Predicting hard metallic osmium–carbon compounds under high pressure

By using particle-swarm optimization technique, we have designed three potential hard osmium carbides OsC2, OsC3 and OsC4. All compounds have novel sp3sp3-bonded carbon motif sandwiched with osmium layer. The mechanical properties have significantly improved with the increasing of C percentage, in view of the increased ratio of the shear/bulk modulus, from 0.48 in OsC2 to 0.74 in OsC4. Especially, the Vickers hardness of OsC4 was calculated to be 37 GPa, exceeding the hardness (31.8 GPa) of WB4. Electronic results reveal that the strong covalent OsC and CC bonds are the driving force for the high hardness of these carbides.

► We have designed three hard osmium carbides by first principle calculations.
► Increasing C percentage can significantly improve the mechanical properties.
► The Vickers hardness of osmium carbides has been calculated.
► The origin of the high hardness of osmium carbides was studied.