Atomic dynamics of metallic glass melts La 50 Ni 15 Al 35 and Ce 70 Cu 19 Al 11 studied by quasielastic neutron scattering

By employing quasielastic neutron scattering, we studied the atomic-scale relaxation dynamics and transport mechanism of ${\mathrm{La}}_{50}{\mathrm{Ni}}_{15}{\mathrm{Al}}_{35}$ and ${\mathrm{Ce}}_{70}{\mathrm{Cu}}_{19}{\mathrm{Al}}_{11}$ metallic glass melts in the temperature range of $g200\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ above their liquidus temperatures. The results show that both liquids exhibit stretched exponential relaxation and Arrhenius-type temperature dependence of the effective diffusion coefficient. The ${\mathrm{La}}_{50}{\mathrm{Ni}}_{15}{\mathrm{Al}}_{35}$ melt exhibits an activation energy of 0.545 \ifmmode\pm\else\textpm\fi{} 0.008 eV and a stretching exponent \ensuremath{\sim}0.77 to 0.86 in the studied temperature range; no change of activation energy, as suggested in previous reports, associated with liquid-liquid phase transition was observed. In contrast, the ${\mathrm{Ce}}_{70}{\mathrm{Cu}}_{19}{\mathrm{Al}}_{11}$ melt exhibits larger diffusivity with a much smaller activation energy of $0.201\ifmmode\pm\else\textpm\fi{}0.003\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$ and a smaller stretching exponent \ensuremath{\sim}0.51 to 0.60, suggestive of more heterogeneous dynamics.