calculated. The highest value of longitudinal sound wave velocity 26±2 km s −1 has been found which is a record value for known solids. The bulk elastic modulus and the hardness of ultrahard fullerites are higher than the values for diamond. The correct diamond hardness at room temperature has been measured using the ultrahard fullerite indentors.