Elastic properties of ultrahard fullerites

The elastic properties of C-60 fullerite samples synthesized under pressure P = 13.0 GPa at high temperatures were investigated using acoustic microsc opy. The velocities of longitudinal (c(L) = 17-26 km/s) and transverse (c(T )=7.2-9.6 km/s) elastic waves in the samples were measured. It was establis hed that the longitudinal sound velocity of ultrahard fullerites is higher than that of any other known solid. The bulk modulus of these ultrahard sam ples is higher than that of diamond and reaches a value greater than 1 TPa. The high bulk modulus, the relatively large shear moduli, and the substant ial Poisson ratio indicate that the structure of the ultrahard fullerites i s fundamentally different from that of diamond. (C) 1998 American Institute of Physics. [S1063-7761(98)01410-3].