First-Principles Study of Thermodynamical and Elastic Properties of η′-(Cu,Co)₆Sn₅ Ternary Alloys

First-principles calculations were made to investigate the formation energy and elastic properties of η′-Cu₆Sn₅-based intermetallic compounds (IMCs) with different amounts of Co substitutional atom concentrations. The possible Co substitutional sites in η′-Cu₆Sn₅ structures are examined. The formation energy of substitutional Co in η′-Cu₆Sn₅ is reduced with increasing Co concentration. The effect of Co on the elastic modulus and ductility of η′-Cu₆Sn₅ dramatically increased the elastic properties of Cu-Sn IMCs in the range 0–27.27 at.%. Cu₄Co₂Sn₅ has the highest Young’s modulus, bulk modulus and shear modulus with a maximum Poisson’s ratio of 0.32 with 18.18 at.% Co concentration. Ductility for these compounds is further analyzed by calculating the ratio of B/G and Cauchy’s stress (C₁₂ − C₄₄) and the results indicate that η′-Cu₆Sn₅ with Co substitutions should have a better ductility than the pure η′-Cu₆Sn₅ structure. The electronic structures of Co-substituted η′-Cu₆Sn₅ are analyzed and the increasing hybridization between Co-d and Sn-p accounts for the improved phase stability and elastic modulus of η′-Cu₆Sn₅ with Co addition up to 18.18 at.%.