How glasses relax at room temperature is still a great challenge for both experimental and simulation studies due to the extremely long relaxation time-scale. Here, by employing a modified molecular dynamics simulation technique, we extend the quantitative measurement of relaxation process of metallic glasses to room temperature. Both energy relaxation and dynamics, at low temperatures, follow a stretched exponential decay with a characteristic stretching exponent β = 3/7, which is distinct from that of supercooled liquid. Such aging dynamics originates from the release of energy, an intrinsic nature of out-of-equilibrium system, and manifests itself as the elimination of defects through localized atomic strains. This finding is also supported by long-time stress-relaxation experiments of various metallic glasses, confirming its validity and universality. Here, we show that the distinct relaxation mechanism can be regarded as a direct indicator of glass transition from a dynamic perspective.

The localized β-relaxation process is critical for understanding the complex dynamics and controlling the properties of glasses. However, the β-relaxation in most metallic glasses only appears in a form of excess wing or shoulder in dynamic mechanical spectra while the underlying mechanism of the β-relaxation remains elusive. In the present work, the β-relaxation of metallic glasses is systematically studied by calorimetry where the glass-transition temperature ($T_{\mathrm{g}}$) is resolved. The key finding is that the long-time sub-$T_{\mathrm{g}}$ annealing induces an endothermic peak upon heating prior to $T_{\mathrm{g}}$ with an activation energy of $\sim 26R{T}_{\mathrm{g}}$. By using an annealing-scanning-annealing thermal protocol, we show that this distinct endothermic sub-$T_{\mathrm{g}}$ peak is a reversible β-relaxation, indicating that the β-relaxation has both reversible and irreversible parts, which can be refined by the combination of calorimetry and the designed thermal protocol. The results might deepen our understanding of relaxation and the aging of metallic glasses.

Metallic glasses (MGs) that mainly made up of metallic elements are a new member of the glassy materials family. This new kind of glass combines the characteristics of liquids and solids, glasses and metals, making it fascinating to both scientists and industrialists. With the discovery of more and more systems, MG is becoming one of the most active research field in metallic materials, and some concepts and technologies derived from MGs also facilitate the development of other materials from quasi-crystals to high entropy alloys. MGs have now been successfully used in aerospace, robotics, medicine, consumer electronics, etc. and the practical applications of MGs are still growing. On the other hand, the diverse properties and the unique structure of the MGs render them ideal models to study major open issues including the structural model of disordered materials, glass transition, collective motion and energy landscape. However, understanding the emerging properties and phenomena of MGs still poses enormous challenges, which has stimulated a wealth of efforts, including the development of new experimental approaches, the synthesis of systems with tailored properties, and the advancements in experimental techniques, theoretical models, and numerical simulations. In this Roadmap, we try to provide a broad overview of recent and potential future activities in the MG field, and present a roadmap for the development and applications of MGs by gathering contributions form scientists with diverse backgrounds, illustrating the major challenges and discussing the latest technology and strategy to tackle these challenges with experts covering various developments in general concepts, synthesis and characterisation, and theoretical and simulation methods.

Carbon-doped GaAs and InP grown at low temperatures by molecular-beam epitaxy contain a high concentration of antisite defects which gives rise to ultrafast carrier trapping time and desirable radiation-hard properties. The use of CBr4 as the dopant source introduced significant bromine incorporation during low-temperature (LT) growth. Incomplete dissociation of the CBr4 molecules gives rise to the formation of C–Br complexes and results in a reduction of electrically active carbon concentration. In this work, we present our studies on the incorporation mechanism of C and Br in LT-GaAs and report on the effect of carbon and bromine incorporation on carrier lifetime and concentration of arsenic antisite defects. Preliminary results on LT-InP:C characterization are also presented.