Roles of local icosahedral chemical ordering in glass and quasicrystal formation in metallic glass formers

It is well known that bulk metallic glass formers have a tendency to show local icosahedral chemical ordering. We argue that the frustration between this short-range bond ordering and the long-range crystalline ordering controls the fragility and the glass-forming ability of these liquids. Our model suggests that a system having a stronger tendency to show local icosahedral ordering should be less fragile and a better glass former. This scenario also naturally explains the close relationship among the degree of local icosahedral ordering in liquid, glass formability, and quasicrystal formability.