Diffusion mechanisms in under-cooled binary metal liquids of Zr67Cu33

We present results of computer simulations of molten Zr67Cu33 at temperatures down to the glass transition. Analyzing the atomic displacements we observe two processes: a hopping of atoms by nearest neighbor distances and a more flow-like motion which is astonishingly similar for Cu-and Zr-atoms. With decreasing temperature the jumps become increasingly reversible and their contribution to long range diffusion diminishes. The data are analyzed in the frame of a simple model. Whereas the jump-rates obey an Arrhenius law the rapid drop of diffusion results from the increased reversibility. (C) 1998 Elsevier Science Ltd. All rights reserved.