Relaxation Time Scales Research Articles

Silicon Hysteresis and Voltage Relaxation Phenomena: Implications on Overpotential Analysis

Currently, many strategies are being developed to enable a successful implementation of silicon anode active material into commercial lithium-ion cells with the goal of increasing their specific capacities and energy densities. Compared to the commonly used graphite active material, silicon gives rise to a number of challenges owing to its large voltage hysteresis. Next to a decrease in energy efficiency and a significant corresponding heat evolution during cycling,1 the path-dependency of the potential and the resulting ambiguous voltage vs. SOC correlation complicates the development of battery control systems. While the origin of the voltage hysteresis is not yet fully understood, several studies suggest that it can, to a large part, be explained by compressive and tensile stress on the silicon material induced by its lithiation and delithiation respectively.2, 3 Another hysteresis effect which may also be explained by changes in mechanical stress is the unusual voltage relaxation of silicon at open-circuit voltage (OCV) conditions: the voltage undergoes significant changes at open-circuit and the voltage relaxation is still significant over extended periods of time.4 The implications of this voltage relaxation/hysteresis behavior on the commonly used experimental methods for the analysis of overpotentials (EIS, GITT, DCIR) have, to the best of our knowledge, not been analyzed in the literature.In this study we characterize the hysteresis and voltage relaxation behavior of a silicon-dominant electrode containing 70 wt% micro-scale silicon particles (Wacker Chemie AG) for which the amorphous silicon fraction is reversibly lithiated to the composition Li2Si (reversible capacity: 1200 mAh/gSi).5, 6 We find an offset of ~60 mV between the voltage after a 2 h OCV phase compared to the voltage at a very slow rate of C/20, which is surprisingly large compared to the voltage differences observed between different C-rates (e.g., ~10 mV between C/20 and C/2, see Fig. 1). This suggests that a form of structural relaxation may occur in the silicon material once there is no ongoing (de-)lithiation. As a result of this, the offset between the potential under load and at open-circuit cannot be used to calculate a resistance or a diffusion coefficient, as would typically be done for other active materials.7 By comparing charge/discharge potential curves recorded at different C-rates for thin silicon electrodes (1.0 mAh/cm2), effective cell resistances are estimated. Based on these results, methods used for the characterization of the kinetics of silicon are critically analyzed for their significance. We compare galvanostatic impedance (GEIS) measurements performed under load to potentiostatic impedance (PEIS) measurements performed at OCV. Further, we compare ΔE/ΔI values calculated at different points in time after the current has been turned off or on in order to analyze the impact and time-scale of the current-independent OCV relaxation. All results are compared to the same measurements performed for a graphite electrode. We ultimately show that the analysis of overpotentials of silicon active materials, when done incorrectly, can yield parameters which are physically meaningless and misleading for the characterization of the kinetics of silicon electrodes. Acknowledgements We gratefully acknowledge the German Federal Ministry of Education and Research (BMBF) for its financial support within the AQua HysKaDi project (03XP0321B). We also thank Wacker Chemie AG for kindly providing the silicon material. References V. L. Chevrier, Z. Yan, S. L. Glazier, M. N. Obrovac and L. J. Krause, 168, 030504 (2021).V. A. Sethuraman, V. Srinivasan, A. F. Bower and P. R. Guduru, 157, A1253 (2010).B. Lu, Y. Song, Q. Zhang, J. Pan, Y.-T. Cheng and J. Zhang, Physical chemistry chemical physics : PCCP, 18(6), 4721–4727 (2016).K. Pan, F. Zou , M. Canova and Y. Zhu, 413, 20-28 (2019).D. Jantke, R. Bernhard, E. Hanelt, T. Buhrmester, J. Pfeiffer, and S. Haufe, 166(16), A3881 (2019).M. Graf, C. Berg, R. Bernhard, S. Haufe, J. Pfeiffer and H. A. Gasteiger, 169(2), 020536 (2022).D. W. Dees, S. Kawauchi, D. P. Abraham, and J. Prakash, 189, 263-268 (2009). Figure 1 Silicon electrode potentials measured against a lithium reference electrode in a half-cell (Swagelok® T-cell setup) plotted against the estimated composition of lithium in the amorphous silicon fraction. (De-)lithiation potentials are shown for the C-rates of C/20 and C/2 and are compared to potentials recorded after 2 hours at OCV. The gray inset shows the offset between the two C-rates and the OCV at the estimated composition of ~Li1Si. Loading: 0.8 mgSi/cm2; areal capacity: 1.0 mAh/cm2; electrolyte: 1M LiPF6 in FEC/DEC (2:8 v:v); separator: two glassfiber separators (VWR); cycling: CC capacity limited lithiation, CCCV delithiation to 1.0 V. Figure 1

