The role of Fe in the hexagonal close-packed Zr diffusion process was analyzed with regard to its ultra-fast diffusion (up to 9 orders of magnitude higher than self-diffusion at 779 to 1128K) and the enhancement observed in the self and substitutional diffusion produced by its presence as an impurity. Ab initio calculations, using computer codes, were performed in order to determine the actual Fe minimum energy configuration within the hexagonal close-packed Zr matrix and its interaction with vacancies. Several off-centre quasi-interstitial positions, with energies similar to substitutional Fe, were found. A comparison with diffusion coefficient measurements and Mössbauer experiments permitted neglect of the substitutional position of the Fe atom, as well as confirming that its presence created a considerable lattice distortion; together with an increment in the number of vacancies. The above effects could be responsible for enhancement of the self and substitutional diffusion, whereas the large number of quasi-interstitial positions for Fe could be at least partially responsible for ultra-fast Fe diffusion.

Ab initio Approach to the Effect of Fe on the Diffusion in HCP Zr. R.A.Pérez, M.Weissmann: Journal of Nuclear Materials, 2008, 374[1-2], 95-100