Topological and chemical ordering in Co43Fe20Ta5.5B31.5 metallic glass

Atomic structure of Co43Fe20Ta5.5B31.5 metallic glass has been studied with x-ray and neutron diffraction, extended x-ray absorption fine structure experiments, and reverse Monte Carlo modeling. Each boron atom is found to have an average 2.3 nearest boron neighbors, which is significantly higher than in binary Co81.5B18.5 and Fe80B20 glasses. The existence of Ta-based structural units with the composition close to the stoichiometry of the (Co,Fe)(21)Ta2B6 crystalline phase precipitating upon annealing of the glass is established. Ta-B and B-B bonds, which are absent in the crystalline state, are suggested to be responsible for the high glass-forming ability and thermal stability of the Co43Fe20Ta5.5B31.5 glass.