Low pressure metastable single-bonded solid nitrogen phases

Abstract

Within the framework of the density functional theory, the possibility of the formation of single-bonded solid atomic nitrogen phases as a result of adiabatic compression of molecular and cluster nitrogen structures at zero temperature has been studied. It has been demonstrated that nitrogen clusters N₈(C_2v)–B, which are theoretically predicted as one of the promising candidates for high energy density materials, can transform under compression into a solid atomic phase with crystal lattice symmetry P2₁. The P2₁ phase is dynamically stable under decompression to zero pressure. It is shown that the ε-N₂ molecular phase transforms under compression into a solid atomic phase with Rc symmetry, and retains a vibrationally stable crystal structure when the pressure is reduced to 30 GPa, transforming into a stable cluster form at lower pressures. The atoms in the P2₁ and Rc solid atomic phases are linked by single bonds; therefore, these structures can store a large amount of energy ≈1.4 eV per atom. A detailed comparison of the properties of new P2₁ and Rc solid atomic phases with other nitrogen crystal structures that are dynamically stable at low pressures has been carried out.