Fragile-to-strong Research Articles

Relating fragile-to-strong transition to fragile glass via lattice model simulations.

Glass formers are, in general, classified as strong or fragile depending on whether their relaxation rates follow Arrhenius or super-Arrhenius temperature dependence. There are, however, notable exceptions, such as water, which exhibit a fragile-to-strong (FTS) transition and behave as fragile and strong, respectively, at high and low temperatures. In this work, the FTS transition is studied using a distinguishable-particle lattice model previously demonstrated to be capable of simulating both strong and fragile glasses [C.-S. Lee, M. Lulli, L.-H. Zhang, H.-Y. Deng, and C.-H. Lam, Phys. Rev. Lett. 125, 265703 (2020)0031-900710.1103/PhysRevLett.125.265703]. Starting with a bimodal pair-interaction distribution appropriate for fragile glasses, we show that by narrowing down the energy dispersion in the low-energy component of the distribution, a FTS transition is observed. The transition occurs at a temperature at which the stretching exponent of the relaxation is minimized, in agreement with previous molecular dynamics simulations.

An intrinsic connection between the liquid-liquid transition and fragile-to-strong transition in soft magnetic Fe-based metallic glasses: Comparisons with other metallic glasses

There are two significant abnormal transitions observed in metallic glass forming liquids (MGFLs), i.e., liquid-liquid transition (LLT) above liquidus temperature and fragile-to-strong (F-S) transition in supercooled region. In this study, we focus on the correlation between LLT and F-S transition in Fe-based soft magnetic metallic glasses (MGs) for the first time. We find that the more distinct the LLT is, the weaker is the F-S transition, and the smaller is the glass forming ability (GFA). By employing molecular dynamics simulation, we identify that this relationship is due to the inherent correlated evolution trends of crystal-like clusters between the LLT and the F-S transition regions. Moreover, we analyze a general rule regarding the LLT and F-S transition in MGs, along with their composition-dependent peculiarities. This work sheds light on the process of liquid-solid inheritance of different MGs, and deepens the understanding of the liquid dynamics of MGs and their following GFA.

Fragile-to-strong transition and the conversion of structural motifs in Ge-Se glass-forming liquids

Fragile-to-strong (F-S) transition in chalcogenide glass-forming liquids (GFLs) has attracted attention due to its significance in improving the performance of phase-change materials. The present work reports the general characteristics of the F-S transition in chalcogenide GexSe1-x system (0.2<x<0.33). In this composition range, the transition strength parameter f is basically constant and about 2.4. The reduced transition temperature Tf-s/Tg decreases with decreasing the liquid covalency (increasing Ge content). The structural conversion of corner-shared tetrahedra to edge-shared tetrahedra in Ge-Se supercooled liquids has been investigated. This structural conversion controls the liquid dynamics in the low-temperature region near Tg, where the liquid exhibits strong behavior. The rigid constraint is broken and the network becomes floppy in the high-temperature region, which makes the liquid show fragile behavior. These findings are expected to provide a method to tune the Tf-s value of chalcogenide GFLs and a possible structural scenario for the F-S transition in them.

The connection between the fragile-to-strong transition and the liquid-liquid transition in a binary alloy system

Although the liquid-liquid transition (LLT) and the fragile-to-strong (F-S) transition occur in many of glass-forming liquids, the fundamental question about whether and how the two transitions are connected with one another remains unanswered. Here we report an inverse correlation between the F-S transition and the liquid-liquid transition by comparing the glass forming ability (GFA) among various CuZr metallic systems. Based on both molecular dynamic simulations and experiments, the inverse correlation is associated with the difference in the cluster rearrangements between supercooled and equilibrium liquids. We have found and clarified why the LLT is not pronounced for some of alloy systems. Finally we have established a general law for the structural inheritance of equilibrium MGFLs to glass state. The findings in this work are useful for designing the metallic systems with high GFA.

