N structure*

We report results from systematic calculations performed by density functional theory [1] on mechanical properties of twenty-eight 3d, 4d and 5d transition metal (M) nitrides (TMNs) in metal-rich cubic M4N structure as novel candidates for hard coatings materials. Our calculations indicate that all M4N-type metal nitrides except V4N, Nb4N, and Pt4N are mechanically stable. All Group 7 TMNs in the M4N structure are found to have high Vickers hardness values with the highest being 24.3 GPa for Re4N. Our computed lattice constants and magnetic dipole moments for Mn4N and Fe4N are consistent with their measured values. Spin-polarized computations reduce the hardness of some magnetic compounds like Mn4N and Fe4N. The hybridization of metal d and nitrogen 2p orbitals is found to be the key factor in determining mechanical stability and hardness. The database for binary transition metal nitrides in M4N structure offers possibilities for experimental synthesis for the hard-coatings application.

[1] V. Adhikari, Z. T. Y. Liu et. al, JPCS, 120, 197, 2018; https://doi.org/10.1016/j.jpcs.2018.04.043.