Atomic‐Level Structural Characteristics of <i>β</i> ‐Relaxation in Metallic Glasses

The β-relaxation is one of the crucial relaxation modes in glasses, which significantly influences their mechanical properties, structural heterogeneity, and glass transition. However, due to detection limitations, the β-relaxation has not been fully characterized and understood. In this work, in situ synchrotron radiation X-ray diffraction and absorption techniques are utilized to track the β-relaxation during heating and find that it can be reflected in the evolution of cluster structures within the first shells of metallic glasses. Through molecular dynamics simulations, it is further demonstrated that the β-relaxation is also well consistent with fast atomic motions linked with specific Voronoi polyhedra and chemical constitutions characterized by more excess free volume. The cyclic heating experiments provide evidence for the "irreversible" β-relaxation, which involves an event that is decayed during the sub-T_g annealing; however, it can be reactivated by subsequent high temperature rejuvenation. The discovery paves a new pathway for the study of β-relaxation, unveiling the origin of β-relaxation based on experimental and theoretical structural analysis methods.