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

Abstract

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 fromE_A= 348 ± 16 meV for Pd₄₀Ni₄₀S₂₀toE_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 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.

Keywords: bulk metallic glasses; metallic melts; quasielastic neutron scattering; self-diffusion; sulfur; viscosity.