Structural stability and mechanical properties of Ni_xMo_yN ternary nitrides under high pressure: A first-principles study

Transition metal nitrides have attracted significant attention due to their outstanding properties; however, studies on ternary systems under high pressure remain limited. In this work, we systematically investigated the structures and properties of NiMoN compounds in the pressure range of 0–100 GPa by combining crystal structure analysis by particle swarm optimization (CALYPSO) structure prediction with first-principles calculations. To explore more structural possibilities, a large number of candidate structures were predicted and those with potential stability were selected. Among the newly predicted structures, a stable phase P2₁3-NiMo₄N and a low-energy metastable phase I4₁32-NiMo₃N are proposed for the first time. The metastable structure I4₁32-NiMo₃N lies 0.007 eV/atom above the convex hull, whereas the energy of the experimentally synthesized structure Fd3m-Ni₃Mo₃N is 0.036 eV/atom above the convex hull. Therefore, I4₁32-NiMo₃N can likely be obtained through experimental synthesis. Phonon and elastic constant calculations confirm the stability of P2₁3-NiMo₄N and I4₁32-NiMo₃N, while electronic structure calculations indicate that both exhibit metallic behavior, with Mo-4d orbitals making the primary contribution at the Fermi level. Mechanical property evaluations reveal that P2₁3-NiMo₄N exhibits high hardness, whereas I4₁32-NiMo₃N shows relatively lower hardness but enhanced ductility. Under different pressures, both structures exhibit comparable ideal tensile strengths, but their failure mechanisms differ. This study broadens the known structural diversity of NiMoN ternary nitrides and provides theoretical insights into the exploration of high-pressure ternary nitrides.