Cluster structure and elastic properties of superhard and ultrahard fullerites

摘要

Velocities of the longitudinal and shear sound waves are measured in ultrahard fullerites created by static high-pressure-high-temperature treatment under P=13 GPa and T= 1670-1870 K. The highest value of 26.0 km/s for the longitudinal waves is measured, that is about 40% more than in diamond. Bulk modulus of different ultrahard fullerites covers the range of about 600 -1700 GPa. The highest hardness is about 30 × 10~3 kg/mm~2. We ascribe these unique properties to formation of 20-30 atoms clusters by the walls of adjacent molecules under process of 3D-cross-linking. Most distinctly these clusters declare themselves in the cubic structure with the lattice parameter about 6 A and 32 atoms per unit cell.