Impact of Nitrogen Polymerization on the Properties of MgN2 Polymorphs: Ultrasoft Semiconductor versus Hard Wide-Bandgap Semiconductor

Abstract

Utilizing evolutionary algorithms and density functional theory calculations, we predict two novel semiconducting phases of MgN₂ (C2/m-MgN₂ and R3̅-MgN₂) that are dynamically stable at ambient pressure and thermally stable at 300 and 600 K. Interestingly, the different polymerization forms of nitrogen in the C2/m and R3̅ phases lead to significantly different mechanical properties. Specifically, C2/m-MgN₂ is an exceptionally rare ultrasoft semiconductor (H_v = 0.11 GPa, lower than aluminum and silver) with high anisotropy (A^U = 24.85), while R3̅-MgN₂ is a hard semiconductor (H_v = 17.72 GPa) with a low melting point (T_m = 1057 ± 13 K, nearly half that of P6₃mc-AlN and P31c-Si₃N₄). Further analysis of explosive performance revealed that R3̅-MgN₂ has a higher energy density than Cmmm-MgN₄, despite the latter having a higher nitrogen content, due to the unique wrinkled six-membered N₆ rings in R3̅-MgN₂. These findings provide valuable insights into the impact of nitrogen polymerization on the mechanical and explosive performances of nitrogen-rich metal nitrides and offer guidance for designing nitrides with tailored properties.