Amorphous-crystalline Interface Research Articles

Amorphous-Crystalline Interface Induced Internal Electric Fields for Electrochromic Smart Window.

Balancing optical modulation and response time is crucial for achieving high coloration efficiency in electrochromic materials. Here, internal electric fields are introduced to titanium dioxide nanosheets by constructing abundant amorphous-crystalline interfaces, ensuring large optical modulation while reducing response time and therefore improving coloration efficiency. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) reveals the presence of numerous amorphous-crystalline phase boundaries in titanium dioxide nanosheets. Kelvin probe force microscopy (KPFM) exhibits an intense surface potential distribution, demonstrating the presence of internal electric fields. Density functional theory (DFT) calculations confirm that the amorphous-crystalline heterointerfaces can generate internal electric fields and reduce diffusion barriers of lithium ions. As a result, the amorphous-crystalline titanium dioxide nanosheets exhibit better coloration efficiency (35.1cm2C-1) than pure amorphous and crystalline titanium dioxide nanosheets.

Boron Modified Nife-MOF-74 Catalyst for Application in Advanced Anion Exchange Membrane Water Electrolyzers

Despite the promising potential of non-platinum group metal electrocatalysts for anion exchange membrane (AEM) electrolysis, their practical application remains a challenge.1 Metal–organic frameworks (MOFs) and their derivatives have gained significant attention due to their high surface area, 3D periodic porous structure, large porosities, diverse composition, and well-defined metal centers as potential OER electrocatalysts in AEM electrolysis.2 However, there is a limited research report that MOFs could be used in the membrane electrode assembly (MEA) test due to the inherent limitations, such as poor stability in water, especially under basic/acidic conditions and low electrical conductivities.3,4 To address these challenges, we present a novel approach involving the introduction of boron atoms into an aromatic carbon framework. In this study, we have successfully fabricated micro-nano flower-like bimetallic NiFe-MOF-74 doped with boron. These innovative materials exhibit exceptional catalytic activity, boasting an impressively low overpotential of 318 mV for OER at a laboratory-grade current density ranging from 10 to 100 mA/cm2. Moreover, they demonstrate rapid reaction kinetics, as evidenced by a small Tafel slope of 89 mV dec-1 in 1.0 M KOH solution. In addition, our research highlights the outstanding performance of boron-modified NiFe-MOF-74 as a robust anode material for AEM water electrolysis. This significant development paves the way for a promising electrocatalyst in the realm of anion exchange membrane water electrolysis. Our findings hold great potential for advancing the field and overcoming the existing challenges associated with non-platinum group metal electrocatalysts in AEM electrolysis.Reference:(1) Song, W.; Peng, K.; Xu, W.; Liu, X.; Zhang, H.; Liang, X.; Ye, B.; Zhang, H.; Yang, Z.; Wu, L.; Ge, X.; Xu, T. Upscaled Production of an Ultramicroporous Anion-Exchange Membrane Enables Long-Term Operation in Electrochemical Energy Devices. Nat Commun 2023, 14 (1), 2732. https://doi.org/10.1038/s41467-023-38350-7.(2) He, F.; Zheng, Q.; Yang, X.; Wang, L.; Zhao, Z.; Xu, Y.; Hu, L.; Kuang, Y.; Yang, B.; Li, Z.; Lei, L.; Qiu, M.; Lu, J.; Hou, Y. Spin-State Modulation on Metal–Organic Frameworks for Electrocatalytic Oxygen Evolution. Advanced Materials 2023, 35 (41), 2304022. https://doi.org/10.1002/adma.202304022.(3) Meena, A.; Thangavel, P.; Jeong, D. S.; Singh, A. N.; Jana, A.; Im, H.; Nguyen, D. A.; Kim, K. S. Crystalline-Amorphous Interface of Mesoporous Ni2P @ FePOxHy for Oxygen Evolution at High Current Density in Alkaline-Anion-Exchange-Membrane Water-Electrolyzer. Applied Catalysis B: Environmental 2022, 306, 121127. https://doi.org/10.1016/j.apcatb.2022.121127.(4) Zhang, B.; Zheng, Y.; Ma, T.; Yang, C.; Peng, Y.; Zhou, Z.; Zhou, M.; Li, S.; Wang, Y.; Cheng, C. Designing MOF Nanoarchitectures for Electrochemical Water Splitting. Advanced Materials 2021, 33 (17), 2006042. https://doi.org/10.1002/adma.202006042.

