Glass State Research Articles

Tailoring carbon nanotubes quickly into graphene nanoribbons along axis-direction via dynamic magnetic flux template

So far, the method of top-down preparing graphene nanoribbons by etching of carbon nanotubes (CNTs) mainly relies on the catalytic reaction of Fe, Co, and Ni nanoparticles. However, etching cannot be guaranteed along the CNT axis only. In this study, Ti3AlC2 is decomposed into liquid aluminum in the dynamic magnetic flux template to catalyze the growth of multiwalled carbon nanotubes (MWCNTs). Successively, the obtained MWCNTs are etched in-situ by rutile TiO2 particles to generate multilayered graphene nanoribbons (MLGNRs). Thus-obtained nanoribbons will create zigzag edges full of short-range order segment, demonstrating a spin glass state. This work has paved a new way for a top-down approach to create MLGNRs by tailoring MWCNTs along axis direction only using dynamic magnetic flux template.

A method to estimate the temperature at which the physical properties of dried noodles change

A method is proposed to detect the temperature, Tphy, at which dried noodles change their physical state during heating. The method was applied to dried spaghetti and udon (a Japanese noodle made from all-purpose wheat flour), and tested at various moisture contents. For both spaghetti and udon, Tphy almost coincided with the glass transition temperature, Tg, of noodles as determined by differential scanning calorimetry (DSC) when their moisture contents were about 0.15 kg-H2O/kg-d.m. or more. However, at moisture content levels less than this, Tphy was considerably lower than Tg and almost matched the temperature at which the DSC curve began to change stepwise in the first heating for the samples with no pretreatment for eliminating the effect of thermal history. The Tphy corresponded with the temperature at which relaxation due to the secondary molecular ordering occurred in the glass state.

Scaling of the non-phononic spectrum of two-dimensional glasses.

Low-frequency vibrational harmonic modes of glasses are frequently used to rationalize their universal low-temperature properties. One well studied feature is the excess low-frequency density of states over the Debye model prediction. Here, we examine the system size dependence of the density of states for two-dimensional glasses. For systems of fewer than 100 particles, the density of states scales with the system size as if all the modes were plane-wave-like. However, for systems greater than 100 particles, we find a different system-size scaling of the cumulative density of states below the first transverse sound mode frequency, which can be derived from the assumption that these modes are quasi-localized. Moreover, for systems greater than 100 particles, we find that the cumulative density of states scales with the frequency as a power law with the exponent that leads to the exponent β = 3.5 for the density of states. For systems whose sizes were investigated, we do not see a size-dependence of exponent β.

Fabrication of aluminum titanate–glass composites with controlled thermal expansion and improved mechanical strength

Aluminum titanate–glass sintered composites with a controlled thermal expansion coefficient were successfully prepared by the solid-state reaction of Al2O3, TiO2, and soda-lime glass powders. The thermal expansion of the specimens monotonically increased from negative to positive when the glass addition was increased from 0 to 30 wt%, indicating that a zero-thermal-expansion material could be obtained at a glass addition of 5–7 wt%. Chemical reaction between glass and Al2TiO5 was not observed during sintering, and the glassy state of the raw soda-lime glass was maintained. The scanning electron microscopy–energy-dispersive X-ray spectroscopy results indicate that the glassy phase penetrates the grain boundaries of the sintered composites with a glass addition of 5 wt%, thereby increasing the thermal expansion coefficient and apparent density. For the composites with a glass content of >5 wt%, a glassy phase that possibly forms outside the grain boundary could increase the thermal expansion coefficient and decrease the density. The glassy phase at the grain boundary also effectively improved the mechanical bending strength.

