Effect of Different Concentrations of Co Doping on the Properties of η′-Cu6Sn5 and Ni3Sn4: First-Principles Study

In the field of electronic packaging, Ni3Sn4-based and eta '-Cu6Sn5-based compounds are common Sn-based intermetallic compounds into which doping of other appropriate elements has been widely studied. Herein, the structural stability, mechanical properties, and electronic structures of (Ni,Co)(3)Sn-4 and eta '-(Cu,Co)(6)Sn-5 are systematically investigated using first-principles calculations. By comparing the heat of formation of the doped and undoped intermetallic compounds, it is found that the doped Ni3Sn4 structure has a higher heat of formation and a less stable structure, while the doped eta '-Cu6Sn5 structure has a lower heat of formation and a more stable structure. The doped Ni3Sn4 exhibits an increasing bulk modulus (B) and Young's modulus (E), and the doped eta '-Cu6Sn5 exhibits a gradually increasing bulk modulus (B). These findings suggest that doping improves the rigidity and elastic deformation properties of the two intermetallic compounds. And yet the anisotropy of both intermetallic compounds is decreasing as doping concentration increases. According to the calculations of the electronic structures, the doped (Ni,Co)(3)Sn-4 structure and the doped eta '-(Cu,Co)(6)Sn-5 structure exhibit stronger metallicity. In addition, stronger Co-Sn ionic bonds are formed in the doped Ni3Sn4 and eta '-Cu6Sn5 structures. This suggests that the doped Ni3Sn4 and eta '-Cu6Sn5 structures are harder.