Glassy Systems Research Articles

Fragmented perspective of self-organized criticality and disorder in log gravity

We use a statistical model to discuss nonequilibrium fragmentation phenomena taking place in the stochastic dynamics of the log sector in log gravity. From the canonical Gibbs model, a combinatorial analysis reveals an important aspect of the n-particle evolution previously shown to generate a collection of random partitions according to the Ewens distribution realized in a disconnected double Hurwitz number in genus zero. By treating each possible partition as a member of an ensemble of fragmentations, and ensemble averaging over all partitions with the Hurwitz number as a special case of the Gibbs distribution, a resulting distribution of cluster sizes appears to fall as a power of the size of the cluster. Dynamical systems that exhibit a distribution of sizes giving rise to a scale-invariant power-law behavior at a critical point possess an important property called self-organized criticality. As a corollary, the log sector of log gravity is a self-organized critical system at the critical point μl = 1. A similarity between self-organized critical systems, spin glass models and the dynamics of the log sector which exhibits aging behavior reminiscent of glassy systems is pointed out by means of the Pòlya distribution, also known to classify various models of (randomly fragmented) disordered systems, and by presenting the cluster distribution in the log sector of log gravity as a distinguished member of this probability distribution. We bring arguments from a probabilistic perspective to discuss the disorder in log gravity, largely anticipated through the conjectured AdS3/LCFT2 correspondence.

Short and long range ordering on dielectric relaxation of AgI doped glass-ceramic

The dielectric relaxation process of an amorphous glassy system, AgI - CdO -V2O5 -P2O5 - ZnO has been reported here. Electric modulus formalism has been carried out to explore the dielectric behavior of the as-prepared samples and the experimental results have been analyzed in the light of some theoretical models. Study of the nature of peak separation between imaginary components of electric modulus and the complex impedance plots reveals that the present system with lower AgI content should have a tendency to exhibit long range order for the relaxation of charge carriers. On the other hand, the present system with higher AgI content exhibits a relaxation process, dominated by short range order of charge carriers. This relaxation process is found to be Debye type for AgI doping up to x = 0.20 and it becomes non-Debye type beyond that composition range.

Preparation and Electrothermal Transport Behavior of Sn8[(Ga2Te3)34(SnTe)66]92 Bulk Glass.

High-conductivity tellurium-based glasses were anticipated to be the attractive candidates in chalcogenide glass systems on account of their distinctive characteristics and extensive application prospects. In this paper, the high-density (>96%) Sn8[(Ga2Te3)34(SnTe)66]92 bulk glass with the density of 5.5917 g/cm3 was successfully prepared by spark plasma sintering (SPS) technology at 460 K, using a 5 min dwell time and 450 MPa pressure. The room-temperature thermal conductivity of Sn8 bulk materials significantly decreased from 1.476 W m-1∙K-1 in the crystalline sample to 0.179 W m-1∙K-1 in the glass, and the Seebeck coefficient obviously increased from 35 μV∙K-1 in to 286 μV∙K-1, indicating that the glass transition of tellurium-based semiconductors could optimize the thermal conductivity and Seebeck coefficient of the materials. Compared to the conventional tellurium-based glassy systems, the fabricated Sn8 bulk glass presented a high room-temperature conductivity (σ = 6.2 S∙m-1) and a large glass transition temperature (Tg = 488 K), which was expected to be a promising thermoelectric material.

Utilizing bypass cement dust in the production of radiation shielding bismuth borate glass

Using the melting-quench technique, a new method for removing bypass cement dust (BCD) was developed in this study using an active environmental glassy system with the chemical formula (65–x)B2O3–5Li2O–5CdO–25BCD–xBi2O3, where x varied from 0 to 30 mol%. A glass density of 3.137 g/cm³ is attained without bismuth, while a density of 5.345 g/cm³ is obtained with 30 mol% Bi2O3. The unit peaks BO3 and BO4 in the FTIR spectra signify the presence of the BLCDBi-series structure. Elevated Bi2O3 concentrations augment BO4 units. Defects influence the optical absorbance of glass within the wavelength range of 190–1000 nm. These defects in the glass network are created by silicon electrons, silicon hole centers, and BCD as well as Bi3+ or Bi6+ after the addition of bismuth oxide to the glassy system. Eg values were found to decrease as Bi2O3 concentration increased, whereas EU and n values exhibited the opposite behavior. A gamma spectroscopy system and the Phy-X/PSD software are used to calculate the linear attenuation coefficient (LAC), mass attenuation coefficient (MAC), half-value layer (HVL), tenth-value layer (TVL), effective atomic number (Zeff), and effective electron density (Neff) of samples. In addition, the Phy-X/PSD software demonstrated good agreement between experimental and theoretical interpretations. Overall, the results showed that the BLCDBi-30 sample is suitable for use in radiation protection.

