Glass Formation Process Research Articles

Glass transition and crystallization of Se95Te5 chalcogenide glassy semiconductor

The study is dedicated to the investigation of thermo-physical characteristics of Se95Te5 chalcogenide glassy semiconductor during its glass formation and crystallization processes, employing various scanning rates of 5, 10, 15 and 20 K/min in non-isothermal modes through DSC measurement. Analysis of the structural relaxation kinetics involves the Kissinger’s, Augis and Bennett's, as well as Matusita’s approaches. Experimental data yield contains the determination of crucial parameters such as glass transition (𝑇𝑇𝑔𝑔), crystallization(𝑇𝑇𝑐𝑐), and melting temperatures alongside factors like reduced temperature of glass transition (𝑇𝑇𝑟𝑟𝑟𝑟), Hruby’s parameter (𝐾𝐾𝑔𝑔𝑔𝑔), fragility index (𝐹𝐹𝑖𝑖), Avrami exponents (n, m), glass transition (140.24 kJ/mol) and crystallization (Ec = 95.11 kJ/mol) energies, respectively. The results confirm that Se95Te5 chalcogenide system as an efficient glass former. Matusita’s method reveals that the crystallization mechanism (n = 2.51, m = 1.9) corresponds to volumetric nucleation with two-dimensional growth.

Investigating the influence of medium range order defects on shear instability in Cu64Zr36 metallic glass

The occurrence of shear instability in metallic glasses is profoundly influenced by the spatial perturbation of material properties. Despite the considerable research on the origin of shear transformation zones (STZ), it remains a challenge to understand the behavior from a structural perspective. In this study, extensive molecular simulations (MD) and synchrotron diffraction were employed to characterize the structural features of medium-range order (MRO) defects in Cu64Zr36 metallic glass. These defects manifest as line-like interruptions in the connections between full icosahedral clusters. And it was also observed that the size and content of these defects are closely related to the history of the glass formation process. Moreover, we explored the contribution of these MRO defects, which are comparable in size to the STZ, in the genesis of shear instability. We uncovered that a large strain gradient exists in these regions under external loads, providing a convenient pathway for STZ activation. Notably, the generation of MRO defects are also going on as the STZ evolves. These insightful findings provide valuable insights and offer a promising avenue for the design and development of advanced metallic glass materials with enhanced structural integrity.

An isochoric optical platform for interrogation of aqueous glass formation processes.

Aqueous vitrification (glass formation) processes are integral to modern cryopreservation, but experimental methods by which to study them are limited, particularly at the mL volume scales relevant to many biomedical applications. Here, we introduce an inexpensive custom optical platform, the isochoric vitrification cryo-macroscope (or "isovitriscope"), to supplement standard techniques with new qualitative and quantitative data streams. The platform consists of an LED light source, a isochoric (constant-volume) chamber with sapphire optical windows, and a camera, which can operate in two modes. One mode enables sharp visual observation of the glass transition and other low-temperature physical processes, including cracking, annealing, ice and hydrate crystallization, cavity formation, melting, etc. The other mode enables tracking of the optical temperature-evolution of the system via recorded light intensity, which we demonstrate may be used to measure the onset glass transition temperature with accuracy similar to differential scanning calorimetry (DSC), and to identify the temperature coordinates of other phase change events. The isovitriscope thus offers a single device combining the phenomenological insight of conventional visual inspection with the quantitative insight of techniques like calorimetry, at the >1 mL volume scales increasingly relevant to cryopreservation applications. To demonstrate uses of the isochoric optical platform, we herein conduct a series of observational studies examining the rich multi-phase phenomena at play during isochoric vitrification of binary cryoprotectant solutions; the effect of surface wettabilities on crack formation in the glassy state; the analogy between differential calorimetric and optical analysis; and more. In summary, the isochoric vitrification cryo-macroscope, or isovitriscope, adds a valuable new tool for the study of aqueous vitrification processes.

Role of additive size in the segmental dynamics and mechanical properties of cross-linked polymers.

