Short-range order controlling atomic dynamics in Y-based metallic glasses

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Secondary {β} relaxation is considered a key issue in glassy materials, while its structural origin is still not well understood. In this paper, we report pronounced and unpronounced {β}-relaxation behaviors in Y₆₀Ni₁₆Al₂₄ and Y₆₀Fe₁₆Al₂₄ metallic glasses (MGs) obtained from dynamical mechanical analyses, respectively, despite the same composition and similar atomic sizes of Ni and Fe atoms. We elucidate that the {β} relaxation in Y₆₀Ni₁₆Al₂₄ and Y₆₀Fe₁₆Al₂₄ MGs mainly depends on the vibration of small Ni and Fe atoms using synchrotron x-ray techniques and theoretical calculations, respectively. From the x-ray absorption fine structure and Voronoi tessellation statistics, it is found that the dominant local structure of mobile atoms changes from 0,3,6,0 centered by Ni atoms into 0,2,8,0 centered by Fe atoms. More large Y atoms in shells promote the local vibration of center Ni atoms. In contrast, with more Y atoms replaced by Fe atoms, the vibration of center Fe atoms gets significantly slowed down, thus leading to an unpronounced {β} relaxation. Our results indicate that the atomic dynamics of mobile atoms in MGs are not only related to their surrounding local geometry but also chemical constitutions, i.e., the short-range order. In this paper, we provide an idea for understanding the structural origin of {β}-relaxation behaviors in MGs and other glassy materials from their local atomic environments and dynamics point of view.