Motivated by old experiments on colloidal suspensions, we report molecular dynamics simulations of assemblies of hard spheres, addressing crystallization and glass formation. The simulations cover wide ranges of polydispersity s (standard deviation of the particle size distribution divided by its mean) and particle concentration. No crystallization is observed for s > 0.07. For 0.02 < s < 0.07, we find that increasing the polydispersity at a given concentration slows down crystal nucleation. The main effect here is that polydispersity reduces the supersaturation since it tends to stabilise the fluid but to destabilise the crystal. At a given polydispersity (< 0.07) we find three regimes of nucleation: standard nucleation and growth at concentrations in and slightly above the coexistence region; "spinodal nucleation", where the free energy barrier to nucleation appears to be negligible, at intermediate concentrations; and, at the highest concentrations, a new mechanism, still to be fully understood, which only requires small re-arrangement of the particle positions. The cross-over between the second and third regimes occurs at a concentration, around 58% by volume, where the colloid experiments show a marked change in the nature of the crystals formed and the particle dynamics indicate an "ideal" glass transition.
In a recent article, Schmelzer and Tropin [Entropy 20 [2] 103 (2018)] presented an unfounded, confusing critique of several aspects of modern glass science. Relying on pre-Socratic Greek philosophy and state-of-the-art scientific understanding from the 1920s-1930s, Schmelzer and Tropin propagate an antiquated view of glass physics that is at odds with well-accepted knowledge in the field from both theory and experiments conducted in the post-World War II era. The objective of this short letter is to elucidate and extinguish their critique. This rebuttal is directed to our colleagues and especi…
Engineering phase change materials (PCM) to realize superior data storage devices requires a detailed understanding of crystallization kinetics and its temperature dependence. The temperature dependence of crystallization differs distinctly between crystallizing from the glassy phase and the undercooled liquid (UCL). Hence, knowing the phase from which crystallization occurs is necessary for predicting the switching ability. Here, we measure the glassy dynamics and crystallization kinetics using calorimetry for heating rates spanning over six orders of magnitude. Our results show that the prom…
Crystallization of metallic glass as a grain-boundary nucleated process: experimental and theoretical evidence for the grain structure of metallic glasses
Crystallization within the discrete spheres of a block copolymer mesophase was studied by time-resolved x-ray scattering. The cubic packing of microdomains, established by self-assembly in the melt, is preserved throughout crystallization by strong interblock segregation even though the amorphous matrix block is well above its glass transition temperature. Homogeneous nucleation within each sphere yields isothermal crystallizations which follow first-order kinetics, contrasting with the sigmoidal kinetics normally exhibited in the quiescent crystallization of bulk polymers.
In supercooled liquids, vitrification generally suppresses crystallization. Yet some glasses can still crystallize despite the arrest of diffusive motion. This ill-understood process may limit the stability of glasses, but its microscopic mechanism is not yet known. Here we present extensive computer simulations addressing the crystallization of monodisperse hard-sphere glasses at constant volume (as in a colloid experiment). Multiple crystalline patches appear without particles having to diffuse more than one diameter. As these patches grow, the mobility in neighbouring areas is enhanced, cre…
The rheological properties of highly concentrated suspensions of hard-sphere particles are studied with particular reference to the rheological response of shear induced crystals. Using practically monodisperse hard spheres, we prepare shear induced crystals under oscillatory shear and examine their linear and non-linear mechanical response in comparison with their glassy counterparts at the same volume fraction. It is evident, that shear-induced crystallization causes a significant drop in the elastic and viscous moduli due to structural rearrangements that ease flow. For the same reason the …
Transparent glasses of BaNaB9O15 (BNBO) were fabricated via the conventional melt-quenching technique. The amorphous and the glassy nature of the as-quenched samples were respectively, confirmed by X-ray powder diffraction (XRD) and differential scanning calorimetry (DSC). The glass transition and crystallization parameters were evaluated under non-isothermal conditions using DSC. The correlation between the heating rate dependent glass transition and the crystallization temperatures was discussed and deduced the Kauzmann temperature for BNBO glass-plates and powdered samples. The values of th…
The present study reports Al induced crystallization (AIC) of amorphous (a)-SiGe in Al-Ge-Si ternary system at low temperature ~ 350 degree C. In addition to crystallization, the isothermal annealing of a-SiGe/AlOx/Al/corning-glass (CG) structure was found to be accompanied by an Al induced layer exchange (ALILE) phenomenon. The evolution of residual stress in the Al layer during isothermal annealing is evaluated using X-ray diffraction based technique to ascertain the role of stress in the ALILE process. A corroboration of the stress with the growth kinetics, analyzed using Avrami theory of p…
The local organisation of a simulated glass-forming mixture due to Kob and Andersen is analysed. Evidence is presented for a structural transition from triangulated coordination polyhedra to cubic as the number fraction of the smaller species B increases towards equimolar. The impact of the change on the partial radial distribution function g-{BB}(r) is established. The dependence of the crystallisation rate on the composition is determined and the related to the observed structural changes.
