Amorphous Ni-Zr alloys as barriers for self-diffusion

The diffusivity of Ni at 250 °C through an amorphous ${\mathrm{Ni}}_{50}$ ${\mathrm{Zr}}_{50}$ alloy sandwiched between pure Ni and pure Zr is at least a factor of ${10}^4$ below that for Ni in crystalline Zr. This result contradicts a recently proposed diffusion model for amorphous phase formation by solid-state reactions, because the amorphous layer acts as a diffusion barrier to self-diffusion.