Thermoset materials often involve the addition of molecular and nanoparticle additives to alter various chemo-physical properties of importance in their ultimate applications. The resulting compositional heterogeneities can lead to either enhancement or degradation of thermoset properties, depending on the additive chemical structure and concentration. We tentatively explore this complex physical phenomenon through the consideration of a model polymeric additive to our coarse-grained (CG) thermoset investigated in previous works by simply varying the size of additive segments compared to those of polymer melt. We find that the additive modified thermoset material becomes chemically heterogeneous from additive aggregation when the additive segments become much smaller than those of the thermoset molecules, and a clear evidence is observed in the spatial distribution of local molecular stiffness estimated from Debye-Waller factor 〈u2〉. Despite the non-monotonic variation trends observed in dynamical and mechanical properties with decreasing additive segmental size, both the structural relaxation time and moduli (i.e., shear modulus and bulk modulus) exhibit scaling laws with 〈u2〉. The present work highlights the complex role of additive size played in the dynamical and mechanical properties of thermoset polymers, which should provide a better understanding for the glass formation process of cross-linked polymer composites.

Effect of chemical short-range ordering on thermodynamics, structure, and dynamics of ZrCu-based metallic glass-forming liquids

Chemical-ordering in metallic liquid alloys affects important structural, thermodynamic, and dynamical factors governing the kinetics of the glass formation process and the glass-forming ability. The present study on Zr50Cu50, Zr50Cu45Al5, and Zr50Cu45Ag5 metallic glass-forming liquids reveal that minor addition of Al/Ag in Zr50Cu50 leads to different chemical short-range orders due to the hetero-coordination tendency of Al in Zr50Cu45Al5 and homo-coordination tendency of Ag in Zr50Cu45Ag5. Different chemical short-range ordering causes qualitatively different topological short-range orders in the two ternary alloys. Results of inherent structure energy and excess entropy indicate modification of the potential energy landscape such that the local minima (metabasins) on the landscape of Zr50Cu45Al5 become deeper and less rugged, whereas the metabasins become shallower and more rugged in Zr50Cu45Ag5. Single-particle dynamics investigations clearly demonstrate the effect of difference in the chemical-ordering, topological short-range order, and the potential energy landscape on the atomic diffusion, structural relaxation, and dynamic heterogeneities in the ternary alloys. It signifies that the dynamics of the studied glass-forming alloys is closely linked with the structure and thermodynamics. The study also provides a very useful insight of the correlation between the chemical-ordering and the short-time dynamical features in the studied metallic glass-forming liquids.

Processes of Glass Formation in Fullerene Mixtures

Processes of Glass Formation in Fullerene Mixtures

Glass formation processes in fullerene mixtures

The local structural features of the A20B80 fullerene mixture (where A = C60 and B = C70) are studied by the molecular dynamics simulations for a wide temperature range, including the phase of an equilibrium liquid phase and a supercooled melt, in order to elucidate the mechanism of formation of the icosahedral short-range order in binary molecular liquids. Structural and cluster analyzes revealed the presence of icosahedral clusters in the supercooled melt phase and determined the critical glass transition temperature.

INFLUENCE OF B2O3 ON THE INTERACTION IN THE SiO–GeO2 SYSTEM

The influence of the B2O3 additive on the nature of the interaction in the SiO–GeO2 system was investigated by X-ray diffraction and IR transmission spectroscopy. The nature of the diffractograms of the SiO–GeO2–B2O3 system with a composition of 1:1:0.5 and 1:1:1 corresponds to the presence of SiO2 phases of hexagonal modification (quartz) and GeO2 of various modifications, as well as, possibly, a crystalline B2O3 phase. The exact value of the content of the reaction products and initial components could not be determined due to the significant content of the X-ray amorphous component of unknown composition. The broadening of the diffraction peaks and the presence of a distinct halo testify to the benefit of the processes of nanostructuring and glass formation. However, the absence of elemental germanium in the SiO–GeO2–B2O3 system, in contrast to the SiO–GeO2 system, was clearly established. The nature of the IR transmission spectra of samples with different content of B2O3 additive differ significantly from each other. Thus, the IR transmission spectra of the sample with a composition of 1:1:0.5 contain weak absorption bands due to the oscillations of the B–O bonds; instead, they reveal periodic oscillations characteristic of nanostructured systems. In the spectra of the sample with a composition of 1:1:1, the absorption bands due to the oscillations of the B–O bonds are very distinct, but there are no oscillations. Therefore, the addition of B2O3 probably accelerates the formation of Germanium monoxide, which in turn reacts with the B2O3 additive and possibly with SiO2 as one of the reaction products. Testing of samples of the SiO–GeO2–B2O3 system by the method of thermal evaporation in a vacuum revealed the advantages of the sample with a composition of 1:1:1 in the ability to form a strong and durable coating. It was possible to determine the refractive index for it, which is 1.93 at a wavelength of 1000 nm. Instead, the coating obtained from the 1:1:0.5 composition sample turned out to be unstable. A conclusion was made about the need for further optimization of the composition and synthesis conditions to obtain materials with the required parameters.

