Electronegativity Identification of Novel Superhard Materials

We show that electronegativity can be used to effectively identify the hardness of crystal materials on the basis of a new microscopic model for hardness. Bond electronegativity is proposed to characterize the electron-holding energy of a bond, which is the intrinsic origin of hardness. Applying this model to c-BC₂N materials, we confirm the proper bond composition of the experimentally observed phase of c-BC₂N, in which the bond ratio $N(C{{{-}}}C){:}N(B{{{-}}}N){:}N(B{{{-}}}C){:}N(C{{{-}}}N)$ is $3{:}3{:}1{:}1$. A number of bonds that can or cannot form a superhard material are qualitatively distinguished, which enables us to explore novel superhard materials by screening possible elemental combinations.