Capturing High-Energy Polymeric Nitrogen Structures Stabilized by Lutetium at Ambient Conditions

Polynitrogen with high energy and environmental friendliness has exhibited potential application in military and civilian fields. In this study, first-principle calculations were employed to conduct a comprehensive investigation of the nitrogen-rich Lu-N compounds. The research yielded ten novel polynitrides: P2₁/c-LuN₂, P1̅-LuN₃, P1̅-LuN₄, P2₁/m-LuN₄, P1̅-LuN₅, P1̅-LuN₆, P1̅-LuN₈, Cm-LuN₉, I4/m-LuN₁₀, and Cmcm-LuN₁₀. It is noteworthy that two novel polymeric nitrogen structures have been observed in our prediction: an infinite tripodic-N₄ chain formed in P2₁/m-LuN₄, and a heart-shaped N₁₂ ring band formed in Cm-LuN₉. Excellent stabilities were observed in the calculated Lu-N compounds; P2₁/m-LuN₄ and P1̅-LuN₈ are quenchable under ambient conditions. Meanwhile, the polynitrogen structures of P1̅-LuN₆ and Cm-LuN₉ are calculated to decompose into thermally stable N₆ rings and infinite N-chains under ambient conditions, respectively. Cmcm-LuN₁₀ is thermodynamically stable due to its high symmetry and efficient packing of the chain-like N₁₀ cage. Moreover, the Lu-N compounds, which display favorable energy density (mass energy density (E_d) = 1.60-3.59 kJ/g; volumetric energy density (E_V) = 11.32-15.65 kJ/cm³), are prospective candidates for environmentally friendly high-energy density materials. These results provide a good theoretical guide for the experimental synthesis of new energetic materials.