High nitrogen polymer in silver polynitrides

The Ag–N system is enriched by proposing four polymeric structures in first-principles calculations at high-pressure. The proposed P-1-AgN₂ and P2₁/c-AgN₂ not only break the new record in the polymeric configuration of MN₂ compound, but also in the energy density. In the MN₂ stoichiometric ratio, the infinite armchair-antiarmchair chain and the layered polymer structure are reported for the first time in P-1-AgN₂ and P2₁/c-AgN₂, indicating that the highly polymerized structure can also be formed in nitrides with low nitrogen content at high pressure. The mechanism of structure evolution behaviors of AgN₂ under pressure is revealed by the analysis of atomic orbital hybridization. Meanwhile, the high energy densities are obtained in P-1-AgN₂ (1.76 kJ g⁻¹) and P2₁/c-AgN₂ (2.01 kJ g⁻¹) compared to all the reported MN₂ nitrides. In addition, the infinite band-shaped structure and infinite curve layer structure are obtained in P-1-AgN₅ and C2/m-AgN₆, respectively. The energy densities of P-1-AgN₅ (3.82 kJ g⁻¹) and C2/m-AgN₆ (4.51 kJ g⁻¹) are comparable to or larger than that of TNT (4.3 kJ g⁻¹). Moreover, P-1-AgN₂, P2₁/c-AgN₂, P-1-AgN₅, and C2/m-AgN₆ exhibit excellent explosive performance in terms of detonation velocity and detonation pressure.