Prediction of a superhard material of ReN₄ with a high shear modulus

Using first-principles calculations, this paper systematically investigates the structural, elastic, and electronic properties of ReN₄. The calculated positive eigenvalues of the elastic constant matrix show that the orthorhombic Pbca structure of ReN₄ is elastically stable. The calculated band structure indicates that ReN₄ is metallic. Compared with the synthesized superhard material WB₄, it finds that ReN₄ exhibits larger bulk and shear moduli as well as a smaller Poisson's ratio. In addition, the elastic constant c_44 of ReN₄ is larger than all the known 5d transition metal nitrides and borides. This combination of properties makes it an ideal candidate for a superhard material.