Dynamics in Cu46Zr42Al7Y5 melts: Interplay between packing density and viscosity

We have investigated microscopic dynamics in the bulk glass-forming Cu ₄₆Zr₄₂A_l7Y₅ melts using quasielastic neutron scattering (QENS). Self-correlation functions show a fast Β and a slow α -relaxation process. α relaxation exhibits stretching and is independent of momentum transfer and temperature. The melt is characterized by low packing density and high viscosity. The dynamics observed and the critical packing density derived from the QENS data are in good agreement with mode-coupling theory predictions for hard-sphere liquids. However, we can show that viscosity dominates over packing density in determining the atomic dynamics and glass-forming ability of the metallic melt. © 2009 American Institute of Physics.