Few-body hydrodynamic interactions probed by optical trap pulling experiment.

We study the hydrodynamic coupling of neighboring micro-beads placed in a multiple optical trap setup allowing us to precisely control the degree of coupling and directly measure time-dependent trajectories of entrained beads. We performed measurements on configurations with increasing complexity starting with a pair of entrained beads moving in one dimension, then in two dimensions, and finally a triplet of beads moving in two dimensions. The average experimental trajectories of a probe bead compare well with the theoretical computation, illustrating the role of viscous coupling and setting timescales for probe bead relaxation. The findings also provide direct experimental corroborations of hydrodynamic coupling at large, micrometer spatial scales and long, millisecond timescales, of relevance to, e.g., microfluidic device design and hydrodynamic-assisted colloidal assembly, improving the capability of optical tweezers, and understanding the coupling between micrometer-scale objects within a living cell.

A large deformation model for quasi-static to high strain rate response of a rate-stiffening soft polymer

Polyborosiloxane (PBS) is an important rate-stiffening soft polymer with dynamic, reversible crosslinks used in applications ranging from self-healing sensing and actuation to body and structural protection. Its highly rate-dependent response, especially for impact-mitigating structures, is important. However, the large strain response of PBS has not been characterized over quasi-static to high strain rates. Currently, there are no constitutive models that can predict the strongly rate-dependent large-deformation elastic-viscoplastic response of PBS. To address this gap, we have developed a microstructural physics motivated constitutive model for PBS, similar soft polymers and polymer gels with dynamic crosslinks to predict their large strain, non-linear loading–unloading, and significantly rate-dependent response. We have conducted compression experiments on PBS up to true strains of ∼125% and over a wide strain rate range of 10−3 s−1 to 103 s−1. The proposed semi-physical model fairly accurately captures the response of PBS over six decades of strain rates. We propose boron–oxygen coordinate-bond dynamic crosslinks with macroscopic relaxation timescale τ≈3 s and temporary entanglement lockups at high strain rates acting as crosslinks with τ≈0.0005 s as the two types of crosslink network mechanisms in PBS. We have outlined a numerical update procedure to evaluate the convolution-like time integrals arising from dynamic crosslink kinetics. Experiments involving three-dimensional inhomogeneous deformations were used to verify the predictive capabilities of our model and its finite element implementation. The modeling framework can be adopted for other dynamically crosslinked rate-stiffening soft polymers and polymer gels that are microstructurally similar to PBS.

Unveiling the Rheological Control of Magmatic Systems on Volcano Deformation: The Interplay of Poroviscoelastic Magma‐Mush and Thermo‐Viscoelastic Crust

