Mechanical properties of superhard BC5

We apply density functional theory concept to investigate mechanical properties of the diamondlike compound BC5. The cell volume and the bulk modulus are in very good agreement with the experiment, confirming the claimed crystal structure of BC5. The cleavage properties revealed a very strong cohesion between B–C bonded planes, which is comparable to C–C bonded planes. The lowest cleavage stress, which can be related to hardness, is 83 GPa. The critical shear stresses are 83 and 108 GPa, respectively, for B–C and C–C planes. This difference of critical stresses corresponds well to the difference in Vickers hardness between BC5 and diamond.