Pressure-stabilized GdN₆ with an armchair–antiarmchair structure as a high energy density material

The quest for high-energy-density materials is an active research field in materials science and industrial applications. Using the swarm-intelligence structure search method and first-principles calculations, we identify several hitherto unknown gadolinium polynitrides (e.g., GdN2, GdN3, GdN4, and GdN6) under high pressures. Interestingly, P GdN6 with armchair- and antiarmchair-like polynitrogen chains can be obtained via the mixtures of GdN or GdN3 and pure nitrogen above a moderate pressure of 27 GPa. Further investigations reveal that P GdN6 is dynamically stable at ambient pressure and has high thermal stability up to 1000 K, suggesting that GdN6 can be recovered to ambient conditions upon synthesis under compression. Its good stability is mainly due to the covalent N–N and ionic Gd–N bonds. Remarkably, P GdN6 has excellent explosive performance comparable to that of TNT from the standpoint of detonation velocity (11.79 km s−1) and detonation pressure (901 kbar). More importantly, GdN6 is found to have a high energy density (1.62 kJ g−1) and volumetric energy density (8.28 kJ cm−3), which make it become the first high-energy-density material amongst lanthanide nitrides. This work provides in-depth insights into the structures and properties of gadolinium nitrides and opens up opportunities to explore high-energy-density materials in lanthanide nitrides.