AbstractUnderstanding the mechanical evolution of magmatic systems requires careful assessment of their rheological characteristics, particularly in light of the growing evidence that magma reservoirs are dominated by magma‐mush surrounded by thermally‐altered host‐rock. To address this complexity, we develop models for volcano deformation based on a poroviscoelastic source within a thermo‐viscoelastic host. We use Finite Element modeling to investigate the rheological and mechanical response to melt injection in a Maxwell poroviscoelastic reservoir hosted in a temperature‐dependent standard linear solid viscoelastic (“thermo‐viscoelastic”) crust. Our models consider the competing roles of poroelastic diffusion, and viscoelastic creep and relaxation. All cause time‐dependent post‐injection deformation. Post‐injection deformation of a poroviscoelastic reservoir in an elastic crust is dominated by poroelastic diffusion, a consequence of the short relaxation timescale of a hot and relatively low viscosity mush. For cooler, more viscous mush, the magnitude of viscoelastic deformation increases, supplementing the deformation caused by post‐injection poroelastic diffusion. Thermo‐viscoelasticity of the crust amplifies the poroelastic deformation response of the magma‐mush, leading to increased time‐dependent deformation both during and after melt injection. The rate of post‐injection surface deformation decreases at a rate proportional to the reservoir temperature. Crucially, our model sensitivity analysis demonstrates that the wall rock thermo‐viscoelastic response contributes more to surface deformation than the viscous effect of the magma‐mush. For this reason, neglecting the viscoelastic properties of the host rock and the poroelastic properties of the reservoir in interpretations of surface deformation data could produce errors in inferred processes (e.g., injection duration) and subsurface characteristics (e.g., reservoir compressibility, shape and depth).

Stochastic motion and transcriptional dynamics of pairs of distal DNA loci on a compacted chromosome.

Chromosomes in the eukaryotic nucleus are highly compacted. However, for many functional processes, including transcription initiation, the pairwise motion of distal chromosomal elements such as enhancers and promoters is essential and necessitates dynamic fluidity. Here, we used a live-imaging assay to simultaneously measure the positions of pairs of enhancers and promoters and their transcriptional output while systematically varying the genomic separation between these two DNA loci. Our analysis reveals the coexistence of a compact globular organization and fast subdiffusive dynamics. These combined features cause an anomalous scaling of polymer relaxation times with genomic separation leading to long-ranged correlations. Thus, encounter times of DNA loci are much less dependent on genomic distance than predicted by existing polymer models, with potential consequences for eukaryotic gene expression.

Exploring the Heterogeneous Dynamical Environment at the Interface of Aβ42 Peptide in Aqueous Ionic Liquid Solution.

In this study, we have investigated the heterogeneous dynamical environment around an ensemble of full-length amyloid-β (Aβ42) peptide monomers in binary aqueous solution containing the ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM][BF4] as a co-solvent. Atomistic molecular dynamics (MD) simulations have been employed with the aim of understanding the effect of the IL on the distribution of water molecules and IL components around distinct segments of the peptide. As compared to pure aqueous medium, locally heterogeneous restricted water motions at the interface have been spotted in the presence of the IL. Our calculations revealed faster diffusion of water molecules hydrating hydrophilic segments (N-term and turn) as opposed to that around hydrophobic segments (hp1, hp2, and C-term). The extent of non-uniform restriction on the center-of-mass motions as well as the reorientation of water molecules and IL ions have been similarly affected in the binary IL-water solution. The effects of IL on the formation of hydrogen bond networks have been evident from the longer hydrogen bond relaxation time scales of peptide-water, with only a small fraction of peptide-anion hydrogen bonds contributing to the structural relaxation. Due to the size and shape factors, the increasingly sluggish dynamics of the IL components in the solvation shell can be attributed to a longer time scale for the onset of maximum dynamic heterogeneity. Interestingly, the water molecules around the polar segments of the peptide take longer to attain dynamic heterogeneity, which intensifies in the presence of IL. These calculations clearly suggest that electrostatic interaction plays a crucial role in water-mediated peptide-IL interaction, thereby shielding the surface from hydrophobic collapse and preventing possible further growth of the monomers into fibrils at higher peptide concentrations.

