Crystallization Mechanism Research Articles

Kinetic analysis of the crystallization of Y2O3 and La2O3 doped Li2O-Al2O3-SiO2 glass.

Li2O-Al2O3-SiO2 (LAS) glass ceramics have a low coefficient of thermal expansion, high mechanical strength, and excellent chemical stability. With advancements in glass ceramics, researchers have explored using LAS glass ceramics with transition metal doping and rare earth doping. Most previous studies have studied the impact of rare earth element doping on crystallization primarily in the context of conventional nucleating agents present in glass. In this study, we aimed to investigate the impact of Y2O3 and La2O3 on LAS glasses in the presence of undoped nucleating agents. The crystallization mechanism of La2O3 and Y2O3 doped LAS glass ceramics was studied using differential scanning calorimetry. The crystallization kinetics of the glasses were analyzed using model-free and modeling methods. Moreover, the activation energy of crystallization and the indices of crystallization and growth of glass ceramics were calculated, and the crystalline phase and microstructure of the samples were characterized. All three fractions of the LAS glass showed consistent crystallization under different calculation methods. The glass doped with La2O3 and Y2O3 exhibited two- or three-dimensional growth during crystallization, promoting crystallization in the LAS glass. The Y3La0 sample demonstrated the most favorable crystallization effect. In the presence of an undoped nucleating agent, rare earth elements can enhance glass crystallization; this new idea can be utilized for the development of new materials.

Efficient and economical removal and recovery of phosphorus via a novel dual-electrode electrochemically induced crystallization process: Performance and crystallization mechanisms

Electrochemically induced crystallization is a promising method for removing and recovering P from wastewater but may be hindered by intrinsic limitations, e.g., high energy consumption and cost. To overcome such limitations, a dual-electrode electrochemically induced crystallization process (DEIC) was proposed using an electrochemical reactor equipped with an iron anode and a stainless-steel cathode. Results showed that > 95% P removal was achieved in 20 hours at the experimental conditions of current density = 0.2 mA/cm2, pH = 6.5, Ca2+ = 5.4 mM, and P concentration = 6.5 mM. The specific energy consumption was calculated as 0.82 kWh/kg P, which is much lower than the reported results (7 – 65 kWh/kg P). According to the XRD and SEM-EDS analysis, P removal was achieved in the form of vivianite (Fe3(PO4)2.8 H2O) and CaP crystallization, induced by the releases of Fe2+ and OH– at the anode and cathode, respectively. Vivianite was found to be deposited at the anode with high purity and a regular plane structure. The DFT calculation confirmed that the control of vivianite growth in a plane shape is thermodynamically feasible. Lastly, the economic analysis showed that the operational cost of DEIC (1.07 USD/kg P) was lower than that of conventional chemical precipitation (1.3 – 1.8 USD/kg P), suggesting that the DEIC process could be a viable method to achieve P removal and recovery.

Nucleation and grain growth in low-temperature rapid solid-phase crystallization of hydrogen-doped indium oxide

Nucleation and grain growth are discussed as a means of clarifying the mechanism of the rapid solid-phase crystallization (SPC) process of H2-doped amorphous indium oxide (InO x :H) films. H2-doping in InO x :H films reduced nucleation density at 250 °C from 4.1 to 1.1 μm−2, resulting in an increase in grain size and Hall mobility of the polycrystalline (poly)-InO x :H films. Lateral growth rate from the nucleus was estimated to be 220 nm min−1 for the InO x :H film at 250 °C. Thus, an amorphous InO x :H film could be converted to a poly-InO x :H film within 3 min owing to a fast lateral growth rate from the nucleus. Almost the same grain size, Hall mobility, and carrier density could be obtained from the poly-InO x :H films after annealing at 250 °C for only 3 min irrespective of the ramp rate. The results demonstrated the wide range of the processing window for SPC for poly-InO x :H films.

Unique Crystallization Characteristics of Pickering High Internal Phase Emulsion Templated Porous Constructs.

