Atomic dynamics of metallic glass melts La50Ni15Al35 and Ce70Cu19Al11 studied by quasielastic neutron scattering

Abstract

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.