Alkaline-earth metal (Mg) polynitrides at high pressure as possible high-energy materials

Abstract

The P1̄-MgN ₃ and P1̄-MgN ₄ are predicted to become energetically stable under pressure, suggesting that it may be prepared by high-pressure synthesis. P1̄-MgN ₃ and P1̄-MgN ₄ are expected to release an enormously large amount of energy (2.83 and 2.01 kJ g ⁻¹). The present study encourages experimental exploration of these promising materials in the future.

Abstract

The high-pressure structural evolutionary behaviors of magnesium polynitrides were studied up to 100 GPa using first-principles calculations. Using the unbiased structure searching method, five stable chemical stoichiometries of magnesium polynitrides (MgN, Mg ₂N ₃, MgN ₂, MgN ₃, and MgN ₄) were theoretically predicted at high pressures. The predicted MgN _x compounds contain a rich variety of polynitrogen forms ranging from charged molecules (one-dimensional bent molecules N ₃, planar triangle N ₄ to benzene-like rings N ₆) to extended polymeric chains (N _∞). To the best of our knowledge, this is the first time that stable bent molecules N ₃, planar triangle N ₄, and polymeric chains (N _∞) were predicted in alkaline-earth metal polynitrides. The decomposition of P1̄-MgN ₃ and P1̄-MgN ₄ are expected to be highly exothermic, releasing an energy of approximately 2.83 kJ g ⁻¹ and 2.01 kJ g ⁻¹, respectively. Furthermore, P1̄-MgN ₄ can be synthesized at several GPa. The results of the present study suggest that it is possible to obtain energetic polynitrogen in main-group nitrides under high pressure.