Lanthanium nitride LaN 9 featuring azide units: the first metal nine-nitride as a high-energy-density material

High-pressure phase diagrams of the La-N binary system were systematically constructed using the CALYPSO method and first-principles calculations. In addition to the pressure-induced La-N compounds reported previously, we have uncovered a hitherto unknown LaN structure in 3̄ symmetry stabilized within a narrow pressure range of 20-24.5 GPa. Notably, LaN stands as the first thermodynamically stable metal nine-nitrogen compound, featuring centrosymmetric linear N anion units and an edge-sharing LaN icosahedron. Charge transfer between the La and N atoms plays a crucial role in facilitating structural stability. Furthermore, we identified a novel phase for LaN , which has a lower enthalpy compared to the previously reported phase. N atoms in LaN are polymerized into infinite N chains. Calculations demonstrate the potential recoverability of LaN and LaN under atmospheric conditions while preserving their initial polynitrogen configuration. From the perspective of detonation pressure and detonation velocity, LaN and LaN exhibit excellent explosive performance in comparison to TNT and HMX, with estimated energy densities of 0.9 and 1.54 kJ g , respectively, indicating their potential utility as high-energy-density materials.