Ni self-diffusion in glass forming Pd-Ni-S melts.

The Ni self-diffusion in glass forming Pd40Ni40S20, Pd37Ni37S26and Pd31Ni42S27melts was probed by incoherent, quasielastic neutron scattering over a temperature range between 773 and 1023 K. The Ni self-diffusion coefficients are on a 10-10 m2 s-1-10-9 m2 s-1scale and barely change with composition. Each composition exhibits an Arrhenius-type temperature dependence of the Ni self-diffusion coefficients, which results in activation energies ranging fromEA= 348 ± 16 meV for Pd40Ni40S20toEA= 387 ± 6 meV for Pd37Ni37S26. The structural relaxation shows a stretched exponential behavior even far above the liquidus temperatures. In addition, the viscosity of the Pd37Ni37S26melt was measured under reduced gravity conditions. The diffusion calculated from the viscosity reveals a significant deviation from the measured Ni self-diffusion by a factor between 4 and 8. This may indicate a dynamic decoupling between the atoms within the Pd-Ni-S equilibrium melts.