Ab initio study on the electronic origin of glass-forming ability in the binary Cu-Zr and the ternary Cu-Zr-Al(Ag) metallic glasses

It is believed that the basic local cluster in metallic glasses (MGs) is the key to understand the origin of glass-forming ability (GFA) of MGs. Our ab initio simulations on the basic cluster in the binary Cu-Zr MGs as well as in the ternary Cu-Zr-Al(Ag) MGs provide the most straightforward evidence that the electronic stability of the basic cluster in MGs is the origin of the GFA. Our calculations reveal that the stability of the basic cluster is determined by its electronic states near the Fermi level. For the basic clusters in the best glass formers of Cu-Zr MGs, a gap near Fermi level is observed, indicating the stability of the basic clusters. With substitution of one Al(Ag) atom into the basic cluster in Cu50Zr50 MGs, a strong sp-d coupling of Al(Ag) with Cu and Zr is observed, which results in a stronger bonding and thus more stability of the basic cluster. Our findings provide a check for the atomic structural models proposed over the years for MGs, and have implications for understanding the formation and properties of MGs.