Using Monte Carlo simulations we study crystallization in the three-dimensional Ising model with four-spin interaction. We monitor the morphology of crystals which grow after placing crystallization seeds in a supercooled liquid. Defects in such crystals constitute an intricate and very stable network which separate various domains by tensionless domain walls. We also show that the crystallization which occurs during the continuous heating of the glassy phase takes place at a heating-rate dependent temperature.
Using molecular simulations, we shed light on the mechanism underlying crystal nucleation in metal alloys and unravel the interplay between crystal nucleation and glass transition, as the conditions of crystallization lie close to this transition. While decreasing the temperature of crystallization usually results in a lower free energy barrier, we find an unexpected reversal of behavior for glass-forming alloys as the temperature of crystallization approaches the glass transition. For this purpose, we simulate the crystallization process in two glass-forming Copper alloys, $Ag_6Cu_4$, which h…
An aluminoborosilicate glass, containing high amount of rare earth (RE) accordingly to the following composition 50.68 SiO2 - 4.25 Al2O3 - 8.50 B2O3 - 12.19 Na2O - 4.84 CaO - 3.19 ZrO2 - 16.35 RE2O3 (wt.%), is currently under study for the immobilization of nuclear waste solutions. In this work, we wanted to investigate the effect of changing the RE cation type on the glass structure and on its crystallization behavior. For this purpose, a glass series was elaborated in which the nature of the RE is varying from lanthanum to lutetium. In this glass series, only little effect was observed on th…
Crystallization and vitrification are two different routes to form a solid. Normally these two processes suppress each other, with the glass transition preventing crystallization at high density (or low temperature). This is even true for systems of colloidal hard spheres, which are commonly used as building blocks for novel functional materials with potential applications, e.g. photonic crystals. By performing Brownian dynamics simulations of glassy systems consisting of mixtures of active and passive hard spheres, we show that the crystallization of such hard-sphere glasses can be dramatical…
A comparative study on as cast and annealed rare earth bulk metallic glass (BMG) with composition Tb36Sm20Al24Co20 has been carried out by magnetization measurements. The as cast amorphous sample shows non-ergodic magnetization but does not show the behavior expected from magnetic glass. After annealing, the partially crystallized BMG shows this magnetic glass behavior. This is confirmed by the established measurement protocol of cooling and heating in unequal fields (CHUF).
A complex rare-earth rich aluminoborosilicate glass has been proved to be a good candidate for the immobilization of new high level radioactive wastes. A simplified seven-oxides composition of this glass was selected for this study. In this system, sodium and calcium cations were supposed in other works to simulate respectively all the other alkali (R+=Li+, Rb+, Cs+) and alkaline-earth (R'2+=Sr2+, Ba2+) cations present in the complex glass composition. Moreover, neodymium or lanthanum are used here to simulate all the rare-earths and actinides occurring in waste solutions. In order to study th…
Competing crystallization pathways and cold crystallization kinetics in 10OS5 liquid crystal
Institute of Nuclear Physics, Polish Academy of Sciences（波兰科学院核物理研究所）；Faculty of Science, University of Siedlce（谢德尔采大学理学院）；Research Center for Thermal and Entropic Science, Graduate School of Science, Osaka University（大阪大学理学研究科热与熵科学研究中心）
In many technical applications, but also in natural processes like ice nucleation in clouds, crystallization proceeds in the presence of stresses and flows, hence the importance to understand the crystallization mechanism in simple situations. We employ molecular dynamics simulations to study the crystallization kinetics of a nearly hard sphere liquid that is weakly sheared. We demonstrate that shear flow both enhances and suppresses the crystallization kinetics of hard spheres. The effect of shear depends on the quiescent mechanism: suppression in the activated regime and enhancement in the d…
Abrupt crystallization from shock-compressed CaSiO3 glass
Graduate School of Engineering, The University of Osaka（大阪大学研究生院工学研究科）；School of Science, Wuhan University of Technology（武汉理工大学理学院）；Institute of Laser Engineering, The University of Osaka（大阪大学激光工程研究所）；Nevada Extreme Conditions Laboratory, University of Nevada, Las Vegas（内华达大学拉斯维加斯分校极端条件实验室）；RIKEN SPring-8 Center（理化学研究所SPring-8中心）；Graduate School of Science, Osaka Metropolitan University（大阪公立大学理学研究科）
Poly(ethylene terephthalate) (PET) is a semi--crystalline polymer that can be crystallized to different degrees heating from the amorphous state. Even when primary crystallization has been completed, secondary crystallization can take place with further annealing and modify the characteristics of the amorphous interlamellar phase. In this work we study the glass transition of highly crystallized PET and in which way it is modified by secondary crystallization. Amorphous PET samples were annealed for 4 hours at temperatures between 140C and 180C. The secondary crystallization process was monito…
