Transition from semiconductor to conductor of a Mg₂N electride induced by strain

Electrides are a class of materials in which electrons are not bound to atoms but are similar to anions in crystals. To date, there are more than 300 electrides that have been discovered by first-principles. Alkaline-earth metal nitrides (AE₂N, AE = Be, Mg, Ca, Sr, and Ba) are an important component of electride materials. Ca₂N, Sr₂N, and Ba₂N structures have been identified and synthesized in previous research studies. Furthermore, the structures of Be₂N (R3̄m symmetry) and Mg₂N (R3m symmetry) were recently identified. For Mg₂N, it has zero-dimension (0D) interstitial localized electrons and band structure with semiconductor properties, which is significantly different from the other AE₂N structures (two-dimension electrides and metal properties). Consequently, Mg₂N was systematically studied in this work. We found that the pristine Mg₂N was an indirect band gap semiconductor with a band gap of 0.243 eV. It transitioned to a metal when 2% stretch stress was applied to the c-axis. Moreover, at 5% stretch stress, the structure exhibited 2D interstitial localized electrons with the superconducting transition temperature (T_c) of 0.3 K. These studies thus provide a deeper understanding of the physicochemical properties of Mg₂N as an electride.