Concentration dependence of microstructural evolution of Zr-Pt liquid alloys: A molecular dynamics study

The concentration dependence of the atomic structure and glass formation process of Zr100-xPtx (10 ≤ x ≤ 60) alloys were investigated by molecular dynamics simulations in this study. The agreement between the structural functions and the experimental data showed that the local order is reliably predicted. It was observed that the Zr40Pt60 alloy has the highest glass transition temperature and the fraction of crystal-like clusters. Common neighbor analysis revealed that the icosahedra and icosahedra-like clusters are more frequent for x < 50 concentrations, while bcc-like clusters are effective for x ≥ 50. It was seen that the local environment around Pt atoms would be more flexible, while Zr atoms would more easily adopt a preferential local packing according to their preferences. Present findings suggest that the strong chemical affinity between Zr and Pt plays an influential role in the nucleation of local structure in the system, and the addition of Pt weakens the icosahedra short-range order.

Molecular Dynamics Modeling of SiO2 Melts and Glass Formation Processes

Molecular Dynamics Modeling of SiO2 Melts and Glass Formation Processes

Molecular Dynamics Modeling of SiO2 Melts and Glass Formation Processes

Molecular dynamics (MD) with ReaxFF potentials is used to study the melting process of quartz and cristobalite together with the amorphous structures obtained at different stages of melting by cooling the melt. The long-term preservation of an excess of eight-membered rings inherited from the crystalline phase is found in the quartz melts, while in the cristobalite melts, the similar preservation of six-membered rings is not observed. Thus, it can be stated that the quartz melts and glasses obtained from them have structural memory, in contrast to cristobalite melts. An increase in the number of four-membered rings with increasing temperature is revealed. A number of other features of the obtained amorphous structures, which we consider as models for glasses, are discussed.

Effects of cooling rate on the glass formation process and the microstructural evolution of Silver mono-component metallic glass

In this study, using molecular dynamics simulations in combination with the embedded-atom approach, we investigate the effect of cooling rate on the microstructural evolution and the glass formation process of Silver monatomic metallic glass. In order to accomplish our investigation, we have utilised a variety of analytical techniques, including the pair distribution function, the bond angle distribution, the Voronoi tessellation analysis, the coordination number, and the five-fold symmetry. The splitting of the second peak in the pair distribution function during the cooling process confirms that glass formation occurs. Via the Went-Abraham parameter, we have found that a faster cooling rate leads to a higher glass transition temperature Tg, and a less relaxed glass has a lower density due to its greater free volume and disordered structure. In the same context, the bond angle distribution revealed that the cooling rate clearly influences the icosahedral short-range order in the quenched system, and the Voronoi tessellation analysis indicated that the percentage of mixed-like and icosahedral-like clusters grows as the cooling rate increases. Furthermore, the coordination number indicated that when the temperature drops throughout the cooling process, the local environment and topological structure of the amorphous Silver change. Lastly, we have also revealed that the five-fold symmetry controls the formation of the amorphous structure and that the highest cooling rate yields the greatest amount of icosahedral-like clusters in the vitreous phase, implying that fast cooling rates subserve the formation of glassy states with icosahedral-like features.

Structure formation processes in fullerene mixtures

Glass formation processes in condensed matter are characterized by some specific short-range order changes in the arrangement of particles (atoms/molecules/ions). So, the short-range structural order in supercooled liquids and glasses is characterized by fivefold symmetry in the arrangement of particles, often referred to as icosahedral (ideal or distorted) short-range order. This article is devoted to the study of local structural features of the supercooled melt of the A20B80 fullerene mixture (where A = C60 and B = C70) obtained under various cooling protocols in order to elucidate the mechanism of formation of the icosahedral short-range order in binary molecular liquids. Comprehensive studies of the properties of a fullerene mixture melt were carried out using large-scale molecular dynamics simulations followed by structural and cluster analysis. The crystallization temperature and the critical glass transition temperature of the system were calculated to be T_m~1439 K and T_c~1238 K, respectively. It has been established that the crystallization of a binary fullerene mixture proceeds according to the polycrystalline scenario with the formation of clusters with fcc and hcp symmetries. It is shown that in a supercooled fullerene mixture, the short-range icosahedral order is formed by an insignificant number of ideal icosahedral clusters and a certain set of distorted icosahedral clusters, the fraction of which remains practically unchanged at temperatures below the critical glass transition temperature. Keywords: molecular dynamics, fullerenes, short-range order, structural ordering.