Below the melting temperature $T_m$ crystals are the stable phase of typical elemental or molecular systems. However, cooling down a liquid below $T_m$, crystallization is anything but inevitable. The liquid can be supercooled, eventually forming a glass below the glass transition temperature $T_g$. Despite their long lifetimes and the presence of strong barriers that produces an apparent stability, supercooled liquids and glasses remain intrinsically metastable state and thermodynamically unstable towards the crystal. Here we investigated the isothermal crystallization kinetics of the prototy…
Dynamic compression of glassy GeO$2$ up to the TPa range and first observation of shock induced crystallization
European Synchrotron Radiation Facility（欧洲同步辐射装置）；Politecnico di Milano（米兰理工大学）；Laboratoire pour l’Utilisation des Lasers Intenses, Ecole Polytechnique, CNRS, Commissariat à l’Energie Atomique, Sorbonne Université（高强度激光利用实验室，巴黎综合理工学院，法国国家科学研究中心，法国原子能和替代能源委员会，索邦大学）；CEA, DAM, DIF（法国原子能和替代能源委员会，达姆研究部，集成设施）；Université Bordeaux, CNRS, CEA, CELIA, UMR 5107（波尔多大学，法国国家科学研究中心，法国原子能和替代能源委员会，CELIA联合研究单位）
Upcycling solar glass into Ce-doped oxyfluorides: spectroscopic and crystallization properties
Universidade Tecnológica Federal do Paraná（巴西联邦技术大学巴拉那分校）；Universidade Estadual de Maringá（马里纳加州立大学）；Laboratoire CEMHTI, UPR 3079-CNRS（法国国家科学研究中心CEMHTI实验室）
We determined bulk crystal nucleation rates in aqueous suspensions of charged spheres at low metastability. Experiments were performed in dependence on electrolyte concen-tration and for two different particle number densities. The time-dependent nucleation rate shows a pronounced initial peak, while post-solidification crystal size distributions are skewed towards larger crystallite sizes. At each concentration, the nucleation rate density initially drops exponentially with increasing salt concentration. The complete data set, however, shows an unexpected scaling of the nucleation rate densit…
Li1.5Al0.5Ge1.5(PO4)3 (LAGP) is among the most promising solid electrolytes for the next generation all-solid-state lithium batteries. However, preparing LAGP electrolytes is timeand energy-intensive. In this work, LAGP glassy powders were sintered and crystallized in 180 seconds by ultrafast high-temperature sintering (UHS) under conditions attractive for continuous industrial processes (i.e., ambient pressure and atmosphere). The fast heating rates characteristic of UHS significantly delay crystallization, potentially decoupling crystallization and sintering. Furthermore, EIS characterizatio…
We simulate a strongly size-disperse hard-sphere fluid confined between two parallel, hard walls. We find that confinement induces crystallization into n-layered hexagonal lattices and a novel honeycomb-shaped structure, facilitated by fractionation. The onset of freezing prevents the formation of a stable glass phase and occurs at much smaller packing fraction than in bulk. Varying the wall separation triggers solid-to-solid transitions and a systematic change of the size-distribution of crystalline particles, which we rationalize using a semi-quantitative theory. We show that the crystalliza…
A bulk metallic glass forming alloy is subjected to shear flow in its supercooled state by compression of a short rod to produce a flat disc. The resulting material exhibits enhanced crystallization kinetics during isothermal annealing as reflected in the decrease of the crystallization time relative to the non-deformed case. The transition from quiescent to shear-accelerated crystallization is linked to strain accumulated during shear flow above a critical shear rate $\dotγ_c\approx 0.3$ s$^{-1}$ which corresponds to Péclet number, $Pe\sim\mathcal{O}(1)$. The observation of shear accelerated …
Core optics components for high precision measurements are made of stable materials, having small optical and mechanical dissipation. The natural choice in many cases is glass, in particular fused silica. Glass is a solid amorphous state of material that couldn't become a crystal due to high viscosity. However thermodynamically or externally activated stimulated local processes of spontaneous crystallization (known as devitrification) are still possible. Being random, these processes can produce an additional noise, and influence the performance of such experiments as laser gravitational wave …
Nucleation and growth of crystal in an oxide glass was studied in a Si B Al Zr Nd Ca Na O system. The nucleation and growth process was monitored by thermal analysis and isothermal experiments. For the Ca sample the crystallization is homogeneous in the bulk showing a slow increase of crystallinity as temperature increases. The Na rich sample on the other hand go through several crystallization process in the bulk or from the surface, leading to bigger crystals. The activation energy of the viscous flow and the glass transition are of same magnitude when that of crystallization is a lot smalle…
