Electronic structure, phase stability, and hardness of the osmium borides, carbides, nitrides, and oxides: First-principles calculations

The chemical bonding, elastic behavior, phase stability, and hardness of OsB, OsB2, OsC, OsO2, OsN, and OsN2 have been systematically studied using first-principles calculations. The calculation suggests that the chemical bonding in these compounds is a mixture of covalent and ionic components. The structural stability of OsB, OsC, and OsN can be understood in terms of the band filling of the bonding states, and the results indicate that the hexagonal tungsten carbide structure is more stable. The hardness of these osmium compounds is calculated using both ab initio and semiempirical model calculations. Analysis of the ab initio hardness suggested that the large occupations and high strength of the covalent bonds are crucial for a superhard material, and there is no clear connection between bulk modulus and hardness in these osmium compounds.