Stokes-Einstein relation in dense metallic glass-forming melts

Quasielastic neutron scattering has been used to investigate atomic motion in a very fragile binary metallic melt and a multicomponent bulk glass-forming metallic melt. Both melts show a breakdown of the Stokes-Einstein relation and display a change in the slope of In D dependence on In (eta/T). We also observed that the values for the exponent in the fractional Stokes-Einstein relation are not in the commonly observed range for Cu(46)Zr(42)Al(7)Y(5) melts. At low temperatures, the deviation from the Stokes-Einstein law is very significant and can be expressed in the form of a power law with exponent xi=-1.82 +/- 0.08. The change in the slope is found to be associated with a change in friction coefficient while increasing the packing density of the melt. The abrupt change in the value of friction coefficient is independent of packing density, but it occurs at a common value of zeta=(3.2 +/- 0.1) X 10(-12) kg s(-1) in these melts. (C) 2010 American Institute of Physics. [doi:10.1063/1.3523361]