Characterizing Rotational Dynamics and Heterogeneity via Single-Molecule Intensity Measurements.

Dynamic heterogeneity in glassy systems has typically been characterized at the single-molecule level by extracting rotational relaxation time scales from linear dichroism (LD) collected via two orthogonally polarized channels. However, in such measurements, localization precision is diminished due to photons lost relative to collection in a single detection channel. This poses challenges in characterizing rotational and translational dynamics simultaneously, as translational measurements require high localization precision. In this paper, we present a method for extracting rotational dynamics of glassy systems at the single-molecule level from intensity fluctuations of fluorescent probe molecules in a wide-field configuration without the use of a polarizing optical component. Through numerical analysis, we show that LD and intensity measurements probing rotational dynamics report similar, approximately second-order rotational correlation decays even at low signal to noise. Thus, within the assumptions of small, isotropic rotations, LD and intensity autocorrelation analysis should provide identical information on the time scale and heterogeneity of rotational dynamics. We then present experimental results that validate this numerical result, with direct comparison of LD and intensity-based approaches across probe molecules in both polymeric and small-molecule glass formers as well as across optical configurations. Our results demonstrate moderate correlation on a per-probe basis between rotational time scales obtained from both approaches, with deviations consistent with those expected in a dynamically heterogeneous system. We envision that this easily accessible strategy will be of use across disciplines for characterizing single-molecule rotational dynamics in limited signal situations and/or when high-precision localization is required.

Monte Carlo simulations of glass-forming liquids beyond Metropolis.

Monte Carlo simulations are widely employed to measure the physical properties of glass-forming liquids in thermal equilibrium. Combined with local Monte Carlo moves, the Metropolis algorithm can also be used to simulate the relaxation dynamics, thus offering an efficient alternative to molecular dynamics. Monte Carlo simulations are, however, more versatile because carefully designed Monte Carlo algorithms can more efficiently sample the rugged free energy landscape characteristic of glassy systems. After a brief overview of Monte Carlo studies of glass-formers, we define and implement a series of Monte Carlo algorithms in a three-dimensional model of polydisperse hard spheres. We show that the standard local Metropolis algorithm is the slowest and that implementing collective moves or breaking detailed balance enhances the efficiency of the Monte Carlo sampling. We use time correlation functions to provide a microscopic interpretation of these observations. Seventy years after its invention, the Monte Carlo method remains the most efficient and versatile tool to compute low-temperature properties in supercooled liquids.

Memory and rejuvenation in glassy systems

Memory and rejuvenation in glassy systems

Influence of La3+ ions on the structural, elastic, optical, and radiation shielding properties of Cr2O3-Doped heavy metal glasses

This study investigates the effect of La³⁺ rare earth ions on the structural, elastic, optical, and radiation shielding features of heavy metal borate glass (B₂O₃-PbO) doped with Cr₂O₃. Density measurements and FT-IR spectra analysis revealed the role of La3+ ions as a network modifier, where successive additions of La2O3 content led to a gradual increase in the density and an increase in the non-bridging oxygen content resulting from the structural transformation between the BO4 and BO3 units. The significant improvement in the elastic modulus and microhardness factor moduli was confirmed by calculating the change in ultrasonic velocities through the glassy system. The structural modifications induced by La³⁺ ions narrowed the band gap and increased the Urbach energy, indicating higher disorder within the glass network. The linear refractive indices increased due to increased optical basicity and electronic polarization. Optical absorption results showed that Cr⁶⁺/Cr³⁺ ions occupy octahedral/tetrahedral sites, with the tendency for Cr³⁺ cations to occupy more octahedral sites with increasing La₂O₃ content. The produced samples showed a greenish-yellow color caused by the absorption band centered at ∼415 nm associated with the electronic transition ⁴A₂g(F)→2Eg(G). The ligand field effect highlighted the significance of La³⁺ cations in increasing the crystalline field intensity surrounding Cr³⁺ cations and reducing the nephelauxetic ratio, signifying enhanced covalent character between Cr³⁺ cations and neighboring ions. Moreover, the radiation shielding capabilities of the glassy system were analyzed and compared with standard shielding materials, confirming superior shielding performance in samples with the highest La₂O₃ content.

