Crystal structures and properties of nitrogen oxides under high pressure

Abstract

First-principles calculations were performed to investigate the structural, electronic, and elastic properties of N₂O₄ and N₂O₅. Two new phases, namely, P4₂2₁2 N₂O₄ and P2₁/m N₂O₅, are determined under high pressure through an ab initio evolutionary algorithm. For N₂O₄, the Im3 phase transforms to the P4₂2₁2 structure at 35 GPa. The pressure–volume curves of N₂O₄ and N₂O₅ show that this transition has a first-order nature. The calculated phonon dispersion and elastic constants of Im3 N₂O₄, P4₂2₁2 N₂O₄, and P2₁/m N₂O₅ demonstrate that the dynamic and mechanical stable pressure ranges are 2–35, 35–80, and 29–120 GPa, respectively. The electronic properties and projected density of states imply that these three structures are insulators. Furthermore, the N–N and N–O bond length of nitrogen oxides under high pressure are discussed.