Prediction of Molybdenum Nitride from First-Principle Calculations: Crystal Structures, Electronic Properties, and Hardness

Transition metal (TM) nitrides has been widely used in many scientific and technical areas because of their unique physical and mechanical properties. However, most of the well-known transition metal nitrides are nitrogen deficient. The reports on nitrogen-rich TM nitrides are rather scarce and sometimes even show discrepancy in their crystal structures. Herein, the microstructure, stability, electronic property, and hardness of nitrogen-rich molybdenum nitride MoN2 compound have been investigated systematically by using an unbiased structure search method crystal structure analysis by particle swarm optimization combined with first-principle calculations. Our study demonstrates a stable configuration orthorhombic Cmc21 (no. 36) for MoN2 crystal, which is even lower in energy than the experimental synthesized structure rhombohedral R3m-MoN2 at ambient pressure condition. The formation enthalpies with respect to the reactant Mo + N2, mechanical stabilities, and phonon dispersions further confirm the stability of Cmc21-MoN2 phase at the whole ambient condition, indicating that it can be synthesized in experiment. According to the density of states, it is seen that all the considered MoN2 exhibit metallic behavior and have two types of bonds (covalent and ionic). The Vicker hardness of Cmc21-MoN2 is calculated as 11.987 GPa, and the strength and number of covalent bonds may dominate its hardness.