Radiotracer diffusion measurements were performed on bulk metallic glass-forming Pd–Cu–Ni–P alloys. Serial sectioning was performed by grinding and ion-beam sputtering. In the glassy state, as well as in the deeply supercooled state below the critical temperature Tc, where the mode coupling theory predicted a freezing-in of liquid-like motion, the very small experimentally determined isotope effects indicated a highly collective hopping mechanism which involved some 10 atoms. Below Tc, the temperature dependence exhibited Arrhenius-type behaviour, with an effective activation enthalpy of 3.2eV. Above Tc, the onset of liquid-like motion was revealed by a gradual decrease in the effective activation energy and by the validity of the Stokes–Einstein equation, which was found to break down below Tc. This strongly supported the mode-coupling scenario. The Stokes–Einstein equation was tested for other constituents of the alloy. The Co isotope effect measurements, which had never been carried out near to Tc in any material, showed atomic transport up to the equilibrium melt to be far away from the hydrodynamic regime of uncorrelated binary collisions.

Diffusion in Bulk-Metallic Glass-Forming Pd-Cu-Ni-P Alloys - from the Glass to the Equilibrium Melt. K.Rätzke, V.Zöllmer, A.Bartsch, A.Meyer, F.Faupel: Journal of Non-Crystalline Solids, 2007, 353[32-40], 3285-9