Canonical spin glass and cluster glass behavior in the polymorphs of LiFeSnO4

We report a comprehensive and comparative study of structural, static, dynamic, and nonequilibrium magnetic properties on the polymorphs of $\mathrm{LiFeSn}{\mathrm{O}}_{4}$. It exhibits two polymorphs: (i) orthorhombic phase (HT) stabilized at high temperature and (ii) hexagonal phase (LT) obtained at lower synthetic temperature. The HT phase crystallizes in the orthorhombic structure (space group: Pmcn) and exhibits a site disordered, nonfrustrated zig-zag network of ${\mathrm{Fe}}^{3+}$ and ${\mathrm{Sn}}^{4+}$ ions. On the other hand, the LT phase shows a disordered frustrated kagome network of ${\mathrm{Li}}^{1+}, {\mathrm{Fe}}^{3+}$, and ${\mathrm{Sn}}^{4+}$ ions crystallizing in the hexagonal structure (space group: $P{6}_{3}mc$). The low-temperature thermo-magnetic irreversibility and the absence of heat capacity anomaly in both polymorphs indicate the absence of long-range magnetic ordering and a possible glassy state. Zero-field-cooled and field-cooled magnetic memory effect and spin relaxation measurements stipulate the spin glass nature of the polymorphs. Further, spin glass behavior is confirmed by the AC susceptibility measurements. Interestingly, these polymorphs reveal different classes of spin glass states. The site disordered HT phase exhibits a single spin-flip time ${\ensuremath{\tau}}_{0}\ensuremath{\sim}3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}$ sec, indicating a canonical spin glass state. In contrast, LT phase, which is disordered and geometrically frustrated, shows the spin-flip time of ${\ensuremath{\tau}}_{0}\ensuremath{\sim}9\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}$ sec, suggesting a cluster spin glass state. In addition, the exchange bias effect was observed due to magnetic inhomogeneity in both polymorphs.

Effect of cryogenic cycling and above-Tg annealing on the corrosion behavior of Zr-Cu-Ti-Be metallic glass

This work investigates the electrochemical properties of Zr-based Zr35Ti30Cu8.25Be26.75 metallic glass after cryogenic treatment and isothermal annealing above glass transition temperature. Potentiodynamic polarization and electrochemical impedance spectroscopy experiments are used to understand the effect of structural state on the corrosion behavior of Zr-based metallic glass. The metallic glass samples are cycled between liquid nitrogen to room temperature and isothermally held at liquid nitrogen to unravel the effect of cryogenic treatments on the electrochemical properties. The corrosion of cryogenically treated and high temperature annealed samples is compared with the as-cast samples. The results show that holding at liquid nitrogen temperature improves the corrosion resistance of metallic glass compared to cryogenic cycling and the high temperature annealing. These findings are explained based on the changes in structural state of metallic glass.

Crystal growth of CeMn0.85Sb2: Absence of magnetic order of Ce-sublattice

Single crystals of CeMn0.85Sb2 have been successfully synthesized by using the Bi as flux. Analysis of single crystal x-ray diffraction data confirms that CeMn0.85Sb2 crystallizes in the HfCuSi2-type structure with the space group P4/nmm (No. 129). In the case of H||c, CeMn0.85Sb2 displays a robust antiferromagnetic transition at ∼160 K for Mn-sublattice, and there is no sign of magnetic order regarding Ce-sublattice. In the case of H ⊥ c, the Mn-sublattice shows signs of magnetic order at 160 K and 116 K, indicating a possible spin reorientation. There is no sign of magnetic order for the Ce-sublattice either, but, alternating current magnetic susceptibility measurements reveal a spin glass state below 18 K in the case of H ⊥ c. Isothermal magnetization curves measured below magnetic order with H ⊥ c show saturation and even large hysteresis at 2 K, indicating the presence of a ferromagnetic component. In addition, a field-induced spin-flop transition is observed in the case of H ⊥ c, indicating a field-induced spin reorientation of Mn spins. Electrical resistivity measurements indicate a metallic nature for CeMn0.85Sb2 and large anisotropy which is consistent with its quasi-two-dimensional layered structure.