To study the crystallization behavior of polymeric chains under the influence of porosity, the thermal properties of various nonporous and porous poly(ε-caprolactone) (PCL) based constructs were investigated. Porous cross-linked PCL nanocomposite constructs were fabricated utilizing in situ polymerization of CL-based surfactant-free Pickering high internal phase emulsions (HIPEs), stabilized using modified fumed silica nanoparticles (mSiNP) at a minimal concentration of 0.6 wt %. The corresponding nanocomposite constructs exhibited polyhedral pore morphology with significant pore roughness due to the presence of mSiNP. DSC thermograms of nonporous constructs illustrated diminished crystallization temperature and kinetics upon cross-linking and inclusion of mSiNP which confirmed suppressed mobility of polymer chains. Further introduction of porosity led to substantial supercooling, resulting in crystallization temperatures as low as -24 °C. Changes in the crystal structure of various nonporous and porous constructs were also studied using XRD. The crystallization behavior of porous constructs was finally evaluated using Jeziorny, Ozawa, and Mo theories under nonisothermal conditions. Significant deviation from the theoretical model, as observed in the case of porous constructs, implied a complex crystallization mechanism that eventually was not only controlled by the chain immobility due to cross-linking but also heterogeneity present in the wall thickness of the constructs. The unique melting-crystallization phenomenon observed in such constructs may further be expanded to other systems of high heat capacity for utilization as energy storage materials.

Effect of La, Zr Doping on the Structural and Electrical Conduction Behaviour of BiFeO<sub>3</sub>-BaTiO<sub>3</sub> Ceramics

<p>This study presents a comprehensive investigation of the crystal structure and DC conduction mechanism of [(Ba<sub>0.7-x</sub> La<sub>x</sub>) Bi<sub>0.3</sub>][(Ti<sub>0.5</sub> Zr<sub>0.2</sub>) Fe<sub>0.3</sub>]O<sub>3</sub> with x = 0.00, 0.01, 0.03, 0.05 employing X-ray diffraction (XRD) and electrical conductivity measurements. Various compositions were synthesized through the solid-state ceramic route. XRD was used to investigate phase formation. Analysis of XRD data suggested a structural transition from cubic to tetragonal for x ≥ 0.01. The average crystallite size first increases for x = 0.01 and then decreases for x ≥ 0.03. The temperature-dependent electrical conductivity measurements were investigated over a wide temperature range which revealed distinct conductivity mechanisms governing the material's transport properties. The activation energy (E<sub>a</sub>) has been estimated from temperature-dependent DC conductivity. Overall, this study provides valuable insights into the correlation between crystal structure and electrical properties in [(Ba<sub>0.7-x</sub> La<sub>x</sub>) Bi<sub>0.3</sub>][(Ti<sub>0.5</sub> Zr<sub>0.2</sub>) Fe<sub>0.3</sub>]O<sub>3</sub>, offering significant implications for its potential applications in electronic and optoelectronic devices requiring tailored conductivity characteristics.</p>

Effect of kaolin calcined temperature on the preparation and crystallization mechanism of SAPO-34 molecular sieve for methanol-to-olefins performance

SAPO-34 molecular sieves synthesized using calcined kaolin as partial raw material under three-stage of high-low-high temperature hydrothermal condition are explored systematically. Especially, the effect of kaolin calcination temperature on the crystallization mechanism of SAPO-34 and the methanol to olefin performance are investigated thoroughly. It is found that the sample (SP-500) synthesized by using kaolin calcined at 500 °C (MK-500) demonstrates clean cubic structure, large specific surface area and mild acidity, providing the initially activated Si and Al source for the synthesis of SAPO-34 molecular sieve due to the well scattered structure of MK-500. From the crystallization mechanism consideration, it can be proposed that the SAPO-34 molecular sieves will be controlled by the low degree of Si aggregation in metakaolin and quantity of Si (3Al,1Si) species. As a result, SP-500 displays excellent catalytic lifetime during methanol to olefin reaction for its special Si coordination environment, showing the highest stable light olefin yield of 80.6 % and a methanol conversion above 90 % for more than 720 min. In contrast, SP-800 sample with the most strong acid sites is only 390 min, even if showcasing the highest selectivity of light olefins (84.5%).

Criticality Controlling Mechanisms in Nematic Liquid Crystals

We theoretically study the generic mechanisms that could establish critical behavior in nematic liquid crystals (NLCs). The corresponding free energy density terms should exhibit linear coupling with the nematic order parameter and, via this coupling, enhance the nematic order. We consider both temperature- and pressure-driven, order–disorder phase transitions. We derive a scaled effective free energy expression that describes how qualitatively different mechanisms enforce critical behavior. Our main focus is on the impact of nanoparticles (NPs) in homogeneous NP-NLC mixtures. We illustrate that in the case of pressure-driven phase changes, lower concentrations are needed to impose critical point conditions in comparison with pure temperature variations.

