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 proposedP-1-AgN₂andP2₁/c-AgN₂not only break the new record in the polymeric configuration of MN₂compound, but also in the energy density. In the MN₂stoichiometric ratio, the infinite armchair-antiarmchair chain and the layered polymer structure are reported for the first time inP-1-AgN₂andP2₁/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 AgN₂under pressure is revealed by the analysis of atomic orbital hybridization. Meanwhile, the high energy densities are obtained inP-1-AgN₂(1.76 kJ g^-1) andP2₁/c-AgN₂(2.01 kJ g^-1) compared to all the reported MN₂nitrides. In addition, the infinite band-shaped structure and infinite curve layer structure are obtained inP-1-AgN₅andC2/m-AgN₆, respectively. The energy densities ofP-1-AgN₅(3.82 kJ g^-1) andC2/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, andC2/m-AgN₆exhibit excellent explosive performance in terms of detonation velocity and detonation pressure.