Li(C2N3) as eutectic forming modifier in the melting process of the molecular perovskite [(C3H7)3N(C4H9)]Mn(C2N3)3±

Coordination polymer (CP) glasses have recently emerged as a new glass state. Given the young state of the field, the discovery of concepts that guide the synthesis of CP glasses with targeted thermal and macroscopic properties is at the center of ongoing research. In our work, we draw inspiration from research on inorganic glasses, investigating the impact of Li(C2N3) as a modifier on the thermal properties of the new molecular perovskite [(C3H7)3N(C4H9)]Mn(C2N3)3 (with [C2N3]− = dicyanamide, DCA). We derive the phase diagram and show that Li(C2N3) and [(C3H7)3N(C4H9)]Mn(C2N3)3 form a eutectic mixture, in which the melting temperature is decreased by 30 K. Additionally, for the eutectic mixture at xLiDCA ≈ 0.4, a CP glass forms under slow cooling, opening interesting pathways for scalable synthesis routes of CP glasses. Given the virtually unlimited parameter space of hybrid modifiers, they will play a major role in the future to alter the glass’ properties where the availability of rigorously derived phase diagrams will be important to identify material class overarching trends.

Two states of magnetic frustration in La0.7Sr0.3MnO3 amorphous films with fractal structures: New knowledge about clusters and cluster ensembles

In amorphous La0.7Sr0.3MnO3 films with a fractal structure, two states of magnetic frustration were found, which are the characteristic of cluster spin glass (CSG) and spin glass (SG) states and are associated with the presence of competing, FM and AFM, magnetic interactions, and the geometry of fractal formations. A high density of clusters in them provides effective magnetic interactions of magnetic moments without the participation of free charge carriers. It has been established that the formation of CSG begins with the transition of the central parts of the clusters to the FM state (at T < 98 K) and ends with the formation of the AFM order in the peripheral areas of the clusters, at T < 64 K. Increasing the field to H = 1.2 kOe, which stimulates AFM ordering of peripheral areas, strengthens the state of the cluster glass. A further decrease in temperature (T < 26 ) and an increase in the field (H > 2.5 kOe) causes the transition of peripheral areas from the AFM to the SG state. A phenomenological description of the frustration process is made. The dependences of the order parameter and barrier height on temperature and magnetic field have been studied. The consequences of the CSG ⇒ SG phase transition for the magnetism of the samples and the direct influence of the external field on their magnetic structure are discussed.

Viewing high entropy alloys through glasses: Linkages between solid solution and glass phases in multicomponent alloys

High entropy alloys (HEAs) represent highly promising multicomponent crystals that form concentrated solid solutions (CSSs) and may violate traditional thermodynamic rules of mixing, ultimately leading to excellent physical properties. For a deeper understanding, we investigate seven CSSs, including Co-Cr-Ni-Fe-Mn elements, at experimentally relevant compositions and conditions, through molecular simulations, and we use 1-1 comparisons to corresponding glass state characteristics, attained through rapid cooling protocols. We determine the behavior of various structural features, including the configurational entropy for a set of CSSs in their crystalline and vitreous states numerically. We employ swap Monte Carlo (MC) simulations, in combination with the reversible scaling method, to efficiently compute the configurational entropy (${S}_{\text{conf}}$), and show that the entropic rule of mixing is not always adequate for predicting alloy formation. We study the stability and formability of crystalline solid solutions, as well as glasses, while following the thermodynamics of ${S}_{\text{conf}}$. An apparent entropic similarity between CSSs and corresponding glasses leads us to use a Kauzmann-like ansatz, relating the CSSs at ${S}_{\text{conf}}\ensuremath{\rightarrow}0$ with the emergence of a CSS order-disorder transition, at temperature ${T}_{OD}$. In the context of glasses, a comparison between kinetic and thermodynamic fragilities allows the association of sluggish diffusion onset to a drop in ${S}_{\text{conf}}$ at ${T}_{K}$. Analogously, we classify CSSs as ``strong'' or ``fragile'' in the sense of their ability to migrate across CSS crystal configurations at high temperatures, distinguishing its formability. We argue that the magnitude of ${T}_{OD}$ may be an excellent predictor of CSS single-phase stability, which appears to scale with well-known HEA predictors, in particular we notice that VEC and ${T}_{OD}$ have in relation to the others a significantly large Pearson correlation coefficient, much larger than most other observables (except $\mathrm{\ensuremath{\Delta}}{H}_{\text{mix}}$).

Non-equilibrium view of the amorphous solidification of liquids with competing interactions.

