Isotope effect of diffusion in the supercooled liquid state of bulk metallic glasses

The isotope effect, E = (D-alpha/D-beta - 1)/(root m(beta)/m(alpha) - 1), o f cobalt diffusion in the deeply supercooled liquid state of the bulk metal lic glass formers Zr46.7Ti8.3Cu7.5Ni10Be27.5 and Zr65Cu17.5Ni10Al7.5 has be en measured employing the radio-tracers Co-57 and Co-60 in conjunction with serial sectioning by means of ion-beam depth profiling. In both alloys a s mall mass dependence with E approximate to 0.10 is observed. This dependenc e has no temperature dependence in a range of 120 K in the supercooled liqu id state encompassing four orders of magnitude in the diffusivity. We sugge st that these results show that long-range diffusion in a deeply supercoole d liquid is not mediated by viscous flow but proceeds by collective hopping processes involving about 10 atoms. (C) 1999 Elsevier Science B.V. All rig hts reserved.