Nuclear spent fuel reprocessing generates high level radioactive waste with high Mo concentration that are currently immobilized in borosilicate glass matrices containing both alkali and alkaline-earth elements [1]. Because of its high field strength, Mo6+ ion has a limited solubility in silicate and borosilicate glasses and crystallization of alkali or alkaline-earth molybdates can be observed during melt cooling or heat treatment of glasses [2-4]. Glass composition changes can significantly modify the nature and the relative proportions of molybdate crystals that may form during natural cool…
Study of condensed matter in certain extreme conditions allows one to better understand the mechanisms of microscopic structural transformations and to develop materials with completely new mechanical properties. In the present work, we study the structure and crystallization kinetics of bulk metallic glass (BMG) Ni$_{62}$Nb$_{38}$. We show that this BMG is rapidly crystallized under the combined effect of shear deformation and ultrahigh pressure. A threshold pressure required to initiate the formation of a stable crystalline phase is revealed. Shear deformation and pressure lead to the phase …
Metals in amorphous state are promising for the use as structural materials due to their superior properties related to the absence of grain boundaries and dislocations.Obtaining the amorphous state requires quenching with a high cooling rate.In conventional technologies,this is the reason for a considerable size limitation hindering application of amorphous alloys.Additive manufacturing (AM) is free of the size limitation.The so-called bulk metallic glass (BMG) alloys have extremely low critical cooling rates and can be used in AM. Recent studies on AM from Zr-based BMGs by selective laser me…
We study a colloidal suspension confined between two quasi-parallel walls as a model system for glass transitions in confined geometries. The suspension is a mixture of two particle sizes to prevent wall-induced crystallization. We use confocal microscopy to directly observe the motion of colloidal particles. This motion is slower in confinement, thus producing glassy behavior in a sample which is a liquid in an unconfined geometry. For higher volume fraction samples (closer to the glass transition), the onset of confinement effects occurs at larger length scales.
December 1991 legislation in France has spurred research on enhanced separation and conditioning or transmutation of long-lived radionuclides from high level radioactive wastes (HLW). In this field, we have studied zirconolite-based glass-ceramics in which the crystalline phase (zirconolite: CaZrTi2O7) aimed to preferentially incorporate minor actinides is embedded in a glassy calcium aluminosilicate matrix. At the laboratory scale, the crystallization of the parent glass is carried out thanks to a two-step thermal treatment: a nucleation stage followed by a growth stage. This paper presents t…
There are at least three fundamental states of matter, depending upon temperature and pressure: gas, liquid, and solid (crystal). These states are separated by first-order phase transitions between them. In both gas and liquid phases the complete translational and rotational symmetry exist, whereas in a solid phase both symmetries are broken. In intermediate phases between liquid and solid, which include liquid crystal and plastic crystal phases, only one of the two symmetries is preserved. Among the fundamental states of matter, the liquid state is most poorly understood. We argue that it is …
Despite two decades of studies, the formation of metallic glasses, very promising systems for industrial applications, still remains mostly unexplained. This lack of knowledge hinders the search for new systems, still performed with combinatorial trial and error. In the past, it was speculated that some sort of "confusion" during crystallization could play a key role during their formation. In this article, we propose a heuristic descriptor quantifying such confusion. It is based on the "thermodynamic density of competing crystalline states", parameterized from high-throughput ab-initio calcul…
Development of reliable interatomic potentials is crucial for theoretical studies of relationship between chemical composition, structure and observable properties in glass-forming metallic alloys. Due to ambiguity of potential parametrization procedure, some crucial properties of the system, such as crystallization stability or symmetry of the ground state crystal phase, may not be correctly reproduced in computer simulations. Here we address this issue for ${\rm Cu_{64.5}Zr_{35.5}}$ alloy described by two modifications of embedded atom model potential as well as by \textit{ab initio} molecul…
By combining atomistic simulations with a detailed analysis of individual atomic hops, we show that the diffusion of carbon in a binary Fe-C glass exhibits strong (anti-)correlations and is largely determined by the local environment. Higher local carbon concentrations lead to slower atomic mobility. Our results help explain the increasing stability of Fe-C (and other similar metal-metalloid glasses) against crystallization with increasing carbon concentration.
