Metallic glasses challenge the classical structure–property doctrine because the lack of long-range periodicity makes their structures complex and inherently multiscale. Although short-range order (SRO) within the first-neighbor cage has provided a useful vocabulary (e.g., icosahedral versus liquid-like motifs), growing evidence shows that SRO alone is not a reliable state variable for properties, such as stability and mechanical performance. In particular, the same nominal SRO motif can correspond to distinct energetic states depending on its embedding at more extended length scale, and local propensity indicators do not uniquely predict whether local plastic activity remains isolated or evolves into avalanches and extensive plastic deformation. We argue that rethinking glass structure requires shifting from per-atom SRO coordinates toward collective variables, defined over the range of relevant cooperativity. Within this framework, we clarify two kinds of medium-range order (MRO) that are frequently conflated in the literature at the intermediate scales (around second nearest- neighbor shell, 0.5–1 nm). One is the topological MRO, manifested as SRO motif connectivity/networking in atomistic models or as crystal-like nanodomains, probed by fluctuation electron microscopy and 4D-STEM. Another is defined by the persistent oscillations of pair distribution functions (i.e., the density wave fluctuations). Their coherence length is also about the same scale, and provides an alternative, more general view of the MRO. This motivates an energy landscape-based viewpoint in which density-fluctuation fields do not map to single basins, but condition the statistical accessibility of basins and activation barriers, thereby shaping the rigidity network that steers cascade propagation. We conclude by outlining quantitative opportunities to connect these scale-dependent collective descriptors, response-based diffraction, and energy landscape sampling into predictive, experimentally anchored structure–property relations. Data-driven atomistic analysis of metallic-glass structures using smooth overlap of atomic positions (SOAP) descriptors and transparent machine learning to identify radius of informative structural environments (RISE) Data-driven atomistic analysis of metallic-glass structures using smooth overlap of atomic positions (SOAP) descriptors and transparent machine learning to identify radius of informative structural environments (RISE)
Chemical short-range order (CSRO), the non-random local arrangement of atoms in solid solutions, strongly affects the phase stability and performance of medium- and high-entropy alloys (M/HEAs). Despite its importance, the fundamental nature of CSRO formation remains contested: is it a formal thermodynamic transition? Here, investigating CoCrNi as a model system, we indicate that the main CSRO transformations observed in alloys might not be classical thermodynamic transitions, but instead a kinetic arrest phenomenon analogous to the glass transition. Combining atomistic simulations and in situ synchrotron dilatometry experiments enabled the study of CSRO evolution and its structural impact across multiple length scales. For example, CSRO-driven changes in bond lengths and bond distribution significantly impact the observed lattice parameter and volume, allowing Warren-Cowley parameter values to be determined over a full experimental temperature range. We demonstrate that the degree of CSRO and the apparent transition temperatures, defined here as the komplex reaction temperatures (Tkr), are not intrinsic material constants. Rather, they are path-dependent quantities governed by thermal history and diffusional constraints, directly reflecting the frozen CSRO state. Our findings clarify the thermodynamic and kinetic mechanisms underlying CSRO evolution and establish a framework to distinguish thermodynamic transitions under kinetic constraints from genuine kinetically arrested phenomena. Understanding this distinction is crucial for controlling CSRO during alloy design and processing and provides a foundation for future investigations exploring the implications of CSRO in advanced materials. In situ synchrotron dilatometry and atomistic simulations indicate that changes between chemical short-range order states (evolving local chemical distributions) are governed by a kinetic arrest phenomenon rather than a thermodynamic transition.
G. C. Stumpf, Yifan Cao, V. Bacurau et al.· Nature Communications· 0 citations
Did you know that the strongest known engineering alloy is a metallic glass? This and many other world records have emerged along the success story of amorphous metals. With their unique structural and functional properties, and arising from a vast structural design space, metallic glasses are the amorphous counterpart to the high-entropy alloys paradigm. Sixty years after their discovery, metallic glasses have matured to industrial applications, but our structural understanding remains far behind. Presently, the advent of novel structural and dynamical probing methods, combined with new theoretical and modeling approaches, allow for the first time a one-to-one mapping of structure and structural dynamics. These developments emphasize medium-range order, extended network formation, and distinct structural partitioning in long-sought depth and detail for atomically disordered solids. Such a new view on metallic-glass microstructure and dynamics bears the promise of unifying numerous macroscopically observed phenomena, including negative creep, enthalpy recovery, stress-driven rejuvenation, and many more. This issue of MRS Bulletin aims at highlighting these advances, their promise to predictively understand macroscopic behavior, and to formulate reliable descriptors for structure and dynamics and for structure–property relationships of glassy materials. Metallic glasses are outstanding metallic alloys that combine the best properties from glassy solids and crystalline engineering alloys. This article introduces the current state-of-the-art and projects the future of structure and dynamics research of metallic glasses. As an overview article, it sets the stage for a series of subsequent focused contributions in this special issue Metallic glasses are outstanding metallic alloys that combine the best properties from glassy solids and crystalline engineering alloys. This article introduces the current state-of-the-art and projects the future of structure and dynamics research of metallic glasses. As an overview article, it sets the stage for a series of subsequent focused contributions in this special issue
The slow energy relaxation in quenched glasses is a ubiquitous yet poorly understood phenomenon. Despite extensive study, the microscopic origin of the observed power-law decay remains debated, with proposed mechanisms ranging from saddle-point slowdown and marginal stability to coarsening of localized excitations and phonon dynamics. Here, by simulating gradient descent in archetypal structural glass formers, we show that none of these scenarios can account for our data. Instead, the power-law behavior emerges from a remarkably simple caging effect: each particle experiences an effective stiffening potential that arises from many-body confinement and diverges at a characteristic cage size. This mechanism analytically yields the observed power-law decay and is quantitatively reproduced by a minimal single-particle cage model with fixed neighbours, demonstrating that collective relaxation modes are not essential. The dynamics is punctuated by fluctuations as the system rolls through inflection points on the energy landscape, which act as `speed bumps'but do not affect the overall power-law behaviour. In contrast to mean-field spin glass theory, we find no characteristic temperature that separates distinct dynamical regimes; state following within a given glass basin occurs universally for all initial temperatures whenever the system is sufficiently close to the inherent structure. Our results establish a complete physical picture of gradient descent dynamics in typical structural glasses.
