Investigation on Mg₃Sb₂/Mg₂Si Heterogeneous Nucleation Interface Using Density Functional Theory

In this study, the cohesive energy, interfacial energy, electronic structure, and bonding of Mg₂Si (111)/Mg₃Sb₂ (0001) were investigated by using the first-principles method based on density functional theory. Meanwhile, the mechanism of the Mg₃Sb₂ heterogeneous nucleation potency on Mg₂Si grains was revealed. The results indicated that the Mg₃Sb₂ (0001) slab and the Mg₂Si (111) slab achieved bulk-like characteristics when the atomic layers N ≥ 11, and the work of adhesion of the hollow-site (HCP) stacking structure (the interfacial Sb atom located on top of the Si atom in the second layer of Mg₂Si) was larger than that of the other stacking structures. For the four HCP stacking structures, the Sb-terminated Mg₃Sb₂/Si-terminated Mg₂Si interface with a hollow site showed the largest work of adhesion and the smallest interfacial energy, which implied the strongest stability among 12 different interface models. In addition, the difference in the charge density and the partial density of states indicated that the electronic structure of the Si-HCP-Sb interface presented a strong covalent, and the bonding of the Si-HCP-Mg interface and the Mg-HCP-Sb interface was a mixture of a covalent bond and a metallic bond, while the Mg-HCP-Mg interfacial bonding corresponded to metallicity. As a result, the Mg₂Si was conducive to form a nucleus on the Sb-terminated-hollow-site Mg₃Sb₂ (0001) surface, and the Mg₃Sb₂ particles promoted the Mg₂Si heterogeneous nucleation, which was consistent with the experimental expectations.