The interplay between short-range attractions and long-range repulsions (SALR) characterizes the so-called liquids with competing interactions, which are known to exhibit a variety of equilibrium and non-equilibrium phases. The theoretical description of the phenomenology associated with glassy or gel states in these systems has to take into account both the presence of thermodynamic instabilities (such as those defining the spinodal line and the so called λ line) and the limited capability to describe genuine non-equilibrium processes from first principles. Here, we report the first application of the non-equilibrium self-consistent generalized Langevin equation theory to the description of the dynamical arrest processes that occur in SALR systems after being instantaneously quenched into a state point in the regions of thermodynamic instability. The physical scenario predicted by this theory reveals an amazing interplay between the thermodynamically driven instabilities, favoring equilibrium macro- and micro-phase separation, and the kinetic arrest mechanisms, favoring non-equilibrium amorphous solidification of the liquid into an unexpected variety of glass and gel states.

Searching for spin glass ground states through deep reinforcement learning

Spin glasses are disordered magnets with random interactions that are, generally, in conflict with each other. Finding the ground states of spin glasses is not only essential for understanding the nature of disordered magnets and many other physical systems, but also useful to solve a broad array of hard combinatorial optimization problems across multiple disciplines. Despite decades-long efforts, an algorithm with both high accuracy and high efficiency is still lacking. Here we introduce DIRAC – a deep reinforcement learning framework, which can be trained purely on small-scale spin glass instances and then applied to arbitrarily large ones. DIRAC displays better scalability than other methods and can be leveraged to enhance any thermal annealing method. Extensive calculations on 2D, 3D and 4D Edwards-Anderson spin glass instances demonstrate the superior performance of DIRAC over existing methods. The presented framework will help us better understand the nature of the low-temperature spin-glass phase, which is a fundamental challenge in statistical physics. Moreover, the gauge transformation technique adopted in DIRAC builds a deep connection between physics and artificial intelligence. In particular, this opens up a promising avenue for reinforcement learning models to explore in the enormous configuration space, which would be extremely helpful to solve many other hard combinatorial optimization problems.

Searching for the ideal glass transition: Going to yotta seconds and beyond

Here we report results for the dynamics of a 50-million-year-old (geologically) aged Fushun amber that had a fictive temperature Tfapproximately 193 K below its glass transition temperatureTg in the thermally rejuvenated state. The density of this ultra-stable amber was found to be 14% greater than the post-rejuvenation value. Length change dilatometry was used to map the Tf by performing de-aging experiments and equilibrium state dynamics were obtained by making measurements at T=Tf. Time-Temperature Superposition was applied to the frequency dependent storage and loss modulus measurements both along the equilibrium line and in upper-bound conditions where T>Tf. We find that the relaxation times cover >1027s (1 ronna second), i.e., thousands of yotta seconds but do not follow the “expected” Vogel-Fulcher-Tammann (VFT) type of super-Arrhenius type of temperature dependence. Rather the deep glassy state equilibrium dynamics show no evidence of divergence at a finite temperature for temperatures that would be expected to be far below the ideal glass temperature Tg,ideal. In addition, at constant fictive temperature, we find that the relaxation times vary very strongly with specific volume v whereas, in isothermal conditions, the relaxation times are only weakly dependent on v. These results evidence that the deep glass state behavior presents a challenge to current ideas about glasses and the glass transition.

Non-monotonic influence of cryogenic thermal cycling on rejuvenation and impact toughness of Ti-based bulk metallic glass composites

Cryogenic thermal cycling (CTC) can alter the energy states of bulk metallic glasses (BMGs) and their composites (BMGCs), but the fundamental mechanisms of CTC and their effects on mechanical properties are largely remain elusive. Herein, the effects of CTC on structural evolution and impact toughness, aK, of Ti-based BMGCs containing β-Ti dendrites are investigated. It is found that either rejuvenation or relaxation alternately dominates the structural evolution of the glass matrix, causing a non-monotonic rejuvenation. At 298 K, a more rejuvenated state causes a synergistic toughening by both of the glass matrix and dendrites, and the aK variation trend of BMGCs is the same as the non-monotonic rejuvenation. However, at 77 K, the aK variation trend of BMGCs is just opposite as the non-monotonic rejuvenation of the glass matrix. The rejuvenation/relaxation during CTC are correlated with the impact toughness, which provides a basis for improving toughness of BMGCs by CTC.