Chemical short-range order (CSRO) is an intrinsic feature of complex concentrated alloys (CCAs), yet its influence on deformation mechanisms is controversial because of the inconclusive state of concurrent CSRO quantification during deformation. Here, we provide experimental evidence that CSRO acts as an intrinsic thermodynamic state variable governing stacking-fault energetics and deformation pathways in a Co30Cr40Ni30 alloy. By comparing quenched (CSRO-lean) and aged (CSRO-enriched) conditions with equivalent grain structure and phase constitution, we isolate the influence of atomic-scale chemical ordering on mechanical behavior. Calorimetry confirms reversible CSRO formation, while synchrotron X-ray diffraction and electron microscopy reveal that CSRO suppresses deformation-induced fcc-hcp martensitic transformation at both room and cryogenic temperatures. Despite differences in transformation dynamics, the macroscopic tensile response is still broadly similar. Atomistic simulations show that CSRO increases both stable and unstable stacking-fault energies, raising the energetic barrier for partial-dislocation activity and stabilizing the fcc lattice against transformation. Together, the experimental and computational results establish CSRO as an added degree of freedom for tuning stacking-fault energetics and controlling deformation pathways in complex concentrated alloys.
A. Andreoli, G. B. Ribeiro, G. C. Stumpf et al.· 0 citations
We analyze chemical short-range order in equiatomic fcc NiCoV using molecular-dynamics snapshots generated with a machine-learned interatomic potential. Radial distribution functions identify stable coordination shells, while shell-resolved Warren-Cowley parameters and bond probabilities reveal continued chemical ordering after the radial structure has largely converged. The dominant signal is V-V avoidance in the first shell and V-V enrichment in the second shell, consistent with an L1$_2$-like local ordering tendency, while the third-shell response remains weak. Lagged Jensen-Shannon diagnostics show that bond statistics relax more slowly than the RDF. Principal component analysis of per-replica-centered bond probabilities resolves three collective modes: a V-sublattice ordering amplitude, a Ni-Co redistribution mode, and a Co-V exchange-like mode. These results show that scalar RDF convergence can miss slow chemical relaxation, and that shell-resolved bond statistics provide a compact route for tracking SRO development in multicomponent alloys.
Electric fields can alter the orientational symmetry of liquid crystals, driving the emergence of biaxial order with potential relevance for next-generation electro-optical devices. Here, we present a coarse-grained (CG) model for a liquid crystal of board-like mesogens that enables a direct connection with our previous atomistic molecular dynamics simulations. The model is constructed through a particle-based mapping scheme that preserves the intrinsic anisotropy of the molecular core while enabling access to larger system sizes and longer time scales. Effective bonded and non-bonded interactions are obtained within a bottom-up force-matching framework and validated against atomistic reference data through structural and orientational correlations. A comparison with the atomistic reference allows us to assess both the capabilities and the limitations of the present CG representation, particularly in relation to the subtle balance between nematic and weak smectic-A organisation. Building on this framework, we then investigate the response of the system to externally applied electric fields. The model successfully captures field-induced reorientation dynamics and reveals a strong dependence of the ordering kinetics on field strength. Stronger fields substantially accelerate the evolution towards equilibrium, eventually leading to a rapid-alignment regime at high field strengths. After the field is removed, the system retains residual orientational memory rather than fully relaxing to its initial disordered state, suggesting persistent field-induced correlations that may affect subsequent switching processes. Most importantly, the external field promotes the formation of a biaxial nematic phase, highlighting the ability of the model to capture subtle symmetry-breaking phenomena induced under non-equilibrium conditions and relevant to electro-optical applications. The present CG model provides an efficient and physically consistent framework for exploring equilibrium structures, switching dynamics, and field-driven non-ordering in liquid-crystalline materials.
Adrián Díaz-Acosta, A. Gil-Villegas, Alessandro Patti· Soft Matter· 0 citations
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