The diffusivity of Fe and Ge in this DO3 phase was studied, as a function of temperature and composition, by using a tracer sectioning technique and 59Fe and 71Ge radioisotopes (tables 7 and 8). It was observed that Fe diffusion in this structure was much faster, and that the corresponding activation enthalpy was appreciably lower than in body-centered cubic Fe or in disordered Fe-rich Fe-Si alloys. It was most rapid in the nearly stoichiometric compound. On the other hand, the diffusion of Ge and Si was considerably slower and the activation enthalpy was higher than in the disordered phases. It was noted that, whereas Fe diffusion was strongly dependent upon the alloy composition, the diffusion of Ge was less affected by the Si concentration. The main conclusion was that the diffusion of Fe atoms occurred via nearest-neighbor jumps on the Fe sub-lattice, and was mediated by thermal vacancies which were present in high concentrations. Diffusion in Fe-rich alloys was affected by magnetic order/disorder transitions. In one experiment, using 31Si tracer, it was found that Si and Ge diffused at very similar rates. It was concluded that diffusion of the 2 components of the DO3 ordered material was decoupled and that self-diffusion of the components obeyed the so-called Cu3Au rule.

A.Gude, H.Mehrer: Philosophical Magazine A, 1997, 76[1], 1-29

Table 7

Diffusivity of 59Fe in Fe-Si Alloys

Table 8

Diffusivity of 71Ge in Fe-Si Alloys