Novel high-pressure phases of nitrogen-rich Y-N compounds

Five new high-pressure phases (I4̄3d-Y₄N₃, R3c-Y₂N₃, P1̄-II-YN₄, P1̄-YN₆, and P31c-YN₈) are proposed by the crystal structure prediction. A series of polynitrogen forms were achieved in the nitrogen-rich Y-N compounds, including diatomic N₂, an isolated N₈ chain, an infinite N chain with an N₆ unit, and an infinite N layer with bent N₁₈ rings. The high energy densities of P1̄-II-YN₄ (1.98 kJ g^-1), P1̄-YN₆ (2.35 kJ g^-1), and P31c-YN₈ (3.77 kJ g^-1) make them potential high energy density materials. More importantly, P1̄-II-YN₄, P1̄-YN₆, and P31c-YN₈ exhibit excellent explosive performance, with detonation pressures 4-8 times that of TNT (19 GPa) and detonation velocities 1-2 times that of TNT (6.90 km s^-1). The electronic structure and bonding properties show that the high stability of Y-N compounds originates from the strong N-N covalent bond and the weak Y-N ionic bond interaction. The increase in the transferred charge quantity as the pressure decreased is more conducive to stabilizing the polymeric nitrogen structure, which leads to the metastable properties of P1̄-II-YN₄ and P1̄-YN₆ under ambient conditions. Finally, the infrared (IR) spectra of P1̄-II-YN₄, P1̄-YN₆, and P31c-YN₈ are calculated to provide a reference in experimental synthesis.