Cohesion and aggregates in unsaturated wet granular flows down a rough incline

Multi-phase flows, encountered in nature or in industry, exhibit non-trivial rheological properties, which we attempt to better understand thanks to model materials and appropriate rheometers. Unsaturated wet granular flows down a rough inclined plane turn out to be steady and uniform for a wide range of parameters, despite the cohesion and the grain aggregates. The cohesive Mohr–Coulomb yield criterion extended to inertial granular flows, with a cohesion stress dependent on the liquid content and an internal friction coefficient dependent on the inertial number, allows for predictions in good agreement with our experimental measurements, when one introduces a grain aggregate size, which defines the appropriate length and relaxation time scales in the inertial number. We found that the grain aggregate size depends not monotonically on the liquid content and does not scale with the cohesion length induced by the cohesion stress, due to the non-trivial distribution of the liquid within the granular material.

Water hydration of polyethylene glycol dimethyl ether.

In this work, GHz and THz complex dielectric spectra of a polyethylene glycol dimethyl ether (2000 g/mol) aqueous solution were studied. The reorientation relaxation of water in this kind of macro-amphiphilic molecule solution can be well described by three Debye models, including under-coordinated water, bulk-like water [water molecules in a tetrahedral hydrogen bond network (bulk water) and bulk water molecules affected by hydrophobic groups], and slow hydrating water (water molecules donating hydrogen bonds to hydrophilic ether groups). The reorientation relaxation timescales of bulk-like water and slow hydration water both show increases with concentration from 9.8 to 26.7ps and from 46.9 to 100.1ps, respectively. By estimating the ratios of the dipole moment of slow hydration water to the dipole moment of bulk-like water, we calculated the experimental Kirkwood factors of bulk-like and slow hydrating water. The experimental Kirkwood factor of bulk-like water increased from 3.17 to 3.44 with concentrations, while the experimental Kirkwood factor of slow hydrating water roughly remained constant at 4.13 from concentrations of 15%-60%. The estimated water molecule numbers of three water components around monomers also confirm our sorting for water components.

Non‐Synchronous Rotation on Europa Driven by Ocean Currents

AbstractIt has been suggested that the ice shell of Jupiter's moon Europa may drift non‐synchronously due to tidal torques. Here we argue that torques applied by the underlying ocean are also important and can result in non‐synchronous rotation. The resulting spin rate can be slightly slower than the synchronous angular rate that would have kept the same point of the ice shell facing Jupiter. We develop an ice shell rotation model, driven by ocean stress calculated using a high‐resolution state‐of‐the‐art ocean general circulation model, and take into account the viscoelastic deformation of the ice shell. We use the ice shell model results together with observed limits on the ice shell drift speed to constrain ice shell parameters such as effective viscosity, which is currently uncertain by at least four orders of magnitude. Our results suggest, at best, sluggish ice shell convection. Depending on the relaxation time scale of the ice shell and on the ocean currents, the ice shell may exhibit negligible drift, constant drift, or oscillatory drift superimposed on random fluctuations. The expected rotation rate exceeds ∼30 m/yr; future spacecraft observations can be used to test these predictions and yield insight into the properties of the ice shell and underlying ocean.

Pulsatory patterns in active viscoelastic fluids with distinct relaxation time scales

Developing tissues need to pattern themselves in space and time. A prevalent mechanism to achieve this are pulsatile active stresses generated by the actin cytoskeleton. Active gel theory is a powerful tool to model the dynamics of cytoskeletal pattern formation. In theoretical models, the influence of the viscoelastic nature of the actin cytoskeleton has so far only been investigated by the incorporation of one viscoelastic relaxation time scale. Here, using a minimal model of active gel theory, we show that distinct shear and areal relaxation times are sufficient to drive pulsatile dynamics in active surfaces with only a single molecular regulator.

