By means of an electron microprobe the diffusion of silicon in iron–silicon was measured in the temperature range from 900 to 1100°C, using diffusion couples containing 7.64 and 11.1 at% Si. The diffusion coefficients turned out to be concentration dependent. Activation energies and frequency factors deduced are given.

Results of measurements between 533 and 1093 °C of the diffusion coefficient of Fe59 in two single crystals of FeSi (7.64 and 11.1 at% Si, respectively) are presented. For the lower temperatures a newly developed chemical sectioning technique was employed. The results show a marked ferromagnetic effect, i.e. the activation energy is strongly peaked at the Curie temperature. The results are analysed in terms of the Zener‐LeClaire theory in combination with an argument that relates the enthalpy of vacancy formation with the change in magnetic specific heat of the matrix upon introduction of a vacancy. The latter argument can also be used exclusively when related to the introduction of an activated complex in the matrix.

The correlation factor for impurity diffusion by single vacancies in the diamond structure is calculated taking into account eight distinct vacancy-atom exchange rates. Arguments are given that such a model is physically more realistic than the usual four frequency model. It turns out that the difference from the results obtained by the latter model can become large. A long range Coulombic impurity-vacancy interaction is also included.

An expression for the correlation factor of impurity diffusion in the diamond structure as a function of five distinct atom-vacancy exchange rates is derived.Furthermore, the effect on the correlation factor of electrostatic vacancy-impurity interaction is included in the calculation. Differences with results obtained by other authors are discussed.