Radioactive 57 Mn isotopes have been implanted into Si 1− x Ge x crystals (x≤ 0.1) at elevated temperatures for Mössbauer studies of the diffusion of interstitial 57 Fe daughter atoms. The atomic jump frequency is found to increase upon Ge alloying. This is attributed to a lowering of the activation energy, ie the saddle point energy at hexagonal interstitial sites with Ge neighbour atoms.