First-principles study of mechanical and magnetic properties of transition metal (M) nitrides in the cubic M4N structure

Abstract We report results from systematic calculations performed by density functional theory on mechanical properties of twenty-eight 3 d, 4 d and 5 d transition metal (M) nitrides (TMNs) in metal-rich cubic M 4 N structure as novel candidates for hard coatings materials. We have computed lattice constants, elastic constants, derived moduli and ratios which characterize mechanical properties, and other properties like magnetic moments, formation energies, Debye temperature and Bader charge transfer. Our calculations indicate that all M 4 N-type metal nitrides except V 4 N, Nb 4 N, and Pt 4 N are mechanically stable. All Group 7 TMNs in the M 4 N structure are found to have high Vickers hardness values with the highest being 24.3 GPa for Re 4 N. Our computed lattice constants and magnetic dipole moments for Mn 4 N and Fe 4 N, the two compounds for which experimental measurements exist, are consistent with their measured values. Spin-polarized computations reduce the hardness of some magnetic compounds like Mn 4 N and Fe 4 N. The total density of states calculation reveals that all 28 M 4 N phases are metallic. The hybridization of metal d and nitrogen 2p orbitals is found to be the key factor in determining mechanical stability and hardness in these compounds. In contrast, ionicity, as computed by Bader charge transfer, does not correlate with hardness. Our comprehensive database for binary transition metal nitrides in M 4 N structure offers wide possibilities for experimental synthesis of such materials with desirable physical properties for the hard-coatings application.