Unravelling the amorphous structure and crystallization mechanism of GeTe phase change memory materials

The reversible phase transitions in phase-change memory devices can switch on the order of nanoseconds, suggesting a close structural resemblance between the amorphous and crystalline phases. Despite this, the link between crystalline and amorphous tellurides is not fully understood nor quantified. Here we use in-situ high-temperature x-ray absorption spectroscopy (XAS) and theoretical calculations to quantify the amorphous structure of bulk and nanoscale GeTe. Based on XAS experiments, we develop a theoretical model of the amorphous GeTe structure, consisting of a disordered fcc-type Te sublattice and randomly arranged chains of Ge atoms in a tetrahedral coordination. Strikingly, our intuitive and scalable model provides an accurate description of the structural dynamics in phase-change memory materials, observed experimentally. Specifically, we present a detailed crystallization mechanism through the formation of an intermediate, partially stable ‘ideal glass’ state and demonstrate differences between bulk and nanoscale GeTe leading to size-dependent crystallization temperature.

Spherical Crystallization Based on Liquid-Liquid Phase Separation in a Reverse Antisolvent Crystallization Process

Vanillin crystals undergo needle-like morphology that results in poor flowability, crystal breakage, and low packing density. The spherical crystallization technology can produce particles with improved flowability and stability. A reverse antisolvent crystallization based on liquid-liquid phase separation is proposed in this work to produce vanillin spherical agglomerates. Hansen Solubility Parameters are applied to explain the liquid-liquid phase separation (LLPS) phenomenon. The Pixact Crystallization Monitoring system is applied to in-situ monitor the whole process. A six-step spherical crystallization mechanism is revealed based on the recorded photos, including the generation of oil droplets, nucleation inside oil droplets, the coalescence and split of oil droplets, crystal growth and agglomeration, breakage of oil droplets, and attrition of agglomerates. Different working conditions are tested to explore the best operation parameters and a frequency-conversion stirring strategy is proposed to improve the production of spherical crystals.

Nano-positive up negative down in binary oxide ferroelectrics

Ferroelectric HfO2 and ZrO2-based materials are promising candidates for next-generation ferroelectric devices, but their characterization is challenging due to complex factors such as crystal phases, degradation mechanisms, and local inhomogeneities. In this work, we propose a novel nanosized positive-up-negative-down (PUND) method to assess the ferroelectric response of doped-HfO2. This method is based on actual current probing and is immune to most electrostatic artifacts that plague other electrical atomic force microscopy (AFM) techniques. We demonstrate the PUND method’s ability to induce ferroelectric switching in Si-doped HfO2 and investigate the distinctive PUND response obtained for individual grains. We also extract the polarization charge based on a direct estimate of the tip–sample contact area. The proposed PUND method is a significant innovation as it is a method to combine the high spatial resolution of AFM with the immunity to electrostatic artifacts of current probing. This makes it a powerful tool for studying ferroelectric materials at the nanoscale, where local inhomogeneities and other effects can have a significant impact on their behavior. The PUND method is also notable for its ability to extract polarization charge based on a direct estimate of the tip–sample contact area. This is a significant improvement over previous methods, which often relied on indirect or approximate estimates of the contact area. Overall, the PUND method is a novel and innovative technique that offers significant advantages for the characterization of ferroelectric materials at the nanoscale. It is expected to have a major impact on the research and development of next-generation ferroelectric devices.

Divergence among Local Structure, Dynamics, and Nucleation Outcome in Heterogeneous Nucleation of Close-Packed Crystals.

