Mixed-metal effects on ultra-incompressible metal diborides: Density functional computations

Mixed-metal borides are promising superhard materials (Kaner et al. (2005) [1]). In this Letter, density functional computations have been applied to the structural, electronic and elastic properties of mixed-metal diborides Re0.5Ir0.5B2, Re0.5Tc0.5B2, Os0.5W0.5B2 and Os0.5Ru0.5B2. The elastic moduli decrease from pure metal diboride ReB2 to Re0.5Ir0.5B2 and on the contrary increase from OsB2 to Os0.5W0.5B2 because boron–metal interactions are contaminated by the occupied anti-bonding orbitals. Alloying ReB2 (OsB2) with Tc (Ru) decreases the elastic moduli owing to the relativistic effects. Mixed-metal effects on elastic deformations focus on bonding strengths, which effectively tune the elastic properties of metal diborides.