Linear response hydrodynamics of a relativistic dissipative fluid with spin

We formulate a Lagrangian hydrodynamics including shear and bulk viscosity in the presence of spin density, and investigate it using the linear response functional formalism. The result is a careful accounting of all sound and vortex interactions close to local equilibrium. In particular, we demonstrate that the mixing of sound waves and vortices via polarization, first observed in the ideal fluid limit, extends to the shear mode once dissipative effects are included. This provides a realization within Lagrangian hydrodynamics of the symmetric shear polarization contribution recently advocated from transport and Zubarev approaches as well as phenomenological considerations. Once causal relaxational dynamics is included, this effect, seemingly puzzling because it results in a nondissipative coupling between a transient mode to an equilibrium quantity, can be understood as a competition between the Israel-Stewart and the polarization relaxation timescale, and a breakdown of local Markovianity. We close by discussing phenomenological implications of these results.

Nucleation and growth of crystalline ices from amorphous ices.

We here review mostly experimental and some computational work devoted to nucleation in amorphous ices. In fact, there are only a handful of studies in which nucleation and growth in amorphous ices are investigated as two separate processes. In most studies, crystallization temperatures Tx or crystallization rates RJG are accessed for the combined process. Our Review deals with different amorphous ices, namely, vapor-deposited amorphous solid water (ASW) encountered in many astrophysical environments; hyperquenched glassy water (HGW) produced from μm-droplets of liquid water; and low density amorphous (LDA), high density amorphous (HDA), and very high density amorphous (VHDA) ices produced via pressure-induced amorphization of ice I or from high-pressure polymorphs. We cover the pressure range of up to about 6GPa and the temperature range of up to 270K, where only the presence of salts allows for the observation of amorphous ices at such high temperatures. In the case of ASW, its microporosity and very high internal surface to volume ratio are the key factors determining its crystallization kinetics. For HGW, the role of interfaces between individual glassy droplets is crucial but mostly neglected in nucleation or crystallization studies. In the case of LDA, HDA, and VHDA, parallel crystallization kinetics to different ice phases is observed, where the fraction of crystallized ices is controlled by the heating rate. A key aspect here is that in different experiments, amorphous ices of different "purities" are obtained, where "purity" here means the "absence of crystalline nuclei." For this reason, "preseeded amorphous ice" and "nuclei-free amorphous ice" should be distinguished carefully, which has not been done properly in most studies. This makes a direct comparison of results obtained in different laboratories very hard, and even results obtained in the same laboratory are affected by very small changes in the preparation protocol. In terms of mechanism, the results are consistent with amorphous ices turning into an ultraviscous, deeply supercooled liquid prior to nucleation. However, especially in preseeded amorphous ices, crystallization from the preexisting nuclei takes place simultaneously. To separate the time scales of crystallization from the time scale of structure relaxation cleanly, the goal needs to be to produce amorphous ices free from crystalline ice nuclei. Such ices have only been produced in very few studies.

Magnetic field induced deformation of the spin density wave microphases in Ca3Co2O6

The frustrated triangular Ising magnet Ca$_3$Co$_2$O$_6$ has long been known for an intriguing combination of extremely slow spin dynamics and peculiar magnetic orders, such as the evenly-spaced non-equilibrium metamagnetic magnetization steps and the long-wavelength spin density wave (SDW) order, the latter of which is essentially an emergent crystal of solitons. Recently, an elaborate field-cooling protocol to bypass the low-field SDW phase was proposed to overcome the extraordinarily long timescale of spin relaxation that impeded previous experimental studies in equilibrium, which may point to a deep connection between the low-temperature slow relaxation and the cooling process passing through the low-field SDW phase. As the first step to elucidate the conjectured connection, we investigate the magnetic field-induced deformation of the SDW state and incommensurate-commensurate transitions, thereby mapping out the equilibrium in-field phase diagram for a realistic three-dimensional lattice spin model by using Monte Carlo simulations. We also discuss Ginzburg-Landau theory that includes several Umklapp terms as well as an effective sine-Gordon model, which can qualitatively explain the observed magnetic field-induced deformation of the SDW microphases.

