Dependence of tracer diffusion on atomic size in amorphous Ni-Zr

Tracer diffusion coefficients for several impurities and Ni self-atoms were measured in amorphous (a-) ${\mathrm{Ni}}_{50}$ ${\mathrm{Zr}}_{50}$ at 573 K using secondary-ion-mass spectroscopy, Rutherford backscattering, and radioactive tracer methods. The results showed that atomic mobility in the a-Ni-Zr alloy depends strongly on atomic size, decreasing rapidly with increasing atomic radius. This diffusion behavior is similar to that in α-Zr and α-Ti and is suggestive of an interstitial-like mechanism of diffusion. The consequences of these results for solid-state amorphization transformations are discussed.