Dielectric properties, relaxation time and conduction behavior of MoO3 doped V2O5–ZnO–CuO glassy semiconducting system

Dielectric properties, relaxation time and conduction behavior of MoO3 doped V2O5–ZnO–CuO glassy semiconducting system

Analysis of luminescent properties of 40PbO–35Bi2O3–25Ga2O3 glasses doped with Er2O3

The Er3+ doped lead–bismuth–gallium oxide glasses were prepared by melt quenching technique. The spectral and luminescent properties were analyzed based on experimental and theoretical calculations. Analysis of Er3+ concentration dependences of density and electronic optical polarizability was carried out. The radiative lifetime values for 4S3/2 and 4F9/2 energy states were calculated using Judd-Ofelt theory. In the glassy system under study, the concentration quenching of state 4S3/2 was discovered at content of erbium ions above 0.869 × 1020 cm−3. It was also shown that 4F9/2 energy state was isolated from concentration effects and showed an increase in luminescence intensity with increasing concentration of activator ions. The luminescence quantum efficiency for transition 4S3/2 → 4I15/2 was about 40%, which allows us to consider this system as a glassy matrix effective for activation by rare-earth ions.

How caged motion in the contact layer enhances thermal tunneling across a liquid/solid interface

Ever more powerful and densely packed chips for applications like cryptocurrency mining and artificial intelligence generate such enormous heat fluxes that designers are pivoting from gas to liquid cooling to forestall damage from thermal runaway. Even with optimal flow patterns, however, the intrinsic thermal boundary resistance at the liquid/solid (L/S) interface poses an additional source of thermal impedance. There is a lingering misconception in the field that the higher the liquid contact density, the more frequent the L/S collision rate and the smaller the thermal slip length. Here we present an insightful counterexample based on nonequilibrium molecular dynamics simulations of a simple liquid confined between two face centered cubic crystals at different temperatures aligned with the [001], [011] or [111] facet plane. Measurements of various static and dynamic quantities of the contact layer reveal the ways in which long-range order, anisotropy of the L/S potential, and correlated motion act to reduce thermal boundary resistance. Systems with the smallest thermal slip length exhibit two distinct features: 2D caged motion with stringlike alignment of liquid particles, unlike that observed in glassy systems, and larger nonergodicity parameter with shorter, not longer, caging times. This trapping and release mechanism suggests a paradigm for the design of L/S interfaces to maximize thermal exchange across a classical L/S interface. Published by the American Physical Society 2024

Radiation shielding competence of SeTeSnIn chalcogenide glassy system: resistance against gamma irradiation

This paper reports the study of the high-energy radiation shielding characteristics of the STS glassy system. Further, the work investigates the effect of indium concentration on the high energy radiation shielding characteristics of the STS glassy system. For this purpose, a glassy Se78-xTe20Sn2Inx (x = 0, 2, 4, and 6) system was synthesized using a renowned melt quench technique whose density was measured through the Archimedes method. We have utilized an online platform, i.e., Phy-X/PSD software, to measure the different radiation shielding parameters of the SeTeSnIn glassy system. Several shielding parameters such as linear and mass attenuation coefficient, half value layer (HVL), mean free path (MFP), effective atomic number (Z eff ), effective electron density (N eff ), effective conductivity (C eff ), equivalent atomic number (Zeq), energy absorption build-up factor (EABF), exposure build-up factor (EBF), and fast neutron removal cross-section (FNRCS) have been measured in the energy range of 15 keV to 15 MeV.

Elastic Moduli, and Estimations of Some Physical, Thermal, and Optical Parameters of Ge-Se-As Glassy Systems with Improved Mechanical Strength

Employing the melt quench approach, glassy systems with the chemical composition Ge30Se(70-x)Asx have been synthesized. As the amount of arsenic increases, various physical, mechanical, thermal, optical parameters and some other aspects of elastic moduli have been assessed. The XRD pattern shows the amorphous characteristics of the inspected materials. The density of the glasses increases from 4.32 to 4.61 g-cm-3 whereas the molar volume declines from 19.32 to 18.62 cm3 mol-1 as the concentration of arsenic increases. The measured values of the ultrasonic velocities have been used to measure the elastic properties, such as the Shear, and longitudinal strains, Bulk modulus, Young's modulus, and Poisson's ratio of the synthesized glasses. The upsurge in the values of elastic moduli indicated the upgrading in the elastic properties of the materials. The outcomes are interpreted in terms of a profound structural change brought about by molecular rearrangement, which regulates the glass’s physical characteristics. The optical band gap energies are found to decrease from 2.17 to 1.86 eV due to the increase in Urbach energies from 040 to 0.64 eV with the incorporation of arsenic atom. The obtained results indicate the perspective of the as-synthesized thermally stable materials to be used in optoelectronic devices.

