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

Five new high-pressure phases (4̄3-YN, 3-YN, 1̄-II-YN, 1̄-YN, and 31-YN) are proposed by the crystal structure prediction. A series of polynitrogen forms were achieved in the nitrogen-rich Y-N compounds, including diatomic N, an isolated N chain, an infinite N chain with an N unit, and an infinite N layer with bent N rings. The high energy densities of 1̄-II-YN (1.98 kJ g), 1̄-YN (2.35 kJ g), and 31-YN (3.77 kJ g) make them potential high energy density materials. More importantly, 1̄-II-YN, 1̄-YN, and 31-YN 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). 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 1̄-II-YN and 1̄-YN under ambient conditions. Finally, the infrared (IR) spectra of 1̄-II-YN, 1̄-YN, and 31-YN are calculated to provide a reference in experimental synthesis.