Defect and phase stability of solid solutions of Mg2X with an antifluorite structure: An ab initio study

► First-principles study of the stability of Mg2Si-Mg2X alloys (X=Ge or Sn) and their defects. ► Mg2Si-Mg2Ge alloys form a complete series of solid solutions. ► Miscibility gap is found in Mg2Si-Mg2Sn alloys. ► Interstitial defects are more stable in Mg2Si and induce n-doping.