First-Principles Study of Atomic Diffusion by Vacancy Defect of the L1₂-Al₃M (M = Sc, Zr, Er, Y) Phase

Atomic diffusion by the vacancy defect of L1₂-Al₃M (M = Sc, Zr, Er, Y) was investigated based on a first-principles calculation. The point defect formation energies were firstly evaluated. Then, the migration energy for different diffusion paths was obtained by the climbing-image nudged elastic band (CI-NEB) method. The results showed that Al atomic and M atomic diffusions through nearest-neighbor jump (NNJ) mediated by Al vacancy (V_Al) were, respectively, the preferred diffusion paths in Al₃M phases under both Al-rich and M-rich conditions. The other mechanisms, such as six-jump cycle (6JC) and next-nearest-neighbor jump (NNNJ), were energetically inhibited. The order of activation barriers for NNJ(Al-V_Al) was Al₃Zr < Al₃Y < Al₃Er < Al₃Sc. The Al₃Sc phase had high stability with a high self-diffusion activation barrier, while the Al₃Zr and Al₃Y phases were relatively unstable with a low self-diffusion activation energy. Moreover, the atomic-diffusion behavior between the core and shell layers of L1₂-Al₃M was also further investigated. Zr atoms were prone to diffusion into the Al₃Y core layer, resulting in no stable core-shelled Al₃(Y,Zr), which well agreed with experimental observation.