Процессы структурообразования в фуллереновых смесях

Glass formation processes in condensed matter are characterized by some specific short-range order changes in the arrangement of particles (atoms/molecules/ions). So, the short-range structural order in supercooled liquids and glasses is characterized by fivefold symmetry in the arrangement of particles, often referred to as icosahedral (ideal or distorted) short-range order. This article is devoted to the study of local structural features of the supercooled melt of the A20B80 fullerene mixture (where A = C60 and B = C70) obtained under various cooling protocols in order to elucidate the mechanism of formation of the icosahedral short-range order in binary molecular liquids. Comprehensive studies of the properties of a fullerene mixture melt were carried out using large-scale molecular dynamics simulations followed by structural and cluster analysis. The crystallization temperature and the critical glass transition temperature of the system were calculated to be Tm ≈ 1439 K and Tc ≈ 1238 K, respectively. It has been established that the crystallization of a binary fullerene mixture proceeds according to the polycrystalline scenario with the formation of clusters with fcc and hcp symmetries. It is shown that in a supercooled fullerene mixture, the short-range icosahedral order is formed by an insignificant number of ideal icosahedral clusters and a certain set of distorted icosahedral clusters, the fraction of which remains practically unchanged at temperatures below the critical glass transition temperature.

Магнитные свойства стекол, синтезированных на основе горных пород различного генезиса

The structural-phase, chemical composition and magnetic properties of artificial glasses obtained by high-temperature melting of rock mixtures of different genesis: volcanogenic-sedimentary rocks, quartzitic shales, psamite-silt-pelitic complexes were studied. Different in duration cooling and glass transition conditions were used for glass synthesis. The magnetic state of the iron-containing phase and the analysis of the presence and contribution of iron oxides to the magnetic properties were assumed to be the characteristic criterion determining the parameters of the glass formation process. It was shown that the total iron content in artificial glasses depends exclusively on the composition of the initial charge. In this case, the iron-containing component is mainly determined by sedimentary rocks. The formation of magnetic minerals is determined both by the composition of the charge and by the rate of cooling of the melt. During “fast” cooling, the formed magnetic particles are mostly (up to 90% or more of the total content of the magnetic phase in the sample) in a superparamagnetic state. During “slow” cooling, a mixture of particles of different sizes and, accordingly, in different magnetic states is formed: from superparamagnetic to low-domagnetic. The ferrimagnetic phase crystallizing in artificial glasses is represented by chemically heterogeneous aggregates of iron oxides, mainly non-stoichiometric magnetite.

Molecular dynamics simulations of glass formation, structural evolution and diffusivity of the Pd-Si alloys during the rapid solidification process

The atomic structure, glass formation process and diffusion mechanism of Pd100-xSix (x = 10, 20, 30, 40 and 50) alloys during rapid solidification have been investigated by molecular dynamics simulations using embedded atom method potentials. The structure factors, total (or Pd90Si10) and partial pair distribution functions calculated for Pd80Si20 bulk metallic glass are in good agreement with the experimental/other data. Bond angle distribution function, Honeycutt-Andersen index and Voronoi tessellation analysis have revealed that the increasing Si amount caused a decrease in the number of icosahedral-like clusters and an increase in the number of crystal-like clusters. The majority of icosahedral-like clusters in the systems are mostly composed of Pd-centered clusters, suggesting that Pd has an effective role in the glass formation process in Pd-Si systems. It has been observed that the mobility of Si atoms decreases in environments with more Pd atoms. The critical temperature and T0 temperature for Pd-Si liquids have been determined from the self-diffusion coefficients using the mode-coupling theory and the Vogel-Fulcher-Tammann law, respectively. The present findings show us that the Pd70Si30 compound has a critical importance in terms of the glass formation process, which is consistent with experimental observations. We hope that the results will contribute to understanding the Si effect on the atomic local structure of Pd-Si systems and will encourage research on many properties of these systems, such as their mechanical properties.