Heterogeneous crystal nucleation is the dominant mechanism of crystallization in most systems, yet its underlying physics remains an enigma. While emergent interfacial crystalline order precedes heterogeneous nucleation, its importance in the nucleation mechanism is unclear. Here, we use path sampling simulations of two model systems to demonstrate that crystalline order in its traditional sense is not predictive of the outcome of the heterogeneous nucleation of close-packed crystals. Consequently, structure-based collective variables (CVs) that reliably describe homogeneous nucleation can be poor descriptors of heterogeneous nucleation. This divergence between structure and nucleation outcome is accompanied by an intriguing dynamical anomaly, wherein low-coordinated crystalline particles outpace their liquid-like counterparts. We use committor analysis, high-throughput screening, and machine learning to devise CV optimization strategies and present suitable structural heuristics within the metastable fluid for CV prescreening. Employing such optimized CVs is pivotal for properly characterizing the mechanism of heterogeneous nucleation in metallic and colloidal systems.

The Crystallization and Melting Behavior of Neodymium-Based Butadiene Rubber Blends.

This study investigates the influence of poly(butadiene-isoprene) copolymer rubber (BIR) and TDAE oil on the crystallization and melting behavior of neodymium-based butadiene rubber (Nd-BR). The study demonstrates that the melting points of Nd-BR and its blends decrease with lower crystallization temperatures. Below the critical crystallization temperature (Tc,c), the melting behavior shows dual peaks in distinct temperature ranges, which are attributed to different spherulitic sizes. The addition of BIR or TDAE oil lowers the Tc,c, with TDAE oil exerting a more substantial effect. These diluents mainly influence the nucleation temperature and crystallinity level of Nd-BR while having a minimal effect on the crystallization mechanism. A master curve, which overlaps for various samples, is developed by correlating the peak melting temperature (Tm,peak) with the Tc. This curve facilitates a quantitative assessment of the effects of BIR and TDAE oil on Nd-BR, highlighting the greater influence of TDAE oil on the crystalline structure compared with BIR at equivalent mass fractions. By applying the Lorentz equation and multi-peak fitting, a relationship between the melting points and crystallization temperatures is established, enabling the calculation of the equilibrium melting points (Tm0) for different samples. The findings show a reduction in the Tm0 due to the diluents; specifically, the Tm0 is approximately 0 °C for pure Nd-BR, and it decreases to -4.579 °C and -6.579 °C for samples with 50 PHR TDAE oil and 60 wt.% BIR, respectively.

Insight of Synthesis of Single Crystal Ni‐Rich LiNi1−x−yCoxMnyO2 Cathodes

AbstractSingle‐crystal Ni‐rich LiNi1−x−yCoxMnyO2 (NCM) cathodes have garnered widespread attention in the lithium‐ion battery community due to their unique advantages in mechanical performance and their ability to minimize interfacial electrochemical side reactions. The synthesis of single‐crystal materials with monodisperse and appropriate size, minimal lattice defects, and highly ordered structures is the key for high‐performance batteries. However, achieving this goal poses challenges due to the lack of in‐depth understanding regarding specific experimental parameters and the solid reaction mechanism during the synthesis process. In this review, the aim is to provide an in‐depth analysis of the critical process parameters involved in the synthesis and their impact on crystal morphology, structure, and electrochemical performance. Consequently, the first section focuses on the effect of the precursor morphology, lithium salt, atmosphere, and sintering procedure. In the second section, the study delves into an in‐depth discussion of the solid reaction and crystal growth mechanism. Lastly, it is concluded by highlighting the prospects and challenges associated with the synthesis and application of single‐crystal Ni‐rich NCM cathodes.

Advanced isoconversional kinetic analysis: Insight in mechanisms and simulations. Successes and future

Various examples of application of advanced isoconversional kinetic analysis are discussed. The paper focuses on polymerization and crystallization mechanisms, protein denaturation and simulations in a model-free way under different temperature programs. It is shown how isoconversional kinetic analysis was developed in the recent years to gain meaningful kinetic information on changes in rate-limiting steps and was applied to multi-step processes. The complementary of the information obtained by estimating pre-exponential factors, rate constants and mathematical function that describes the reaction mechanism, in addition to the usual effective activation energy dependency, is highlighted. In addition, combination of model-free and model-based methods can be used for the elucidation of multi-step kinetics.

Revealing the Effect of the Molecular Weight Distribution on the Chain Diffusion and Crystallization Process under a Branched Trimodal Polyethylene System.