Effect of TiO₂ Addition on Elastic Moduli, Optical Bandgap, and Electrical Conductivity of xTiO₂-(0.30-x)Bi₂O₃-0.10ZnO-0.60TeO₂ Glassy Systems with Improved Thermal Stability

Glassy systems with the chemical composition xTiO2-(0.30-x)Bi2O3-0.10ZnO-0.60TeO2 (x = 0.05,0.10,0.15,0.20) have been synthesized using the melt quench approach. Numerous physical, electrical, optical, and other features of elastic moduli have been evaluated as titanium oxide concentration rises. The amorphous properties of the materials under inspection are displayed in the XRD pattern. As the concentration of arsenic rises, the glasses' density falls from 4.18 to 3.96 g/cm3, while their molar volume rises from 48.21 to 53.06 cm3mol-1. The elastic properties of the synthesized glasses, such as the shear (S) and longitudinal (L) stresses, bulk modulus (K), Young's modulus (Y), and Poisson's ratio (Pr), have all been measured using the measured values of the ultrasonic velocities. The increase in elastic moduli values showed that the materials' elastic qualities have been improved. The results are explained in terms of a significant structural alteration caused by molecular rearrangement, which controls the physical properties of the glass. The addition of titanium oxide is shown to cause a decrease in Urbach energies from 0.96 to 0.67 eV, which results in an increase in the optical band gap energies from 2.96 to 3.33 eV. DSC thermogram measurements reveal mechanically enhanced and thermally stable materials with potential for use in semiconducting devices.

Machine learning that predicts well may not learn the correct physical descriptions of glassy systems

The complexity of glasses makes it challenging to explain their dynamics. Machine learning (ML) has emerged as a promising pathway for understanding glassy dynamics by linking their structural features to rearrangement dynamics. Support vector machine (SVM) was one of the first methods used to detect such correlations. Specifically, a certain output of SVMs trained to predict dynamics from structure, the distance from the separating hyperplane, was interpreted as being linearly related to the activation energy for the rearrangement. By numerical analysis of toy models, we explore under which conditions it is possible to infer the energy barrier to rearrangements from the distance to the separating hyperplane. We observe that such successful inference is possible only under very restricted conditions. Typical tests, such as the apparent Arrhenius dependence of the probability of rearrangement on the inferred energy and the temperature, or high cross-validation accuracy do not guarantee success. Since even in such relatively simple toy models, prediction success of ML models does not necessarily translate into success of learning the underlying physics, we suggest that more careful investigations are needed when such claims are made. For this, we propose practical approaches for measuring the quality of the energy inference and for modifying the inferred model to improve the inference, which should be usable in the context of realistic datasets. Published by the American Physical Society 2024

Unifying the temperature dependent dynamics of glass formers.

Strong changes in bulk properties, such as modulus and viscosity, are observed near the glass transition temperature, Tg, of amorphous materials. For more than a century, intense efforts have been made to define a microscopic origin for these macroscopic changes in properties. Using transition state theory (TST), we delve into the atomic/molecular level picture of how microscopic localized unit relaxations, or "cage rattles," evolve to macroscopic structural relaxations above Tg. Unit motion is broken down into two populations: (1) simultaneous rearrangement occurs among a critical number of units, nα, which ranges from 1 to 4, allowing a systematic classification of glass formers, GFs, that is compared to fragility; and (2) near Tg, adjacent units provide additional free volume for rearrangement, not simultaneously, but within the "primitive" lifetime, τ1, of one unit rattling in its cage. Relaxation maps illustrate how Johari-Goldstein β-relaxations stem from the rattle of nα units. We analyzed a wide variety of glassy materials and materials with a glassy response using literature data. Our four-parameter equation fits "strong" and "weak" GFs over the entire range of temperatures and also extends to other glassy systems, such as ion-transporting polymers and ferroelectric relaxors. The role of activation entropy in boosting preexponential factors to high "unphysical" apparent frequencies is discussed. Enthalpy-entropy compensation is clearly illustrated using the TST approach.