Tailorable fragile-to-strong kinetics features of metal oxides nanocomposite phase-change antimony films

A fragile-to-strong (F-S) kinetics feature is desirable in phase-change supercooled liquids, for decoupling the contradictory relation between good thermal stability nearby glass transition temperature and fast crystallization speed around melting temperature. We designed three metal oxides (MOs), i.e., the fragile TiO2, the moderate ZnO, and the strong GeO2, doping into a very fragile Sb matrix, which is an ideal elementary phase-change material (PCM) for overcoming the composition segregation in fatigued device, to tailor the F-S transition behavior in their supercooled liquids. Depending on the crystallization kinetics analyses of three representative films, which all exhibit the similar thermal stability with crystallization temperature of 200 ± 6 ºC, crystallization activation energy of 2.83 ± 0.09 eV, and the temperature for ten years data retention of 101 ± 7 ºC, we found no F-S behavior in the Sb62.1(TiO2)37.9 film, but weak and strong F-S behavior in Sb82.7(ZnO)17.3 and Sb73.6(GeO2)26.4 film, respectively. It shows that, the Sb based nanocomposite films with different MOs that have various fragilities can bring tailorable F-S kinetics features. Nevertheless, although the metal elementaries of Ti, Zn, Ge, have been confirmed could not bond with the Sb atoms, the Sb2O3 phase are detected more or less in Sb62.1(TiO2)37.9 and Sb82.7(ZnO)17.3 but not found in Sb73.6(GeO2)26.4 film. It is thus believed the formation of Sb2O3 would impede the F-S behavior in the supercooled liquids. The Sb73.6(GeO2)26.4 film that has large F-S transition magnitude of 2.3 and high F-S transition temperature of 536 K, is suggested to be a candidate for potential phase-change memory application. Such distinct F-S behavior in nano-size confined Sb73.6(GeO2)26.4 matrix, which consists of phase-changeable Sb and non-phase-changeable GeO2, stems from the competition between short-range ordering cluster that with abundant Peierls-like distortions in fragile Sb phase and medium-range ordering cluster that with energetical favorable networks in strong GeO2 phase.

Dynamic heterogeneity, cooperative motion, and Johari-Goldstein [Formula: see text]-relaxation in a metallic glass-forming material exhibiting a fragile-to-strong transition.

We investigate the Johari-Goldstein (JG) [Formula: see text]-relaxation process in a model metallic glass-forming (GF) material ([Formula: see text]), previously studied extensively by both frequency-dependent mechanical measurements and simulation studies devoted to equilibrium properties, by molecular dynamics simulations based on validated and optimized interatomic potentials with the primary aim of better understanding the nature of this universal relaxation process from a dynamic heterogeneity (DH) perspective. The present relatively low temperature and long-time simulations reveal a direct correspondence between the JG [Formula: see text]-relaxation time [Formula: see text] and the lifetime of the mobile particle clusters [Formula: see text], defined as in previous DH studies, a relationship dual to the corresponding previously observed relationship between the [Formula: see text]-relaxation time [Formula: see text] and the lifetime of immobile particle clusters [Formula: see text]. Moreover, we find that the average diffusion coefficient D nearly coincides with [Formula: see text] of the smaller atomic species (Al) and that the 'hopping time' associated with D coincides with [Formula: see text] to within numerical uncertainty, both trends being in accord with experimental studies. This indicates that the JG [Formula: see text]-relaxation is dominated by the smaller atomic species and the observation of a direct relation between this relaxation process and rate of molecular diffusion in GF materials at low temperatures where the JG [Formula: see text]-relaxation becomes the prevalent mode of structural relaxation. As an unanticipated aspect of our study, we find that [Formula: see text] exhibits fragile-to-strong (FS) glass formation, as found in many other metallic GF liquids, but this fact does not greatly alter the geometrical nature of DH in this material and the relation of DH to dynamical properties. On the other hand, the temperature dependence of the DH and dynamical properties, such as the structural relaxation time, can be significantly altered from 'ordinary' GF liquids.

Fragile-to-strong transitions in glass forming liquids

Since they were first reported almost two decades ago, fragile-to-strong (FTS) transitions have been observed in all categories of glass-forming systems including metallic, covalent, ionic and molecular liquids. In these systems, a transition from Arrhenius to non-Arrhenius viscosity behavior is observed in conjunction with anomalies in multiple thermodynamic variables including the heat capacity, the thermal expansion coefficient and the isothermal compressibility. A review of experimental evidences supporting the existence of FTS transitions is presented. In particular FTS transitions are found to be concomitant with a peak in heat-capacity as well as density extrema associated with a negative expansion coefficient in the region of the transition. Moreover, spectroscopic analyses also show distinct structural changes across these liquid-liquid transitions. Reports of FTS transitions in each category of liquid are reviewed.

