Electronic bonding analyses and mechanical strengths of incompressible tetragonal transition metal dinitrides TMN(2) (TM = Ti, Zr, and Hf)

Motivated by recent successful synthesis of transition metal dinitride TiN(2), the electronic structure and mechanical properties of the discovered TiN(2) and other two family members (ZrN(2) and HfN(2)) have been thus fully investigated by using first-principles calculations to explore the possibilities and provide guidance for future experimental efforts. The incompressible nature of these tetragonal TMN(2) (TM = Ti, Zr, and Hf) compounds has been demonstrated by the calculated elastic moduli, originating from the strong N-N covalent bonds that connect the TMN(8) units. However, as compared with traditional fcc transition metal mononitride (TMN), the TMN(2) possess a larger elastic anisotropy may impose certain limitations on possible applications. Further mechanical strength calculations show that tetragonal TMN(2) exhibits a strong resistance against (100)[010] shear deformation prevents the indenter from making a deep imprint, whereas the peak stress values (below 12 GPa) of TMN(2) along [Image: see text]shear directions are much lower than those of TMN, showing their lower shear resistances than these known hard wear-resistant materials. The shear deformation of TMN(2) at the atomic level during shear deformation can be attributed to the collapse of TMN(8) units with breaking of TM-N bonds through the bonding evolution and electronic localization analyses.