IrN and IrN as potential high-energy-density materials.

Transition metal nitrides have attracted great interest due to their unique crystal structures and applications. Here, we predict two N-rich iridium nitrides (IrN and IrN) under moderate pressure through first-principles swarm-intelligence structural searches. The two new compounds are composed of stable IrN octahedrons and interlinked with high energy polynitrogens (planar N or cyclo-N). Balanced structural robustness and energy content result in IrN and IrN being dynamically stable under ambient conditions and potentially as high energy density materials. The calculated energy densities for IrN and IrN are 1.3 kJ/g and 1.4 kJ/g, respectively, comparable to other transition metal nitrides. In addition, IrN is predicted to have good tensile (40.2 GPa) and shear strengths (33.2 GPa), as well as adequate hardness (20 GPa). Moderate pressure for synthesis and ambient pressure recoverability encourage experimental realization of these two compounds in near future.