Relationship of the atomic dynamics and excess volume of a copper rich Cu76Ti24 alloy melt

We investigate the atomic dynamics of a Cu-rich Cu76Ti24 alloy between 1223 K and 1453 K using the quasi-elastic neutron scattering technique. The obtained mean Cu/Ti self-diffusion coefficient D exhibits an Arrhenius-like temperature dependence with an activation energy of 0.46�0.02 eV per atom. Compared with those of the pure elements at a given temperature, D is slower than that for pure Cu, but similar to pure Ti. This slowing down of the liquid dynamics upon alloying has been observed for most binary alloy systems. However, in this study, the packing fraction of the Cu-Ti alloy is lower than that of the pure elements, which can be explained by the positive excess volume of the Cu-Ti system. Therefore, the compositional dependence of the atomic dynamics cannot be linked to a macroscopic packing argument. Only, the atomic dynamics is not correlated with an increase of the average packing fraction of the melt.