Superhard polymorphs of diamond-like BC7

Using particle swarm optimization (PSO) methodology for crystal structure prediction, we have found four potential superhard structures of P-4m2, P3m1, Pmm2 and R3m, energetically much superior to the previously proposed P-43m structure. Our density functional calculation not only confirmed these simulated structures to be superhard materials (>40 GPa), but also reveal that they exhibit metallic behavior. Further phonon and elastic constants calculations imply these structures are all mechanically stable. Therefore, they have good prospects for electronic applications as superhard materials under high pressure.

Research highlights
► This paper systematically studied the crystal structures of BC7 in theory.
► We have studied the mechanical properties and electronic structure of BC7.
► Our calculation results reveal that d- BC7 is a superhard material.