Ni Self-Diffusion In Glass Forming Pd-Ni-S Melts

The Ni self-diffusion in glass forming Pd40Ni40S20, Pd37Ni37S26 and Pd31Ni42S27 melts 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) m(2) s(-1)-10(-9) m(2) s(-1) scale 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 from E (A) = 348 +/- 16 meV for Pd40Ni40S20 to E (A) = 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 Pd37Ni37S26 melt 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.