With the increasing demand for high-end materials, trimodal polyethylene (PE) has become a research hotspot in recent years due to its superior performance compared with bimodal PE. By means of molecular dynamics (MD) simulations, we aim to expound the effect of the molecular weight distribution (MWD) on the mechanism of nucleation and crystallization of trimodal PE. The crystallization rate is faster when short-chain branching is distributed on a single backbone compared to that on two backbones. In addition, as the content of high molecular weight backbone decreases, the time required for nucleation decreases, but the crystallization rate slows down. This is because low molecular weight backbones undergo intra-chain nucleation and crystallize earlier due to the high diffusion capacity, which leads to entanglement that prevents the movement of medium or high molecular weight backbones. Furthermore, crystallized short backbones hinder the movement and crystallization of other backbones. What is more, a small increase in the high molecular weight branched backbone of trimodal PE can make the crystallinity greater than that of bimodal PE, but when the content of high molecular weight backbone is too high, the crystallinity decreases instead, because the contribution of short and medium backbones to high crystallinity is greater than that of long backbones.

Microscopic mechanisms of pressure-induced amorphous-amorphous transitions and crystallisation in silicon

Some low-coordination materials, including water, silica, and silicon, exhibit polyamorphism, having multiple amorphous forms. However, the microscopic mechanism and kinetic pathway of amorphous-amorphous transition (AAT) remain largely unknown. Here, we use a state-of-the-art machine-learning potential and local structural analysis to investigate the microscopic kinetics of AAT in silicon after a rapid pressure change. We find that the transition from low-density-amorphous (LDA) to high-density-amorphous (HDA) occurs through nucleation and growth, resulting in non-spherical interfaces that underscore the mechanical nature of AAT. In contrast, the reverse transition occurs through spinodal decomposition. Further pressurisation transforms LDA into very-high-density amorphous (VHDA), with HDA serving as an intermediate state. Notably, the final amorphous states are inherently unstable, transitioning into crystals. Our findings demonstrate that AAT and crystallisation are driven by joint thermodynamic and mechanical instabilities, assisted by preordering, occurring without diffusion. This unique mechanical and diffusion-less nature distinguishes AAT from liquid-liquid transitions.

Tuning Reactive Crystallization Pathways for Integrated CO2 Capture, Conversion, and Storage via Mineralization.

ConspectusAchieving carbon neutrality requires realizing scalable advances in energy- and material-efficient pathways to capture, convert, store, and remove anthropogenic CO2 emission in air and flue gas while cogenerating multiple high-value products. To this end, earth-abundant Ca- and Mg-bearing alkaline resources can be harnessed to cogenerate Ca- and Mg-hydroxide, silica, H2, O2, and a leachate bearing high-value metals in an electrochemical approach with the in situ generation of a pH gradient, which is a significant departure from existing pH-swing-based approaches. To accelerate CO2 capture and mineralization, CO2 in dilute sources is captured using solvents to produce CO2-loaded solvents. CO2-loaded solvents are reacted Ca- and Mg-bearing hydroxides to produce Ca- and Mg-carbonates while regenerating the solvents. These carbonates can be used as a temporary or permanent store of CO2 emissions. When carbonates are used as a temporary store of CO2 emissions, electrochemical sorbent regeneration pathways can be harnessed to produce high-purity CO2 while regenerating Ca- and Mg-hydroxide and coproducing H2 and O2. Figure 1 is a schematic representation of this integrated approach.Tuning the molecular-scale and nanoscale interactions underlying these reactive crystallization mechanisms for carbon transformations is crucial for achieving kinetic, chemical, and morphological controls over these pathways. To this end, the feasibility of (i) crystallizing Ca- and Mg-hydroxide during the electrochemical desilication of earth-abundant alkaline industrial residues, (ii) accelerating the conversion of Ca- and Mg-carbonates for temporary or permanent carbon storage by harnessing regenerable solvents, and (iii) regenerating Ca- and Mg-hydroxide while coproducing high-purity CO2, O2, and H2 electrochemically is established.Evidence of the fractionation of heterogeneous slag to coproduce silica, Ca- and Mg-hydroxide, and a leachate bearing metals during electrochemical desilication provides the basis for further tuning the physicochemical parameters to improve the energy and material efficiency of these pathways. To address the slow kinetics of CO2 capture and mineralization starting from ultradilute emissions, reactive capture pathways that harness solvents such as Na-glycinate are shown to be effective. The extents of carbon mineralization of Ca(OH)2 and Mg(OH)2 are 97% and 78% using CO2-loaded Na-glycinate upon reacting for 3 h at 90 °C. During the regeneration of Ca- and Mg-hydroxide and high-purity CO2 from carbonate sources, charge efficiencies of as high as 95% were observed for the dissolution of MgCO3 and CaCO3 while stirring at 100 rpm. Higher yields of Mg(OH)2 are observed compared to that for Ca(OH)2 during sorbent regeneration due to the lower solubility of Mg(OH)2. These findings provide the scientific basis for further tuning these reactive crystallization pathways for closing material and carbon cycles to advance a sustainable climate, energy, and environmental future.