Designing Glass and Crystalline Phases of Metal-Bis(acetamide) Networks to Promote High Optical Contrast.

Owing to their high tunability and predictable structures, metal-organic materials offer a powerful platform to study glass formation and crystallization processes and to design glasses with unique properties. Here, we report a novel series of glass-forming metal-ethylenebis(acetamide) networks that undergo reversible glass and crystallization transitions below 200 °C. The glass-transition temperatures, crystallization kinetics, and glass stability of these materials are readily tunable, either by synthetic modification or by liquid-phase blending, to form binary glasses. Pair distribution function (PDF) analysis reveals extended structural correlations in both single and binary metal-bis(acetamide) glasses and highlights the important role of metal-metal correlations during structural evolution across glass-crystal transitions. Notably, the glass and crystalline phases of a Co-ethylenebis(acetamide) binary network feature a large reflectivity contrast ratio of 4.8 that results from changes in the local coordination environment around Co centers. These results provide new insights into glass-crystal transitions in metal-organic materials and have exciting implications for optical switching, rewritable data storage, and functional glass ceramics.

Fabrication of glass ceramic sealants with ceramic fiber filler for solid oxide fuel cells

In this study, ceramic fibers are used as a filler material for glass ceramic sealant in solid oxide fuel cells to improve the thermal cycle behavior. Beside the bare glass ceramic sealant for comparison, multilayered sealants with different ceramic fiber contents are fabricated to investigate the effect of ceramic fiber quantity also. The mechanical performances of the samples are measured via tensile tests by placing them between two metallic interconnector plates after the glass formation process as well as after 1, 5 and 10 thermal cycles. The results show that the mechanical strength in general tends to decrease with increasing the ceramic filler content, which can be attributed to poor adhesion due to reduced glass ceramic composition. On the other hand, thermal cycle behavior of the samples with ceramic fibers is found to be improved at some extend. This may be due to the behavior of ceramic filler network and relatively slow crystallization with increasing the amount of the filler as proven by microstructural observations. Especially for the sample including 4 ceramic fiber interlayers each having 0.030 g ceramic fibers, the mechanical strength shows an increasing trend with the number of thermal cycles.

Dual Cluster Model for Medium-Range Order in Metallic Glasses

The atomic structure of medium-range order in metallic glasses is investigated by using molecular dynamics (MD) simulations. Glass formation processes were simulated by rapid cooling from liquid phases of a model binary alloy system of different-sized elements. Two types of short-range order of atomic clusters with the five-fold symmetry are found in glassy phases: icosahedral clusters (I-clusters) formed around the smaller-sized atoms and Frank–Kasper clusters (i.e., Z14, Z15, and Z16 clusters (Z-clusters)) formed around the bigger-sized atoms. Both types of clusters (I-and Z-clusters) are observed even in liquid phases and the population of them goes up as the temperature goes down. A considerable atomic size difference between alloying elements would enhance the formation of both the I- and Z-clusters. In glassy phases, the I- and Z-clusters are mutually connected to form a complicated network, and the network structure becomes denser as the structural relaxation goes on. In the network, the medium-range order is mainly constructed by the volume sharing type connection between I- and Z-clusters. Following Nelson’s disclination theory, the network structure can be understood as a random network of Z-clusters, which is complimentarily surrounded by another type of network formed by I-clusters.

Unfolding kinetic fragility in relaxor ferroelectrics

The fragility parameter is one of the most important material constants that is extensively used in glass science, playing a central role in the enhancement of understanding the glass formation process of disordered systems. Although fragility has been widely used, this concept has never been precisely defined and evaluated in relaxor ferroelectrics. Here, we have filled up this scientific gap. Based on a generalized Vogel–Fulcher–Tammann equation, the fragility parameter is introduced for relaxor ferroelectrics. The new formulation has been quantitatively assessed by combining dielectric spectroscopy and pyroelectric measurements on canonical relaxors. A clear correlation between the fragility and a new local structural heterogeneity-related order parameter elucidates new information about the ferroelectric order of relaxor ferroelectrics. This may open a new pathway to disentangle relaxation phenomena in other relaxor ferroics.