Large exchange bias in Mn-Ni-Sn Heusler alloys: Role of cluster spin glass state

We report a combined experimental and theoretical study of the exchange bias (EB), structural and magnetic properties of manganese-rich ${\mathrm{Mn}}_{50}{\mathrm{Ni}}_{41.5+x}{\mathrm{Sn}}_{8.5\ensuremath{-}x}$ $(x\phantom{\rule{4pt}{0ex}}=0, 0.75, \text{and} 1)$ Heusler alloys. All these alloys crystallize in a tetragonal structure at room temperature. Ab initio simulation using density functional theory (DFT) on off-stoichiometric ${\mathrm{Mn}}_{50}{\mathrm{Ni}}_{42.1875}{\mathrm{Sn}}_{7.8125}$ alloy (very close to the actual composition) predicts the tetragonal structure with the ferrimagnetic arrangement as the ground state, in good agreement with the experimental results. These alloys are found to exhibit a large exchange bias at low temperatures, with a maximum EB field of 7.1 kOe at 2 K for $x\phantom{\rule{4pt}{0ex}}=1$, which is significantly larger than that reported for any Mn-Ni--based Heusler systems. Frequency dependence of spin freezing temperature obeying the scaling law confirms the presence of a cluster spin glass (CSG)--like state in these alloys. The latter is also confirmed from the memory and aging effect studies in zero-field cooling and field-cooled protocols for these alloys. The large EB is attributed to the strong exchange coupling between the CSG clusters embedded in an otherwise ferrimagnetic matrix. The exchange mechanism behind the large EB effect is discussed in the light of varying bond lengths between different magnetic pairs, and hence the magnetic coupling, due to the large tetragonal distortion. The present experimental findings are found to be in good agreement with the DFT results.

Honeycomb oxide heterostructure as a candidate host for a Kitaev quantum spin liquid

Kitaev quantum spin liquid, massively quantum entangled states, is so scarce in nature that searching for new candidate systems remains a great challenge. Honeycomb heterostructure could be a promising route to realize and utilize such an exotic quantum phase by providing additional controllability of Hamiltonian and device compatibility, respectively. Here, we provide epitaxial honeycomb oxide thin film Na3Co2SbO6, a candidate of Kitaev quantum spin liquid proposed recently. We found a spin glass and antiferromagnetic ground states depending on Na stoichiometry, signifying not only the importance of Na vacancy control but also strong frustration in Na3Co2SbO6. Despite its classical ground state, the field-dependent magnetic susceptibility shows remarkable scaling collapse with a single critical exponent, which can be interpreted as evidence of quantum criticality. Its electronic ground state and derived spin Hamiltonian from spectroscopies are consistent with the predicted Kitaev model. Our work provides a unique route to the realization and utilization of Kitaev quantum spin liquid.

Ergodicity breaking of an inorganic glass aging near Tg probed by elasticity relaxation

We performed a series of aging experiments with an inorganic glass (${\mathrm{As}}_{2}{\mathrm{Se}}_{3}$) at a temperature ${T}_{2}$ near the glass transition point ${T}_{g}$ by first relaxing it at ${T}_{1}$. The relaxations of Young's modulus were monitored, which were (almost if not ideally) exponential with ${T}_{1}$-dependent relaxation time \ensuremath{\tau}, corroborating the Kovacs' paradox in an inorganic glass. Associated with the divergence of \ensuremath{\tau}, the quasiequilibrated Young's modulus ${E}_{\ensuremath{\infty}}$ does not converge either. An elastic model of relaxation time and a Mori-Tanaka analysis of ${E}_{\ensuremath{\infty}}$ lead to a similar estimate of the persistent memory of the history, illuminating ergodicity breaking within the accessible experimental time, as described in the Gardner transition theory. Experiments with different ${T}_{2}$ exhibit a critical temperature ${T}_{p}\ensuremath{\sim}{T}_{g}$, i.e., when ${T}_{2}>{T}_{p}$, both \ensuremath{\tau} and ${E}_{\ensuremath{\infty}}$ converge. The results unveil a long-expected phenomenon that structural glass transition could be a zero-to-nonzero transition, manifested by a nonvanishing structural memory in aging when the temperature is below ${T}_{p}$ in the glass transition range. This demonstrates the existence of the ergodicity breaking deep in the glass state and ${T}_{p}$ could be the Gardner transition point of the structural glass.

