Superconductive superhard phase of BC7: Predicted via ab initio calculations

We present a first-principles study on a phase of BC7 with Amm2 space-group symmetry (we call o-BC7), which is selected from more than a dozen of candidates via energetic, mechanical and dynamical stabilities within a wide pressure scale from 0 to at least 100 GPa. Our calculated results show that this structure is highly incompressible with large bulk and shear modulus of 388 GPa and 430 GPa, respectively, which is even higher than cubic BN. Further investigations revealed that the Vickers hardness (Hv ≈ 49.5 GPa) is higher than t-BC3 reported recently. And the superconducting critical temperature is calculated to be 38 K, which is comparable to that of MgB2.