Diffusion in liquid metals between the glass transition and the evaporation temperature

Based on the results of recent impurity diffusion measurements of Al and Co in bulk amorphous alloys (''vitreloyl''= Zr41Ti14Cu12.5Ni10Be22.5 and ''vitreloy4''= Zr46.7Ti8.3Cu7.5Ni10Be27.5) in the supercooled temperature region around the glass transition and on earlier results of self- and impurity diffusion, the general temperature dependence of diffusion in the disordered (liquid and highly undercooled liquid) state of (amorphous) metals is discussed, which is expected to change from a type of T-square law at temperatures well above the melting point to an Arrhenius-like dependence at low temperatures between the glass point and the crystallization temperature (supercooled liquid). The change in the temperature dependence must take place in a temperature region below the melting point around a ''transition temperature'' T-C. In this region diffusion data are not yet available but from possible extrapolations into this region it seems that the region is fairly narrow. The estimations support the view that the transition region coincides with the break-down of transversal lattice vibrations (shear waves) at atomic vibration frequencies.