Anisotropy of the elastic properties and the microhardness of disordered superhard carbon obtained from C$_{60}$ fullerite under high pressures

An anisotropy of the propagation velocities of longitudinal and transverse ultrasonic waves, as well as of the microhardness, is observed for disordered graphite-like samples obtained from C$_{60}$ fullerite by heating to different temperatures between $1000$ and $1300^\circ$C under a pressure of $7.5$ GPa. The anisotropy of the elastic properties and the microhardness is attributed to the additional pressure component that occurs in the quasi-hydrostatic experimental conditions. The elastic characteristics of the samples are determined with allowance for the uniaxial orientational anisotropy. A model description relating the observed properties of superhard $sp^2$ carbon to its possible structural features and to the mechanism of its formation is proposed.