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.