Tracer impurity diffusion in amorphous Ni_xZr_1-x alloys

Impurity tracer diffusion coefficients for Co and Hf were measured in a series of amorphous Ni_xZr_1-x alloys at various temperatures for 0.3<x<0.7. The diffusion coefficients for Co, an impurity with small atomic radius were, depending on alloy composition and temperature, two to four orders of magnitude larger than those for Hf, an impurity with large atomic radius. Whereas the Hf tracer diffusion coefficients are independent of alloy composition, those of Co decrease strongly with increasing Ni concentration. These results suggest that the diffusion mechanisms for atoms with small or large atomic radii are different in amorphous Ni-Zr alloys.