Revisiting the Fragile-to-Strong Crossover in Metallic Glass-Forming Liquids: The Case of the Cu_xZr_xAl_100-2x Alloy

A reliable description of the dynamic properties of metallic glass-forming liquids is highly important for the understanding of the glass forming ability of these materials. To this end, we investigate the behavior of the dffusion coefficient, vibrational spectra, and shear viscosity of the Cu_xZr_xAl_100-2x alloy (for x= 50, 49, 46) through molecular dynamics simulations. The glass transition temperatures (T_g) we obtained for different compositions are in good agreement with both experimental and computational findings, indicating an increase of T_g with the amount of aluminum in the alloy. The inverse of the diffusion coefficient as a function of temperature shows a fragile-to-strong crossover at temperatures (T_fs) in the vicinity of T_g (730 K ≤ T_fs ≤ 797 K), which are significantly lower than previous estimates. These results are corroborated by the development of an excess of vibrational modes at temperatures just below T_fs. Shear viscosity as a function of T_g/T also displays the expected Arrhenius behavior below T_fs. Moreover, our results indicate another dynamic crossover related to the onset of dynamical heterogeneities at a temperature about 1200 K, which much higher than T_fs.