Topological and chemical ordering in Co₄₃Fe₂₀Ta_5.5B_31.5 metallic glass

Atomic structure of Co₄₃Fe₂₀Ta_5.5B_31.5 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 Co_81.5B_18.5 and Fe₈₀B₂₀ glasses. The existence of Ta-based structural units with the composition close to the stoichiometry of the (Co,Fe)₂₁Ta₂B₆ 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 Co₄₃Fe₂₀Ta_5.5B_31.5 glass.