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

Abstract

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 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.