Escaping Kinetic Traps Using Nonreciprocal Interactions.

Kinetic traps are a notorious problem in equilibrium statistical mechanics, where temperature quenches ultimately fail to bring the system to low energy configurations. Using multifarious self-assembly as a model system, we introduce a mechanism to escape kinetic traps by utilizing nonreciprocal interactions between components. Introducing nonequilibrium effects offered by broken action-reaction symmetry in the system pushes the trajectory of the system out of arrested dynamics. The dynamics of the model is studied using tools from the physics of interfaces and defects. Our proposal can find applications in self-assembly, glassy systems, and systems with arrested dynamics to facilitate escape from local minima in rough energy landscapes.

Complete realization of energy landscapes and non-equilibrium trapping dynamics in small spin glass and optimization problems

Energy landscapes are high-dimensional surfaces underlie all physical systems, which determine crucially the energetic and behavioral dependence of the systems on variable configurations, but are difficult to be analyzed due to their high-dimensional nature. Here we introduce an approach to reveal for the complete energy landscapes of spin glasses and Boolean satisfiability problems with a small system size, and unravels their non-equilibrium dynamics at an arbitrary temperature for an arbitrarily long time. Remarkably, our results show that it can be less likely for the system to attain ground states when temperature decreases, due to trapping in individual local minima, which ceases at a different time, leading to multiple abrupt jumps in the ground-state probability. For large systems, we introduce a variant approach to extract partially the energy landscapes and observe both semi-analytically and in simulations similar phenomena. This work introduces new methodology to unravel the energy landscapes and non-equilibrium dynamics of glassy systems, and provides us with a clear, complete and new physical picture on their long-time behaviors inaccessible by existing approaches.

(Ge2S8)100-xTex chalcogenide glasses: Physico-mechanical study for NIR optical devices

To better understand the variations in physical, mechanical, and electrical properties, (Ge2S8)100-xTex chalcogenide glasses have been synthesized. These glasses encompass a composition range of 0 ≤ x ≤ 12. The mechanical properties have been studied by determining the longitudinal (νL) and transverse (νT) ultrasonic velocities. A network structure evaluation with composition has been performed via parameters like coordination number (<Nr>), crosslinking density (DCL), glass transition temperature (Tg), etc. Also, the elastic parameters trend values have been associated with the decrease in the cohesive energy value of the system. An overall physical analysis of the Ge-S-Te systems reveals that the system's rigidity and the cross-linking density are decreasing. Within the temperature range of 300–420 K, the temperature dependency of the dark conductivity and photoconductivity has been investigated. The intensity-dependent photoconductivity is governed by a power law, with intensity (Iph = Gδ) with δ lying between 0.5 and 1. The photosensitivity values reveal that the glassy system may be suitable for applications in optoelectronic devices. A correlation among the parameters has been established by calculating elastic parameters and conductivity measurements and evaluating the network structure theoretically. The present efforts clarify the composition-structure dependence and relationship in the Ge-S-Te glass series.

Comparative study of physical properties of As2Se3 and (As2Se3)90Ge10 glassy alloys doped with metallic impurities

To examine the compositional and chemical effects on the glassy system, one must first understand its network structure. Alloying glassy systems cause significant conformal and configurational changes. The optical and physical parameters of As2Se3 and (As2Se3)90Ge10 glassy alloys doped with metallic impurities (X = Bi, Cd, Pb, Sb) have been evaluated. A comparison of the physical properties of glassy alloys has been made as the doping elements increase, i.e., from binary to ternary to quaternary system, and an effort has been made to correlate the optical and physical parameters. The optical density (Dop) and penetration depth (δ) have been calculated from the reported absorption coefficient (α) data. The mean coordination number (<r>) and the number of floppy modes (Mf) calculations show that the floppy regions are decreasing, and hence, the rigidity is increasing when As–Se is doped with Ge and As–Se-Ge is doped with X. The density (ρ) and packing density (PD) have also been evaluated, which are interrelated to the parameters like refractive index (n) and δ. Cohesive energy (CE), mean bond energy (<E>), and glass transition temperature (Tg) values give an insight into the stability and average crosslinking of the system with alloying. The conduction and valence band potentials have supported the optical bandgap (Egopt) values variation.