Multiple Magnetic Phases and Anomalous Hall Effect in Sb1.9Fe0.1Te2.85S0.15 Topological Insulators

Due to fundamental and technological concerns, investigating materials with topological magnetic structures has always been a focus of significant research. We explored Sb1.9Fe0.1Te2.85S0.15 where a unique combination of disordered glassy phases, competitive FM–AFM interactions, and nontrivial surface state coexisted at the same time. We have discussed the impact of those complicated magnetic phases upon the observed AHE in Sb1.9Fe0.1Te2.85S0.15 with magneto-transport studies. The AC susceptibility results demonstrate a shift in the freezing temperature with excitation frequency, the comprehensive analysis verifies the slower dynamics, and a nonzero Vogel–Fulcher temperature T0 suggests cluster spin glass. This, together with an intermediate value of the Mydosh parameter, provides an evidence for the formation of a cluster spin glass state in the present system. Topological frustrated magnets, which can host both magnetic frustrations and Dirac quasi-particles, are highly sought after class of compounds. Furthermore, as seen by the de Haas–van Alphen (dHvA) oscillation study, the fermiology deviates with doping and produces multiple Fermi pockets, revealing a rich complexity in the underlying electronic structure.

Crystal nucleation in a glass during relaxation well below Tg.

Until quite recently, in almost all papers on crystal nucleation in glass-forming substances, it was assumed that nucleation proceeds in a completely relaxed supercooled liquid and, hence, at constant values of the critical parameters determining the nucleation rate for any given set of temperature, pressure, and composition. Here, we analyze the validity of this hypothesis for a model system by studying nucleation in a lithium silicate glass treated for very long times (up to 250 days) in deeply supercooled states, reaching 60K below the laboratory glass transition temperature, Tg. At all temperatures in the considered range, T < Tg, we observed an enormous difference between the experimental number of nucleated crystals, N(t), and its theoretically expected value computed by assuming the metastable state of the relaxing glass has been reached. Analyzing the origin of this discrepancy, we confirmed that the key parameters determining the nucleation rates change with time as a result of the glass relaxation process. Finally, we demonstrate that, for temperatures below 683K, this particular glass almost fully crystallizes prior to reaching the ultimate steady-state nucleation regime (e.g., at 663K, it would take 176 years for the glass to reach 99% crystallization, while 2600 years would be needed for complete relaxation). This comprehensive study proves that structural relaxation strongly affects crystal nucleation in deeply supercooled states at temperatures well below Tg; hence, this phenomenon has to be accounted for in any crystal nucleation model.

Isothermal enthalpy relaxation of amorphous polystyrene studied using temperature-modulated fast scanning calorimetry

The kinetics of enthalpy relaxation of atactic polystyrene after temperature jump-down and jump-up in the glass state is studied using temperature-modulated fast scanning calorimetry (T-M FSC). During the isothermal relaxation, the dynamic heat capacity obtained by T-M FSC underwent a systematic change suggesting a shift of relaxation time. The relaxation time in the nonequilibrium glass state is dependent on the sample's actual temperature T and the nonequilibrium structure that has been indexed by a fictive temperature Tf. The changes in the magnitude and phase angle of the dynamic heat capacity on relaxation prove the influence of the nonequilibrium structure. The influence is indexed by an effective temperature Teff, which is derived from the obtained dynamic heat capacity compared with its temperature dispersion in the liquid state. Teff also corresponds to the mean temperature of the actual and fictive temperatures and can be expressed by Teff≅xT+(1−x)Tf with the nonlinearity parameter x of the Tool–Narayanaswamy–Moynihan model that partitions the activation factor of relaxation into the contributions of T and Tf. Evaluation of Tf and Teff will provide valuable insights into the relaxation time in glass state, which plays an essential role in the glass transition behaviors of amorphous materials.