First principles investigation of the vacancy-mediated impurity diffusion in dilute Zr-X (X = Sc, Y, Ce) alloys

Abstract

The vacancy-mediated diffusion in dilute Zr-X (X = Sc, Y, Ce) alloys were investigated by adopting the eight-frequency model based on density functional theory calculations within the general gradient approximation. The correlation between the diffusion related properties and the intrinsic properties of the solute was revealed in terms of size and chemical effects. It is found that Sc is beneficial to restrain the diffusion in the Zr alloy, and the parameters governing diffusion in these alloys correlate well with the atomic radius difference (ΔR) and the absolute electronegativity difference (|ΔEl|) between X and Zr. With the increasing of ΔR and |ΔEl| from Sc to Ce, the equilibrium vacancy concentration increases while the X-vacancy migration energy decreases, originating from the local lattice distortion near X and the chemical interaction between Zr and X. As a result, the diffusion coefficients (D) show an order of DZr-Sc < DZr-Y < DZr-Ce. Moreover, the diffusion within the basal plane is larger than that between the adjacent basal planes except for Ce, and the difference between them becomes smaller from Sc to Ce, resulting from the anisotropy of the HCP-Zr structure as well as the combination of size and chemical effects.