Phonons - A diffusion motor in intermetallics?

We search for the reason for the extraordinarily high diffusivity of Fe and Ni in the DO₃ intermetallics Fe₃Si and Ni₃Sb. Recent quasielastic neutron scattering and Mössbauer spectroscopy studies revealed the elementary diffusion jump mechanism: in stoichiometric Fe₃Si and in Ni₃Sb diffusion takes place via nearest-neighbour jumps in the Fe/Ni sublattice. Considering this simple mechanism, the high diffusivities remain puzzling. Measurements of the phonon dispersion have been performed in order to check if diffusion in these intermetallics is phonon-assisted as in the high-temperature phases of the Ti-group metals. The migration barriers of low energy derived from the phonon data allow to draw clear conclusions on the reason for fast diffusion in these alloys.