Is Rhenium Diboride A Superhard Material?

摘要

Superhard materials are usually composed of light elements such as boron, carbon, nitrogen, and oxygen. These light elemental atoms have the ability to form covalently bonded, three-dimensional networks of high atomic density with extreme resistance to external shear. Most researchers agree on the definition according to which "superhard" materials are those with Vickers hardness (Hv) higher than 40 GPa such as diamond, cubic boron nitride (cBN), B_6O, and BC_2N. The search for new superhard materials beyond B-C-N-O system has been extensively undertaken during recent years such as transition-metal borides, carbides, nitrides, or oxides. Since, Os has the highest valence-electron density and the least compressibility among the transition metals, it is natural that OsB_2 becomes one typical example and has been systematically studied recently.