Tuning the conductance topology in solids

The inertia of trapping and detrapping of nonequilibrium charge carriers affects the electrochemical and transport properties of both bulk and nanoscopic structures in a very peculiar way. An emerging memory response with hysteresis in the current–voltage response and its eventual multiple crossing, produced by this universally available ingredient, are signatures of this process. Here, we deliver a microscopic and analytical solution for these behaviors, understood as the modulation of the topology of the current–voltage loops. Memory emergence thus becomes a characterization tool for intrinsic features that affect the electronic transport of solids such as the nature and number of trapping sites, intrinsic symmetry constraints, and natural relaxation time scales. This method is also able to reduce the seeming complexity of frequency-dependent electrochemical impedance and cyclic voltammetry observable for a variety of systems to a combination of simple microscopic ingredients.

Significance of the nature of disorder on the universal features of the spatio-temporal correlations of two-dimensional Coulomb-clusters

We comprehend the role of imperfections in materials consisting of interacting particles, arising from different origins on their universal features. Specifically, we report the static and dynamic responses in a cluster of Coulomb interacting particles in two dimensions. Confined systems with pinned impurities are studied, and results are compared with those from irregularly trapped system of particles. While the disorder of first type leads to diffusive single-particle dynamics, the motion of a single particle in an irregular trap is chaotic but ballistic. The many-particle system does not differentiate between these two models of disorder insofar as their qualitative properties are concerned -- particularly for describing the thermal melting of the underlying Coulomb-"solid". However, quantitative differences persist -- the relaxation time scales differ significantly by tuning impurity concentration.

Constraint Release Rouse Mechanisms in Bidisperse Linear Polymers: Investigation of the Release Time of a Short-Long Entanglement

Despite a wide set of experimental data and a large number of studies, the quantitative description of the relaxation mechanisms involved in the disorientation process of bidisperse blends is still under discussion. In particular, while it has been shown that the relaxation of self-unentangled long chains diluted in a short chain matrix is well approximated by a Constraint Release Rouse (CRR) mechanism, there is no consensus on the value of the average release time of their entanglements, τobs, which fixes the timescale of the CRR relaxation. Therefore, the first objective of the present work is to discuss the different approaches proposed to determine this time and compare them to a large set of experimental viscoelastic data, either newly measured (poly(methyl-)methacrylate and 1,4-polybutadiene blends) or coming from the literature (polystyrene and polyisoprene blends). Based on this large set of data, it is found that with respect to the molar mass of the short chain matrix, τobs follows a power law with an exponent close to 2.5, rather than 3 as previously proposed. While this slight change in the power law exponent does not strongly affect the values of the constraint release times, the results obtained suggest the universality of the CRR process. Finally, we propose a new description of τobs, which is implemented in a tube-based model. The accurate description of the experimental data obtained provides a good starting point to extend this approach to self-entangled binary blends.

Quantum critical dynamics in the two-dimensional transverse Ising model

In the vicinity of the quantum critical point (QCP), thermodynamic properties diverge toward zero temperature governed by universal exponents. Although this fact is well known, how it is reflected in quantum dynamics has not been addressed. The QCP of the transverse Ising model on a triangular lattice is an ideal platform to test the issue, since it has an experimental realization, the dielectrics being realized in an organic dimer Mott insulator, $\ensuremath{\kappa}\text{\ensuremath{-}}{\mathrm{ET}}_{2}X$, where a quantum electric dipole represents the Ising degrees of freedom. We track the Glauber-type dynamics of the model by constructing a kinetic protocol based on the quantum Monte Carlo method. The dynamical susceptibility takes the form of the Debye function and shows a significant peak narrowing in approaching a QCP due to the divergence of the relaxation timescale. It explains the anomaly of dielectric constants observed in the organic materials, indicating that the material is very near the ferroelectric QCP. We disclose how the dynamical and other critical exponents develop near QCP beyond the simple field theory.

Relaxation time scales of interfacial water upon fluid to ripple to gel phase transitions of bilayers.