Rapid identification of highly glass-forming alloys in Cu–Zr binary system by laser glazing

The high-efficient experimental identification of novel metallic glasses with high glass-forming ability (GFA) is crucial for breaking through the traditional trial-and-error approach, which is time-consuming and costly. A rapid detection method for highly glass-forming alloys using laser glazing was introduced and validated in a classic binary Cu–Zr system with well-known GFA across a wide compositional range. The vitrification degree induced by laser glazing was assessed for each selected alloy and shows a strong correlation with GFA determined by traditional rapid solidification methods. The combination of experimental kinetic analysis and theoretical finite element simulation revealed possible thermodynamic mechanisms of glass formation and crystallization in the heat-affected zone (HAZ) formed by laser glazing. The results offer insights into not only the rapid identification method of highly glass-forming alloys using laser glazing but also the mechanism of glass formation under fast heating and cooling processes, providing guidance on the construction of bulk metallic glasses through laser additive manufacturing.

Normalized characterization of the causes of discontinuous yield and crystal orientation deflection mechanism of β-Ti alloy during high-temperature deformation

To investigate the changes in grain orientation resulting from dislocation slip systems and propose a novel approach to characterizing discontinuous yield behavior during hot deformation, Ti–6V–5Al–5Mo–5Cr–3Nb–2Zr-0.2Si alloy was melted using vacuum arc furnace and subjected to hot compressed at 740, 790, 840 and 890 °C, along with strain rates (ε˙) of 0.001, 0.01, 0.1 and 0.5 s−1. The results indicate that discontinuous yield is observed at temperatures (T) of 740 or 790 °C and ε˙ of 0.1 and 0.5 s−1. Discontinuous yielding occurs at all strain rates when T is 840 and 890 °C. The presence of discontinuous yield is only observed when the power dissipation value exceeds the critical value, which in this study is 0.2657. Notably, this is the first instance in which the power dissipation value has been utilized to characterize the presence of discontinuous yield. The microstructure of the discontinuous yield reveals the activation of dislocation slip in the β grain. The dislocation slip is initially activated in the <001> oriented β grains during hot compression, followed by activation in the adjacent <101> oriented β grains. When the power dissipation exceeds the critical value, the dislocations more readily spread to the <101> oriented β grains due to higher activation energy, which is an important reason for discontinuous yield. The <101> oriented β grains gradually deflect to <2−3−1> oriented and finally rotate to <001> oriented during the subsequent compression process, as a means of reducing deformation resistance.

A microdamage model for FCC single crystals considering a mixed failure mechanism of slip and cleavage

In this study, a microdamage model is newly proposed to predict the failure process of FCC single crystals. Two micro damage mechanisms, slip and cleavage, are both involved in the model. A microscopic damage variable is first defined at the slip plane scale, and a damage coupled crystal plasticity constitutive equation in a co-rotational tensor framework is then established. A damage driving force consisting of generalized energies related to the resolved shear stress and the positive resolved normal stress is proposed to reflect the mixed failure mechanism of FCC single crystals induced by slip and cleavage. The damage evolution equation is then derived in the framework of thermodynamics. An explicit algorithm for the damage coupled crystal plasticity finite element method is given. The proposed microdamage model is utilized to predict the slip-dominant fracture behavior of a single crystal copper and the cleavage-dominant fracture behavior of a nickel-based single crystal alloy. The damage evolution process of slip planes is given and the influence mechanism is revealed. The calculated results agree well with the experimental data, which verifies the good capability of the proposed model in describing and predicting the multi failure processes of FCC metals. Finally, a 2D fracture simulation of a single crystal notched specimen under shear loading is conducted, and the effect of damage parameters on the fracture modes is also discussed.