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

摘要

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 Re _(0.5)Ir_(0.5)B_2, Re_(0.5)Tc _(0.5)B_2, Os_(0.5)W_(0.5)B_2 and Os_(0.5)Ru_(0.5)B_2. The elastic moduli decrease from pure metal diboride ReB_2 to Re_(0.5)Ir_(0.5)B _2 and on the contrary increase from OsB_2 to Os _(0.5)W_(0.5)B_2 because boron-metal interactions are contaminated by the occupied anti-bonding orbitals. Alloying ReB_2 (OsB_2) 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.