Predicting buckling regimes during first lithiation of a crystalline silicon cylindrical anode particle: Influence of size and charging rate

A mathematical model for buckling analysis during the first lithiation of cylindrical crystalline silicon (c-Si) anode particles is presented using the finite deformation framework. A reaction–diffusion model that incorporates a reversible alloying–dealloying reaction (ADR) captures the lithiation in the expanding amorphous zone, while an addition reaction models the dynamics of the crystalline-amorphous silicon interface. A “movable” lithium part and an “immovable” lithium part make up the full lithium. In sharp contrast to the case of amorphous silicon (a-Si), the axial force evolution in c-Si is found to show two different peaks during the initial and final stages of lithiation, respectively. These peaks form the basis of two different buckling criteria, which, in turn, are shown to be sensitively influenced by the influx of lithium and a crucial size-dependent parameter. This framework gives an insight towards investigating the buckling phenomena for lithiation with an evolving amorphous silicon zone due to the interface movement, which is still absent in the present literature. Additionally, the present model enables us to obtain a quantitative and mechanistic insight into and capture the previous experimental observation that the mechanical stability of a cylindrical silicon particle may be improved by maintaining a crystalline silicon core inside the amorphous shell through controlled first lithiation. It is shown that such a crystalline-amorphous core–shell structure can be advantageous to more complicated designs involving carbon fiber as the core. It is thus hoped that this model will contribute towards improving the theoretical underpinnings of an improved design of mechanically robust electrodes for next-generation batteries.

Rational design of multi-component Fe(OH)3/Ni-NiO heterostructures bifunctional catalyst for electrochemical water splitting

Exploring economic-efficient bifunctional catalysts is critical for the production of green hydrogen through water splitting. Herein, we fabricate a novel hybrid catalyst with three-phase heterojunction (Fe(OH)3/Ni-NiO) via a simple electrodeposition and chemical precipitation method. Benefiting from the desirable amorphous-crystal interfaces, the electronic structure of Ni, NiO and Fe(OH)3 is regulated, which will optimize the adsorption of H intermediates (H*) and also reduce the kinetic barrier for the hydrogen evolution reaction (HER). The optimal Fe(OH)3–3/Ni-NiO/CC shows superior bifunctional activity with low overpotentials of 66 mV for HER and 220 mV for OER at 10 mA cm−2 in alkaline solution, respectively, as well as remarkable durability over a period of 40 h. Besides, Fe(OH)3–3/Ni-NiO/CC requires 1.52 and 1.72 V to deliver 10 and 100 mA cm−2 and shows no obvious increase in current within 40 h toward overall water splitting. Experimental and theoretical results show that the HER process is promoted by the synergistic effect of electronic redistribution between Ni, NiO and Fe(OH)3 due to the construction of three phase crystalline-amorphous heterogeneous interface. Meanwhile, Fe(OH)3 and NiO appeared reconstruction, transforming into FeOOH and NiOOH during OER process, respectively. This work offers a simple synthesis method for designing bifunctional catalysts for water splitting.

Narrow Bandgap Schottky Heterojunction Sonosensitizer with High Electron-Hole Separation Boosted Sonodynamic Therapy in Bladder Cancer.

Sonodynamic therapy (SDT) is applied to bladder cancer (BC) given its advantages of high depth of tissue penetration and nontoxicity due to the unique anatomical location of the bladder near the abdominal surface. However, low electron-hole separation efficiency and wide bandgap of sonosensitizers limit the effectiveness of SDT. This study aims to develop a TiO2-Ru-PEG Schottky heterojunction sonosensitizer with high electron-hole separation and narrow bandgap for SDT in BC. Density functional theory (DFT) calculations and experiments collectively demonstrate that the bandgap of TiO2-Ru-PEG is reduced due to the Schottky heterojunction with the characteristic of crystalline-amorphous interface formed by the deposition of ruthenium (Ru) within the shell layer of TiO2. Thanks to the enhancement of oxygen adsorption and the efficient separation of electron-hole pairs, TiO2-Ru-PEG promotes the generation of reactive oxygen species (ROS) under ultrasound (US) irradiation, resulting in cell cycle arrest and apoptosis of bladder tumor cells. The in vivo results prove that TiO2-Ru-PEG boosted the subcutaneous and orthotopic bladder tumor models while exhibiting good safety. This study adopts the ruthenium complex for optimizing sonosensitizers, contributing to the progress of SDT improvement strategies and presenting a paradigm for BC therapy.

