LAUSR

Abstract Three novel orthorhombic carbon crystals were designed and their stability, sound velocities, thermal conductivity and dynamically and mechanical properties were investigated. Density functional theory calculations show that the three carbon crystals are energetically stable with cohesive energies less than −8.94 eV and their elastic constants satisfy the mechanical stability criterion of orthorhombic system. They are anisotropic superhard materials with Vickers hardness of over 79 GPa based on four different models. Their Debye temperature are over 2100 K, only a little lower than that of diamond. The calculations show that they may be synthesized from cold-compressed graphite under pressure of less than 20 GPa. Their similar structural features to diamond and excellent mechanical performance suggest that diamond can be a useful structural template of superhard materials.