The short-range ordered but long-range disordered structure of metallic glasses yields strong structural and dynamic heterogeneities. Stress relaxation is a technique to trace the evolution of stress in response to a fixed strain, which reflects the dynamic features phenomenologically described by the Kohlrausch-Williams-Watts (KWW) equation. The KWW equation describes a broad distribution of relaxation times with a small number of empirical parameters, but it does not arise from a particular physically motivated mechanistic picture. Here we report an anomalous two-stage stress relaxation behavior in a ${\mathrm{Cu}}_{46}{\mathrm{Zr}}_{46}{\mathrm{Al}}_8$ metallic glass over a wide temperature range and generalize the findings in other compositions. Thermodynamic analysis identifies two categories of processes: a fast stress-driven event with large activation volume and a slow thermally activated event with small activation volume, which synthetically dominates the stress relaxation dynamics. Discrete analyses rationalize the transition mechanism induced by stress and explain the anomalous variation of the KWW characteristic time with temperature. Atomistic simulations reveal that the stress-driven event involves virtually instantaneous short-range atomic rearrangement, while the thermally activated event is the percolation of the fast event accommodated by the long-range atomic diffusion. The insights may clarify the underlying physical mechanisms behind the phenomenological description and shed light on correlating the hierarchical dynamics and structural heterogeneity of amorphous solids.

It has so far remained a major challenge to quantitatively predict the boson peak, a THz vibrational anomaly universal for glasses, from features in the amorphous structure. Using molecular dynamics simulations of a model ${\mathrm{Cu}}_{50}{\mathrm{Zr}}_{50}$ glass, we decompose the boson peak to contributions from atoms residing in different types of Voronoi polyhedra. We then introduce a microscopic structural parameter to depict the “orientational order,” using the vector pointing from the center atom to the farthest vertex of its Voronoi coordination polyhedron. This order parameter represents the most probable direction of transverse vibration at low frequencies. Its magnitude scales linearly with the boson peak intensity, and its spatial distribution accounts for the quasilocalized modes. This correlation is shown to be universal for different types of glasses.

What determines the glass property remains one of the major unsolved problems in both condensed matter physics and materials science. Despite extensive research attempting to identify possible structural features as property signatures in glasses obeying the conventional philosophy of “structure determines property” in matter, the hidden rule about why some proposed structures predict properties effectively but others do not is still poorly understood. Here we revisit some earlier proposed successful “structural descriptors” in glasses, e.g., vibrational mean-squared displacement, flexibility volume, participation fraction of low-frequency vibrational modes, and two-body excess entropy, correlating them with the long-time dynamic property of model glass probed via the activation energy for local structural excitation. We find that all four structural descriptors correlate strongly with the activation energy, presenting large Pearson's correlation coefficients. By examining the spatial nature of the activation energy and the structural descriptors, a common rule for the robustness of structure–property relationships in glasses is established, according to which there exists a critical characteristic correlation length. We further demonstrate the concept that complex structures determine the glass property by manipulating the cutoff distance used to define the two-body excess entropy. Only if this structural descriptor is defined involving atoms beyond the first nearest neighbor does it reproduce the feature of common spatial correlation range in glass. The presence of a common spatial correlation length strongly indicates that it is necessary to include the spatial correlation of a complex structure accounting for the dynamic property of metallic glasses.

The slow transition from an out-of-equilibrium glass towards a supercooled liquid is a complex relaxation phenomenon. In this Letter, we study the correlation between mechanical relaxation and equilibration kinetics in a ${\text{Pd}}_{20}{\text{Pt}}_{20}{\text{Cu}}_{20}{\text{Ni}}_{20}{\mathrm{P}}_{20}$ high-entropy metallic glass. The evolution of stress relaxation with aging time was obtained with an unprecedented detail, allowing us to pinpoint new interesting features. The long structural relaxation towards equilibrium contains a wide distribution of activation energies, instead of being just associated to the $\beta$ relaxation as commonly accepted. The stress relaxation time can be correlated with the equilibration rate and we observe a decrease of microstructural heterogeneity which contrasts with an increase of dynamic heterogeneity. These results significantly enhance our insight of the interplay between relaxation dynamics and thermodynamics in metallic glasses.