Hierarchical CoWO4/NixFeyS microspheres bearing crystalline-amorphous interface as a multifunctional platform for outperformed water splitting and sensitive hydrazine sensing

Highly efficient and multifunctional electrocatalysts are of high value in energy transformation and electrochemical sensing. Herein, hierarchically architectured cobalt tungstate/nickel iron sulfide (CoWO4/NixFeyS) microspheres with a crystalline-amorphous interface have been prepared on bimetallic substrate of nickel–iron foam (NIF) by a two-step hydrothermal method. Electrochemical characterization shows that CoWO4/NixFeyS microspheres can boost the electrocatalytic activity effectively through the synergistic effect on the crystalline-amorphous interface. When the CoWO4/NixFeyS is applied as the electrocatalysts for oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER), the overpotentials at a high current density of 500 mA cm−2 are only 322.8 mV and 306.5 mV, respectively. The overall water splitting device composed of CoWO4/NixFeyS/NIF couple only needs a cell voltage of 1.80 V to reach a current density of 100 mA cm−2, and 2.19 V to reach 500 mA cm−2. The CoWO4/NixFeyS/NIF can be also utilized as an effective electrochemical platform for the sensing of toxic hydrazine in a wide range from 50 μM to 17.3 mM, with a detection limit of 46.4 μM. All these results display that the CoWO4/NixFeyS/NIF can be a high-performance multifunctional material for energy transformation and environmental pollutant monitoring.

Amorphous-crystalline interface coupling induced highly active ultrathin NiFe oxy-hydroxide design towards accelerated alkaline oxygen evolution

Amorphous NiFe-based oxyhydroxides can provide abundant active sites for oxygen evolution reaction (OER) in alkaline water splitting, but their disordered atomic arrangement leads to severe charge accumulation and electrochemical polarization at high current density. To address this issue, a crystalline Fe2O3 supported ultrathin amorphous NiFe oxy-hydroxide amorphous-crystalline interface coupling design is proposed. In this design, the interfacial Fe3+ in Fe2O3 as a strong Lewis acid is conducive for trapping the electrons in amorphous NiFe(OH)x, reducing the surface charge accumulation, electrochemical polarization, and improves its OER performance. Meanwhile, in-situ Raman, in-situ IR and XPS analysis reveal that, the electrons transfer is accompanied with Ni2+ oxidation into the highly OER active Ni3+ species. Benefited from this design, the OER overpotentials of the resulting NiFe(OH)x/Fe2O3NAs catalyst are measured to be 111 and 233 mV at 10 and 100 mA cm−2, respectively, superior than many reported OER electrocatalysts. The anion exchange membrane water electrolyzer using NiFe(OH)x/Fe2O3NAs delivers a current density of 600 mA cm−2 at a small cell voltage of 1.75 V, and exhibits excellent stability performance in high-current–density condition. This work provides a promising alternative strategy for the development of high-performance amorphous OER catalysts.

Fe-induced crystalline-amorphous interface engineering of a NiMo-based heterostructure for enhanced water oxidation.

Engineering heterostructures with a unique surface/interface structure is one of the effective strategies to develop highly active noble-metal-free catalysts for the oxygen evolution reaction (OER), because the surface/interface of catalysts is the main site for the OER. Herein, we design a coralloid NiMo(Fe)-20 catalyst with a crystalline-amorphous interface through combining a hydrothermal method and an Fe-induced surface reconfiguration strategy. That is, after Fe3+ impregnation treatment, the Ni(OH)2-NiMoO4 pre-catalyst with a complete crystalline surface is restructured into a trimetallic heterostructure with a crystalline-amorphous interface, which facilitates mass diffusion and charge transfer during the OER. As expected, self-supported NiMo(Fe)-20 exhibits excellent electrocatalytic water oxidation performance (overpotential: η-10 = 220 mV, η-100 = 239 mV) in the alkaline electrolyte, and its electrocatalytic performance hardly changes after maintaining the current density of 50 mA cm-2 for 10 hours. Furthermore, nickel foam (NF) supported commercial Pt/C and self-supported NiMo(Fe)-20 served as the cathode and anode of the Pt/C‖NiMo(Fe)-20 electrolyzer, respectively, which exhibits a lower cell voltage (E-100 = 1.53 V) than that of the Pt/C‖RuO2 electrolyzer (E-100 = 1.58 V) assembled with noble metal-based catalysts. The enhanced electrocatalytic performance of the NiMo(Fe)-20 catalyst is mainly attributed to the synergistic effect between the crystalline-amorphous interface and the coralloid trimetallic heterostructure.