Fragile-to-strong transitions in glass forming liquids

Since they were first reported almost two decades ago, fragile-to-strong (FTS) transitions have been observed in all categories of glass-forming systems including metallic, covalent, ionic and molecular liquids. In these systems, a transition from Arrhenius to non-Arrhenius viscosity behavior is observed in conjunction with anomalies in multiple thermodynamic variables including the heat capacity, the thermal expansion coefficient and the isothermal compressibility. A review of experimental evidences supporting the existence of FTS transitions is presented. In particular FTS transitions are found to be concomitant with a peak in heat-capacity as well as density extrema associated with a negative expansion coefficient in the region of the transition. Moreover, spectroscopic analyses also show distinct structural changes across these liquid-liquid transitions. Reports of FTS transitions in each category of liquid are reviewed.

Intrinsic correlation of the plasticity with liquid behavior of bulk metallic glass forming alloys

Nowadays, plasticizing has become a critical issue for the engineering application of bulk metallic glasses (BMGs). What is the origin of plastic flow and how to evaluate the plasticity of BMGs with a unified standard are still open questions. Here we report a universal fragility criterion to scale the plasticity of BMGs from the equilibrium liquids and supercooled liquids. Based on our experimentally measured and previously reported viscosities at superheated and supercooled region for 51 glasses, the plasticity (ε) of BMGs has been found to positively correlate to the supercooling liquid fragility (m) with the equation of ε = 92exp[− 73/(m−15)], where ε is the plastic strain and m the fragility near glass transition temperature, but negatively correlate to the fragile-to-strong (F-S) transition tendency characterized by F-S transition factor and temperature. The intrinsic mechanism of the plasticity can be well interpreted in the frame of structural relaxation theory. This work provides a new insight into the microscopic essence of the plasticity of glassy solids and a universal approach to scale the fluidity of metallic glasses.

Crystallization Kinetics of GeSbTe Phase-Change Nanoparticles Resolved by Ultrafast Calorimetry.

Although nanostructured phase-change materials (PCMs) are considered as the building blocks of next-generation phase-change memory and other emerging optoelectronic applications, the kinetics of the crystallization, the central property in switching, remains ambiguous in the high-temperature regime. Therefore, we present here an innovative exploration of the crystallization kinetics of Ge2Sb2Te5 (GST) nanoparticles (NPs) exploiting differential scanning calorimetry with ultrafast heating up to 40 000 K s–1. Our results demonstrate that the non-Arrhenius thermal dependence of viscosity at high temperature becomes an Arrhenius-like behavior when the glass transition is approached, indicating a fragile-to-strong (FS) crossover in the as-deposited amorphous GST NPs. The overall crystal growth rate of the GST NPs is unraveled as well. This unique feature of the FS crossover is favorable for memory applications as it is correlated to improved data retention. Furthermore, we show that methane incorporation during NP production enhances the stability of the amorphous NP phase (and thereby data retention), while a comparable maximum crystal growth rate is still observed. These results offer deep insight into the crystallization kinetics of nanostructured GST, paving the way for designing nonvolatile memories with PCM dimensions smaller than 20 nm.

