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

Abstract

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.