Nanoscale core-shell structure and recrystallization of swift heavy ion tracks in SrTiO3.

It is widely accepted that the interaction of swift heavy ions with many complex oxides is predominantly governed by the electronic energy loss that gives rise to nanoscale amorphous ion tracks along the penetration direction. The question of how electronic excitation and electron-phonon coupling affect the atomic system through defect production, recrystallization, and strain effects has not yet been fully clarified. To advance the knowledge of the atomic structure of ion tracks, we irradiated single crystalline SrTiO3 with 629 MeV Xe ions and performed comprehensive electron microscopy investigations complemented by molecular dynamics simulations. This study shows discontinuous ion-track formation along the ion penetration path, comprising an amorphous core and a surrounding few monolayer thick shell of strained/defective crystalline SrTiO3. Using machine-learning-aided analysis of atomic-scale images, we demonstrate the presence of 4-8% strain in the disordered region interfacing with the amorphous core in the initially formed ion tracks. Under constant exposure of the electron beam during imaging, the amorphous part of the ion tracks readily recrystallizes radially inwards from the crystalline-amorphous interface under the constant electron-beam irradiation during the imaging. Cation strain in the amorphous region is observed to be significantly recovered, while the oxygen sublattice remains strained even under the electron irradiation due to the present oxygen vacancies. The molecular dynamics simulations support this observation and suggest that local transient heating and annealing facilitate recrystallization process of the amorphous phase and drive Sr and Ti sublattices to rearrange. In contrast, the annealing of O atoms is difficult, thus leaving a remnant of oxygen vacancies and strain even after recrystallization. This work provides insights for creating and transforming novel interfaces and nanostructures for future functional applications.

Identification and thermal healing of focused ion beam-induced defects in GaN using off-axis electron holography

Thermal healing of focused ion beam-implanted defects in GaN is investigated by off-axis electron holography in TEM. The data reveal that healing starts at temperatures as low as about 250 °C. The healing processes result in an irreversible transition from defect-induced Fermi level pinning near the VB toward a midgap pinning induced by the crystalline-amorphous transition interface. Based on the measured pinning levels and the defect charge states, we identify the dominant defect type to be substitutional carbon on nitrogen sites.

Atomistic insights into the influence of Y element on the amorphization behavior of dual-phase Mg alloys

Molecular dynamics simulations are performed to investigate the effect of the interface structure, diffusion time and diffusion temperature on the diffusion behavior and amorphization mechanism of the dual-phase Mg alloys. The results indicate that there is a critical concentration of Y element in the amorphous/crystalline interface (ACI), which depends on the interface structure and temperature. And when the concentration of Y atoms in the ACI is higher than the critical concentration, the ACI will migrate towards the crystalline side, accompanied by the amorphization of the crystalline layer. In addition, it is found that the presence or absence of Y element in the amorphous layer has a significant impact on the amorphous layer thickness of the alloys. For the alloys containing Y atoms, the amorphous layer thickness increases with the increase of diffusion temperature and diffusion time.

The innate interfacial elastic strain field of a transformable B2 precipitate embedded in an amorphous matrix

When a transformable B2 precipitate is embedded in an amorphous matrix, it is often experimentally observed that the crystalline-amorphous interface not only serves as an initiation site for the martensitic transformation due to local stress concentrations, but also as an inhibitor to stabilize the transformation, the latter being attributed to the “confinement effect” exerted by the amorphous matrix, according to the Eshelby solution. These two seemingly incongruous factors are examined in this study using molecular dynamics simulations from an atomic interaction perspective. An innate strain gradient in the vicinity of the crystalline-amorphous interface is identified. The actual interface, the compressive/dilatative transition, and the interfacial maximum strain are investigated to differentiate from the conventional “interface” located within a distance of a few nanometers. Our innate interfacial elastic strain field model is applicable for the design of materials with a higher degree of martensitic transformation and controllable stress concentration, even in cryogenic environments.

