Diffusion of tellurium at nickel grain boundaries: a first-principles study
The knowledge of the behavior of Te in nickel grain boundaries (GB) is of significant importance for the application of nickel alloys in molten salt reactors. The atomic structures, stabilities, segregation behaviors and diffusion barriers of Te are studied for the bulk, surfaces and four kinds of GBs of nickel. Our first-principles calculations indicate the segregation of Te is most favorable at Σ = 5 (021) GB and the weakest at Σ = 3 (111) GB. The diffusion barriers of Te increase in sequence: Σ = 11 (11), Σ = 9 (221), Σ = 3 (111) and Σ = 5 (021). The calculated diffusion barrier of Te on Σ = 11 (11) is 0.35 eV lower than in the bulk, indicating a fast diffusion of Te along this GB. We also consider the effect of strain on the diffusion and find it to be sensitive to the different GB types. When the tensile strain is up to 4%, the diffusion barriers of Te are lowered by 0.51 eV and 0.15 eV for Σ = 5 (021) and Σ = 11 (11), respectively. In contrast, this effect for Σ = 3 (111) is negligible.