From Stability to Superconductivity: A First-Principles Investigation of Sr–N Phases under Pressures and the N-Enhanced Tc Phenomenon

Recent discoveries in high-pressure chemistry have revealed a greater richness in the interaction between transition metals and nitrogen, particularly with the synthesis of various metal nitrides. In this study, we investigate novel Sr–N phases under varying moderate pressures, employing evolutionary algorithms (EAs) and based on first-principles calculations to explore their thermodynamic, structural, and electronic characteristics. Our comprehensive analysis includes assessments of thermodynamic stability based on convex hulls and confirmation of dynamical stability through phonon calculations. Through these analyses, we identify four stable structures─SrN, SrN2, SrN3, and SrN4─along with their corresponding pressure-induced structures presented in a phase diagram. Electronic band structure calculations offer insights into the electronic behaviors of these phases under different pressures. Notably, in the cases of SrN3 and SrN4, the high PDOS at the Fermi energy suggests the potential for superconductivity (SC) in these phases. Furthermore, our study unveils the superconducting behavior of SrN4 within the pressure range of 10–50 GPa, with a peak Tc reaching 13.7 K at 10 GPa. This observation reflects an enhancement of Tc under pressure, attributed to the introduction of nitrogen. These findings provide valuable insights into the diverse Sr–N phases under pressure obtained from evolutionary algorithms and predict the possibility of SC in certain phases, opening avenues for further exploration in metal nitrides under pressures.