High-pressure phase stability, electronic Structure and superconductivity in Barium-Tin intermetallics: a first-principles study

Abstract This study employs crystal structure prediction and first-principles calculations to systematically investigate the high-pressure phase diagram and superconducting properties of barium-tin (Ba-Sn) intermetallic compounds at 100 and 200 GPa. We identify several thermodynamically stable phases, including Ba 2 Sn, BaSn 2 , BaSn 3 at 100 GPa, with additional novel stable phases Ba 4 Sn and BaSn 6 emerging at 200 GPa. All phases exhibit metallic behavior and dynamic stability. Structural motifs range from covalent Sn-Sn networks in Sn-rich compounds ( e.g. , graphene-like layers in P 6 /mmm BaSn 2 ) to ionic/metallic bonding in Ba-rich phases ( e.g. , I 4 /m Ba 4 Sn). Electron localization function (ELF) analyses reveal strong covalent Sn-Sn bonding in Sn-rich systems, while Ba-rich phases show localized atomic ELF maxima. Superconducting transition temperatures ( T c ) remain low across the system, with Ba 4 Sn exhibiting the highest T c (0.33 K) at 200 GPa. The superconducting mechanism in Ba-rich phases is attributed to electron-phonon coupling involving Ba d -orbitals, contrasting with the previous reported lone-pair-driven coupling in Sn-rich BaSn 5 . The study highlights pressure-induced structural transitions, bonding evolution, and the contrasting superconducting mechanisms in Sn-rich versus Ba-rich phases.