The self-diffusion of Fe and the impurity diffusion of Ge in this B20 phase were studied as a function of temperature by using the radio-tracer method and the isotopes, 59Fe and 71Ge. The latter was used to simulate Si self-diffusion. Both of the diffusivities were very small, and the values for Fe were some 1 to 2 orders of magnitude smaller than those for Ge. This uncoupled diffusion was explained in terms of vacancy-based diffusion on the Fe and Si sub-lattices. Both of the diffusivities attained a value of about 10-14m2/s at 1683K. The overall results (tables 5 and 6, figure 11) for volume diffusion could be described by:

59Fe      D (m2/s) = 3.44 x 10-3 exp[-3.88(eV/atom)/kT]

71Ge      D (m2/s) = 3.27 x 10-8 exp[-2.09(eV/atom)/kT]

The triple products for grain-boundary diffusion were calculated from the slope of the grain boundary-dominated sections of penetration profiles. The results (tables 7 and 8, figure 12) for boundary diffusion could be described by:

59Fe      D (m3/s) = 4.30 x 104 exp[-4.47(eV/atom)/kT]

71Ge      D (m3/s) = 3.34 x 10-2 exp[-2.42(eV/atom)/kT]

Diffusion in the B20-Type Phase FeSi. M.Salamon, H.Mehrer: Philosophical Magazine A, 1999, 79[9], 2137-55

Table 5

Bulk Diffusivity of 59Fe in FeSi

Table 6

Bulk Diffusivity of 71Ge in FeSi

Figure 11

Bulk Diffusivity of 59Fe and 71Ge in FeSi

Table 7

Grain-Boundary Diffusivity of 59Fe in FeSi

Table 8

Grain-Boundary Diffusivity of 71Ge in FeSi

Figure 12

Grain Boundary Diffusivity of 59Fe and 71Ge in FeSi