Mechanical and electronic properties of 5d transition metal diborides M[B.sub.2] (M=Re, W, Os, Ru)

First-principles method is used to assess the structural, mechanical, and electronic properties of 5d transition metal diborides M[B.sub.2] (M=Re, W, Os, Ru). The high modulus, large strength, and high hardness exhibited by the 5d transition metal diborides is attributed to the presence of strong directional covalent B-B and M-B bonds in the electronic structures of the materials.