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

Abstract

Novel Sr-N phases under varying moderate pressures are explored, utilising first-principles calculations to investigate their thermodynamic, structural, and electronic characteristics. Through thorough analyses, including convex hull-based thermodynamic stability assessments, phonon calculations for dynamical stability confirmation, and mechanical property evaluations, we identify four stable structures—SrN, SrN2, SrN3, and SrN4. Electronic band structure calculations reveal non-zero band gaps for SrN and SrN2 (i.e., 0.30 and 0.22 eV respectively), contrasting with the metallic behaviour observed in SrN3 and SrN4. Additionally, the study unveils the superconducting behaviour of SrN4 within the pressure range of 10-50 GPa, with a peak superconducting critical temperature (Tc) reaching 13.7 K at 10 GPa, reflecting the enhancement of Tc under pressures attributed to the introduction of N. These findings provide valuable insights into the diverse properties of Sr-N phases under varying pressure conditions, opening avenues for further exploration and potential applications in metal nitrides under pressures.

Keywords: Sr-N phases, Pressure, metal nitride compounds, Convex hull, superconductivity, Spectral function