Fragile-to-strong transition in metallic glass-forming liquids

It has been observed that many glass-forming liquids are transformed from fragile to strong liquids in a supercooled region upon cooling. This is the so-called fragile-to-strong (F-S) transition. Since its discovery in water, the F-S transition, as a frontier problem, as well as a hot issue, in condensed matter physics and material science, has aroused the considerable interest of researchers. It has been generally accepted that the F-S transition might be a universal dynamic behavior of metallic glass-forming liquid (MGFL). Studying the F-S transition is important not only for better understanding the nature of glass transition, uncovering the microstructural inheritance during the liquid-solid transformation, clarifying the structural competition during crystallization, improving the stability of MGs, but also for promoting the standardization during the production and treatment technology of MGs. In this paper, the general and special features of the F-S transition for bulk and marginal MGFLs are studied and described in terms of a physical model. A characteristic parameter f is introduced to quantify the F-S transition. With two relaxation regimes, on the basis of Mauro-Yuanzheng-Ellison-Gupta-Allan model, we propose a generalized viscosity model for capturing the liquids with the F-S transition. Using this model, we calculate the F-S transition temperature for metallic glass. From the calculation results, the F-S transition might occur around (1.36±0.03) Tg. By using the hyperquenching annealing-calorimetric approach, we find that the anomalous crystallization behavior occurs in both LaAlNi and CuZrAl glass ribbons. This phenomenon implies the existence of a thermodynamic F-S transition, which could be used as an alternative method of detecting the F-S transition in MGFLs. To date, the origin of the F-S transition is far from understanding. We find that the F-S transition in CuZr(Al) GFLs is attributed to the competition among the MRO clusters composed of different locally ordering configurations. By comparing the parameter f with the parameter r that characterizes the competition between the α and the slow β relaxations in 19 MGFLs, we find that the slow β relaxation plays a dominant role in the F-S transition and the extent of the F-S transition is mainly determined by the degree of the comparability in structure units between the α and the slow β relaxations. The existence of the liquid-liquid phase transition might also be the root of the F-S transition. The tendency of investigation of the F-S transition is also evaluated.

Structural evolution during fragile-to-strong transition in CuZr(Al) glass-forming liquids.

In the present work, we show experimental evidence for the dynamic fragile-to-strong (F-S) transition in a series of CuZr(Al) glass-forming liquids (GFLs). A detailed analysis of the dynamics of 98 glass-forming liquids indicates that the F-S transition occurs around Tf-s ≈ 1.36 Tg. Using the hyperquenching-annealing-x-ray scattering approach, we have observed a three-stage evolution pattern of medium-range ordering (MRO) structures during the F-S transition, indicating a dramatic change of the MRO clusters around Tf-s upon cooling. The F-S transition in CuZr(Al) GFLs is attributed to the competition among the MRO clusters composed of different locally ordering configurations. A phenomenological scenario has been proposed to explain the structural evolution from the fragile to the strong phase in the CuZr(Al) GFLs.

Anomalous crystallization as a signature of the fragile-to-strong transition in metallic glass-forming liquids.

We study the fragile-to-strong (F-S) transition of metallic glass-forming liquids (MGFLs) by measuring the thermal response during annealing and dynamic heating of La55Al25Ni5Cu15 glass ribbons fabricated at different cooling rates. We find that the glasses fabricated in the intermediate regime of cooling rates (15-25 m/s) exhibit an anomalous crystallization behavior upon reheating as compared to the glasses formed at other cooling rates. This anomalous crystallization behavior implies the existence of a thermodynamic F-S transition, could be used as an alternative method for detecting the F-S transition in MGFLs, and sheds light on the structure origin of the F-S transition. This work also contributes to obtaining a general thermodynamic picture of the F-S transition in supercooled liquids.

A Direct Link between the Fragile-to-Strong Transition and Relaxation in Supercooled Liquids.

It is known that both the fragile-to-strong (F-S) transition and relaxation processes occur in numerous supercooled liquids upon cooling toward the glass transition temperature. The key question is whether and how these two dynamic processes are correlated. Here, we show a direct link between the two processes for both metallic glass-forming liquids (MGFLs) with different fragilities and also for nonmetallic glass-forming liquids. By comparing the F-S transition extent parameter f with the parameter r that characterizes the competition between the α and the slow β relaxations, we have discovered a negative exponential connection between the two parameters of supercooled liquids. The finding indicates that the slow β relaxation plays a dominant role in the F-S transition. This work provides new insight into the microscopic mechanism of the F-S transition and creates a strong basis for predicting whether and to what extent the F-S transition occurs in supercooled liquids.

