FIRST-PRINCIPLES STUDY OF ELECTRONIC STRUCTURAL, ELASTIC, AND THERMODYNAMIC PROPERTIES OF Sn-Bi ALLOYS

Structural, electronic, elastic and thermodynamic properties of the SnxBi(16-x) (x=7, 9, 10, 12, 13, 14, 15) solid solution alloys with tetragonal structure were investigated by means of first-principles calculations within the framework of density functional theory. The results of enthalpies of formation and cohesive energy show that the stability of the alloys increases with the decrease of the content Bi. The electronic structure was further investigated to understand the underlying mechanism of the structural stability of the SnxBi(16-x) alloys. The single-crystal elastic constants were calculated, showing that the SnxBi(16-x) alloys are mechanically stable structure. Then the bulk modulus B, Young's modulus E, shear modulus G and Poison's ratio v were estimated for polycrystalline SnxBi(16-x) alloys from the elastic constants. The ductility and plasticity of SnxBi(16-x) alloys were improved with decrease of the content of Bi. The elastic anisotropy was also further discussed in details. The substitution of Sn atoms by Bi makes the SnxBi(16-x) alloys elastically more isotropic for the {001} shear plane along the < 010 > direction. Finally, thermodynamic properties such as the Debye temperatures, the specific heat, and melting temperature for the SnxBi(16-x) alloys were estimated from elastic properties.