We report observation of crystallization of the glass-forming binary Lennard-Jones liquid first used by Wahnström [G. Wahnström, Phys. Rev. A 44, 3752 (1991)]. Molecular dynamics simulations of the metastable liquid on a timescale of microseconds were performed. The liquid crystallized spontaneously. The crystal structure was identified as MgZn_2. Formation of transient crystallites is observed in the liquid. The crystallization is investigate at different temperatures and compositions. At high temperature the rate of crystallite formation is the limiting factor, while at low temperature the l…
Crystal nucleation and growth processes induced by an externally applied shear strain in a model metallic glass are studied by means of nonequilibrium molecular dynamics simulations, in a range of temperatures. We observe that the nucleation-growth process takes place after a transient, induction regime. The critical cluster size and the lag-time associated with this induction period are determined from a mean first-passage time analysis. The laws that describe the cluster growth process are studied as a function of temperature and strain rate. A theoretical model for crystallization kinetics …
Microstructure-specific mechanisms define multistage relaxation dynamics in a metallic model-glass
Federal Institute of Materials Research and Testing (BAM)（联邦材料研究和测试研究所）；Technical University of Munich（慕尼黑工业大学）；University of Illinois at Urbana-Champaign（伊利诺伊大学厄巴纳-香槟分校）
This work concerns glasses belonging to SiO2-Al2O3-CaO-ZrO2-TiO2-Nd2O3 system that lead to zirconolite crystallization in their bulk after nucleation + crystal growth thermal treatments and that could find application as nuclear waste form. The understanding of crystallization processes in glasses implied to investigate their structure. The environment around Ti, Zr (nucleating agents) and Nd was characterized for various Nd2O3 loadings. Electron spin resonance study of the small amount of Ti3+ occurring in glasses enabled to identify two types of sites for titanium. EXAFS showed that Zr occup…
Primary crystallization in high Al-content metallic glasses is driven by nanometer-diameter regions with internal structure similar to fcc Al. Comparison of fluctuation electron microscopy (FEM) data to FEM simulations of fcc Al clusters dispersed in a dense-random packed matrix is used to extract the diameter and volume fraction of the ordered regions in a Al88Y7Fe5 base glass and in glasses with 1 at.% Cu substituted for Y or Al. The size and density of nanocrystals were measured as a function of isothermal annealing time for the same alloys. The volume fraction of crystalline material grows…
Colloidal Janus spheres in water (one hemisphere attractive and the other repulsive) assemble into two-dimensional hexagonal crystals with orientational order controlled by anisotropic interactions. We exploit the decoupled translational and rotational order to quantify the orientational dynamics. Via imaging experiments and Monte Carlo simulations we demonstrate that the correlations in the orientation of individual Janus spheres exhibit glasslike dynamics that can be controlled via the ionic strength. Thus, these colloidal building blocks provide a particularly suitable model glass system fo…
Using a modified Lennard-Jones model for anisotropic particles, we present results of molecular dynamics simulation in two dimensions. In one-component systems, we find crystallization, a Berezinskii-Kosterlitz-Thouless phase, and a structural phase transition, as the temperatures is lowered. In the lowest temperature range, the crystal is composed of three martensitic variants on a hexagonal lattice, exhibiting the shape memory effect. With addition of larger spherical particles (impurities), these domains are finely divided, yielding glass with slow time evolution. With increasing the impuri…
The process of homogeneous crystal nucleation has been considered in a model liquid, where the interparticle interaction is described by a short-range spherical oscillatory potential. Mechanisms of initiating structural ordering in the liquid at various supercooling levels, including those corresponding to an amorphous state, have been determined. The sizes and shapes of formed crystal grains have been estimated statistically. The results indicate that the mechanisms of nucleation occurs throughout the entire considered temperature range. The crystallization of the system at low supercooling l…
We study the influence of the liquid-vapor surface on the crystallization kinetics of supercooled metal alloys. While a good glass former, $\rm{Cu}_{50}\rm{Zr}_{50}$, shows no evidence of surface enhancement of crystallization, $\rm{Ni}_{50}\rm{Al}_{50}$ exhibits an increased rate of crystallization due to heterogeneous nucleation at the free liquid surface. The difference in the compositional fluctuations at the interface is proposed as the explanation of the distinction between the two alloys. Specifically, we observe compositional ordering at the surface of $\rm{Ni}_{50}\rm{Al}_{50}$ while …