Neutron spin echo measurements of monolayer and capillary condensed water in MCM-41 at low temperatures

Neutron spin echo measurements of monolayer and capillary condensed heavy water (D2O) confined in MCM-41 C10 (pore diameter 2.10 nm) were performed in a temperature range of 190–298 K. The intermediate scattering functions were analyzed by the Kohlrausch–Williams–Watts stretched exponential function. The relaxation times of confined D2O in the capillary condensed state follow remarkably well the Vogel–Fulcher–Tammann equation between 298 and 220 K, whereas below 220 K they show an Arrhenius type behavior. That is, the fragile-to-strong (FTS) dynamic crossover occurs, which has never been seen in experiments on bulk water. On the other hand, for monolayer D2O, the FTS dynamic crossover was not observed in the temperature range measured. The FTS dynamic crossover observed in capillary condensed water would take place in the central region of the pore, not near the pore surface. Because the tetrahedral-like water structure in the central region of the pore is more preserved than that near the pore surface, the FTS dynamic crossover would be concerned with the tetrahedral-like water structure.

Reply to Elmatad: Supercooled viscous liquids display a fragile-to-strong dynamic crossover

Theory predicts a fragile-to-strong (FS) dynamic crossover temperature Tx in supercooled liquids but, contrary to what is reported in ref. 1, Tx must be >Tg (2), where Tg is the glass transition temperature. Ref. 4 of ref. 1 hypothesizes that a parabolic form is valid in a range To > T > Tx, where To is defined as an onset temperature that marks the crossover from normal liquid behavior to supercooled liquid behavior. A second paper by the same authors (ref. 5 of ref. 1) proposes the range of the hypothesized parabolic behavior can be extended to cover T To, changes of three to four orders of magnitude take place in transport parameter values. Moreover, glass transition theories such as mode coupling theory (2) consider these data to be extremely relevant.

Fragile-to-strong transition in metallic glass-forming liquids

Two of the Earth's most abundant substances, water and silica, exhibit some of the most unusual properties in nature. Among these is an anomalous scaling of liquid dynamics, which appear non-Arrhenius (or "fragile") at high temperatures yet Arrhenius (or "strong") at low temperatures. Here we show that this fragile-to-strong (F-S) transition is not limited to a few liquids such as water and silica, but is possibly a general behavior of metallic glass-forming liquids. We also propose a general model for the viscosity of F-S liquids that captures the scaling of dynamics across both the fragile and strong regimes.

Quasielastic and inelastic neutron scattering investigation of fragile-to-strong crossover indeeply supercooled water confined in nanoporous silica matrices

We investigated, using quasi-elastic and inelastic neutron scattering, the slowsingle-particle dynamics of water confined in laboratory synthesized nanoporous silicamatrices, MCM-41-S, with pore diameters ranging from 10 to 18 Å. Inside the poresof these matrices, the freezing process of water is strongly inhibited down to160 K. We analysed the quasi-elastic part of the neutron scattering spectra with arelaxing-cage model and determined the temperature and pressure dependence of theQ-dependent translational relaxation time and its stretch exponentβ for the time dependence of the self-intermediate scattering function. The calculatedQ-independent average translational relaxation time shows a fragile-to-strong (FS) dynamiccrossover for pressures lower than 1600 bar. Above this pressure, it is no longerpossible to discern the characteristic feature of the FS crossover. Identificationof this end point with the predicted second low-temperature critical point ofwater is discussed. A subsequent inelastic neutron scattering investigation of thelibrational band of water indicates that this FS dynamic crossover is associated with astructural change of the hydrogen-bond cage surrounding a typical water moleculefrom a denser liquid-like configuration to a less-dense ice-like open structure.

Pressure Dependence of Fragile-to-Strong Transition and a Possible Second Critical Point in Supercooled Confined Water

By confining water in nanopores of silica glass, we can bypass the crystallization and study the pressure effect on the dynamical behavior in deeply supercooled state using neutron scattering. We observe a clear evidence of a cusplike fragile-to-strong (FS) dynamic transition. Here we show that the transition temperature decreases steadily with an increasing pressure, until it intersects the homogenous nucleation temperature line of bulk water at a pressure of 1600 bar. Above this pressure, it is no longer possible to discern the characteristic feature of the FS transition. Identification of this end point with the possible second critical point is discussed.