Abstract
The potential structures of magnesium nitride with a chemical composition of Mg3N2 are examined by utilizing a widely adopted evolutionary methodology for crystal structure prediction. In addition to the previously proposed phases (α-, β- and γ-Mg3N2), we find five high-pressure phases for Mg3N2: (1) a Cmc21 symmetric structure (e-Mg3N2) at 27 GPa, (2) a R3c symmetric structure (τ-Mg3N2) at 30 GPa, (3) a Cmcm symmetric structure (ω-Mg3N2) at 53 GPa, (4) a Ima2 symmetric structure (λ-Mg3N2) at 68 GPa, and (5) a Ibam symmetric structure (μ-Mg3N2) at 115 GPa. All these phases are mechanically and dynamically stable by checking the elastic constants and phonon dispersion. All phases are direct band gap semiconductors except that the ω-Mg3N2 phase has a nontrivial indirect band gap. Mechanical properties calculations reveal that the γ-Mg3N2 phase has superior ductility than other phases. The Vickers hardness of each phase has been evaluated to be about 15 GPa based on an empirical relation.
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