Activation Volume for Hf Diffusion in an Amorphous Ni0.54Zr0.46Alloy

In this Letter we present the results of a diffusion study of Hf in a N${\mathrm{i}}_{0.54}$Z${\mathrm{r}}_{0.46}$ amorphous alloy. We have measured the diffusion properties with and without pressure, up to 1 GPa. From these measurements we can deduce an Arrhenius behavior of the diffusion, with an activation energy of 0.76 eV and a pre-exponential factor of $7.4\times {10}^{-17\mathrm{}}{\mathrm{m}}^2/\mathrm{s}$. The activation volume amounts to 8.5 ${\mathrm{Å}}^3$. Activation volume and energy are related by the Keyes relationship. We then discuss to what extent presently proposed diffusion mechanisms, point defects, or collective processes can be tested against these results.