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

Abstract

Secondary \ensuremath{\beta} 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 \ensuremath{\beta}-relaxation behaviors in ${\mathrm{Y}}_{60}{\mathrm{Ni}}_{16}{\mathrm{Al}}_{24}$ and ${\mathrm{Y}}_{60}{\mathrm{Fe}}_{16}{\mathrm{Al}}_{24}$ 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 \ensuremath{\beta} relaxation in ${\mathrm{Y}}_{60}{\mathrm{Ni}}_{16}{\mathrm{Al}}_{24}$ and ${\mathrm{Y}}_{60}{\mathrm{Fe}}_{16}{\mathrm{Al}}_{24}$ 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 $\ensuremath{\langle}0,3,6,0\ensuremath{\rangle}$ centered by Ni atoms into $\ensuremath{\langle}0,2,8,0\ensuremath{\rangle}$ 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 \ensuremath{\beta} 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 \ensuremath{\beta}-relaxation behaviors in MGs and other glassy materials from their local atomic environments and dynamics point of view.