The slow relaxation of interface water (IW) across three primary phases of membranes is relevant to understand the influence of IW on membrane functions at supercooled conditions. To this objective, a total of ∼16.26μs all-atom molecular dynamics simulations of 1,2-dimyristoyl-sn-glycerol-3-phosphocholine lipid membranes are carried out. A supercooling-driven drastic slow-down in heterogeneity time scales of the IW is found at the fluid to the ripple to the gel phase transitions of the membranes. At both fluid-to-ripple-to-gel phase transitions, the IW undergoes two dynamic crossovers in Arrhenius behavior with the highest activation energy at the gel phase due to the highest number of hydrogen bonds. Interestingly, the Stokes-Einstein (SE) relation is conserved for the IW near all three phases of the membranes for the time scales derived from the diffusion exponents and the non-Gaussian parameters. However, the SErelation breaks for the time scale obtained from the self-intermediate scattering functions. The behavioral difference in different time scales is universal and found to be an intrinsic property of glass. The first dynamical transition in the α relaxation time of the IW is associated with an increase in the Gibbs energy of activation of hydrogen bond breaking with locally distorted tetrahedral structures, unlike the bulk water. Thus, our analyses unveil the nature of the relaxation time scales of the IW across membrane phase transitions in comparison with the bulk water. The results will be useful to understand the activities and survival of complex biomembranes under supercooled conditions in the future.

Prominent β-relaxation and stress relaxation decoupling phenomenon in Gd-Ni-Al metallic glasses

GdxNi20Al80−x (x = 50, 60, 65, 70 at%) metallic glasses (MGs) with prominent β-relaxation were developed, which provide a new model system for studying some controversial issues concerning β-relaxation. The relaxation behavior and thermal stability of GdxNi20Al80−x MGs were probed by dynamic mechanical relaxation, static stress relaxation, and differential scanning calorimetry. In view of the temperature and frequency dependence of the dynamic mechanical relaxation spectrum, we investigated the β-relaxation and α-relaxation separation phenomena of Gd50Ni20Al30 and Gd60Ni20Al20 MGs. With increasing Gd/Al ratio, the activation energy of the β-relaxation decreased, which was conducive to the flow units and prominent β-relaxation. The Gd70Ni20Al10 alloy had the most significant β-relaxation phenomenon, although some nanocrystalline Gd3Ni phase was distributed in the amorphous matrix. The Gd50Ni20Al30 glass had a crystallization activation energy of 476 kJ/mol, corresponding to the highest thermal stability. At a constant strain, the static stress relaxation process of the Gd70Ni20Al10 alloy was analyzed over a wide time window and temperature range. A decoupling phenomenon of the relaxation into a two-step process occurred in the Gd70Ni20Al10 alloy, namely, a fast relaxation process and a slow relaxation process, at different time scales. Analysis of the relaxation dynamics and time scales of the relaxation confirmed that the fast relaxation process differed from the β-relaxation process. This study elucidates the β-relaxation behavior and stress relaxation decoupling phenomenon in Gd-Ni-Al MGs and should, therefore, help clarify the mechanical relaxation behavior and intrinsic characteristics of MGs in future work.

Predicting timescales of relaxation in the shallow Earth’s subsurface

Earthquakes introduce long-lasting transient mechanical damage in the subsurface, which cause postseismic hazards such as enhanced landsliding and can take years to recover to steady-state values. This observation has been linked to relaxation, a phenomenon observed in a wide class of materials after straining perturbations. In this presentation, I analyze the successive effect of two large earthquakes on ground properties through the monitoring of seismic velocity from ambient noise interferometry in the Atacama desert in Chile. The absence of rainfall in this area allows study of the mechanical state of the subsurface by limiting the potential effect of variable groundwater content. I show that relaxation timescales are a function of the current state of the subsurface when perturbed by earthquakes, rather than ground shaking intensity. Our study highlights the predictability of earthquake damage dynamics in the Earth's near-surface and potentially other materials. I propose to reconcile this paradigm with existing physical frameworks by considering the superposition of different populations of damaged contacts.