Strong resistance to shear instability in multilayered metallic composites by nanoscale amorphous-BCC crystalline interfaces

Experiments have shown that high strength and high plastic stability are difficult to be simultaneously obtained in crystalline-amorphous layered composites. Here we report a complete suppression of plastic instability in a strong multilayered composite via nanoscale BCC Nb crystalline-amorphous CuNb interface architecting. Specifically, the size-dependent hardness and shear instability of the designed nanolayered composites are systematically investigated with individual layer thickness (h) ranging from 2 to 100 nm by nano/micro-indentation tests. A mechanics model is also proposed to quantify the shear instability. A non-monotonic shear instability behavior is revealed with decreasing h. When h > 40 nm, a cutting-like shear banding prevails in the composites and the shear instability reduces with decreasing h. Finally, a homogeneous plastic deformation without shear banding is achieved at h of 40 nm. For h < 40 nm, a kinking-like shear banding occurs in the composites and the shear instability increases with reducing h. Further theoretical analysis reveals a critical layer thickness for activating homogeneous deformation in the composites, i.e., 45 nm, above and below which the shear deformation would be dominated by cutting-like and kinking-like shear banding, respectively. The cutting-like shear banding is attributed to the propagation of the mature shear band formed in the amorphous phase that penetrates the crystalline layer. The homogeneous plastic deformation can be ascribed to the activation of the confined layer slip mechanism in the crystalline layer and the non-clustered shear transformation zones initiated in the amorphous layer. The kinking-like shear banding below 40 nm may originate from the cooperative kinking of the constituent layers with decreasing h. The potential advantage of the ductile BCC metals over FCC ones for suppression of shear instability in crystalline-amorphous composites is discussed based on the unique dislocation activities in nanoscale BCC crystals (e.g., self-multiplication and significant cross-slipping mechanisms). The present study sheds some light on designing strong and ductile crystalline-amorphous composites by selecting an appropriate BCC crystalline phase and an optimal interface spacing to eliminate plastic instability.

Indentation Depth-Dependent Hardness of Metal-Organic Framework Crystals: The Effect of Local Amorphization Induced by Indentation.

The hardness of metal-organic frameworks (MOFs) is an important mechanical property metric measuring their resistance to the permanent plastic deformation. The hardness of most MOFs measured from nanoindentation experiments usually exhibits the similar unique indentation depth dependence feature, the mechanism of which still remains unclear. In order to explain the effect of the indentation depth on the hardness of MOFs, we conducted nanoindentation simulations on HKUST-1 by using reactive molecular dynamics simulations. Our simulations reveal that the HKUST-1 material near the indenter can transform from the parent crystalline phase to a new amorphous phase due to the high pressure generated, while its counterpart far from the indenter remains in the crystalline phase. By considering the crystalline-amorphous interface in the energy analysis of MOFs, we derived an analytical expression of the hardness at different indentation depths. It is found that the interface effect can greatly increase the hardness of MOFs, as observed in nanoindentation simulations. Moreover, the proposed analytical expression can well explain the indentation depth-dependent hardness of many MOF crystals measured in nanoindentation experiments. Overall, this work can provide a better understanding of the indentation depth dependence of the hardness of MOFs.

P vacancies at the crystalline-amorphous interface of NiFe(OH)x/NiPx/NF enhance the catalytic activity of the oxygen evolution reaction

Efficient electrocatalysts are crucial for overcoming the sluggish kinetics of the oxygen-evolution reaction (OER) and facilitating the advancement of energy storage technologies such as metal-air batteries and hydrogen production through water electrolysis. This study proposes a synergistic approach combining amorphization and interfacial engineering to improve OER performance by fabricating heterojunctions between crystalline NiFe(OH)x and amorphous NiPx. The formation of a strongly coupled crystalline-amorphous heterojunction enables optimization of the electronic structure at the catalytic site and accelerates charge transfer at the interface, thereby improving the reaction kinetics. Notably, we investigate the dynamic adsorption behavior of PO43− during the OER process by introducing Na3PO4 into the electrolyte, revealing that P vacancies serve as active sites in promoting OER activity. Lastly, electrochemical measurements demonstrate that NiFe(OH)x/NiPx/NF exhibits a low overpotential of 220 mV at 10 mA cm−2 and Tafel slope of 35 mV·dec−1, surpassing the performance of laboratory-prepared noble metal catalysts and most reported NiFe-based electrocatalysts.

Modulating electronic structure and sulfur p-band center by anchoring amorphous Ni@NiSx on crystalline CdS for expediting photocatalytic H2 evolution

Photocatalytic water splitting is a prospective approach to address the energy and environmental challenges. Herein, an amorphous Ni@NiSx cocatalyst has been fabricated and simultaneously assembled onto CdS to form amorphous-crystalline Ni@NiSx-CdS photocatalyst via a partial reduction strategy. Comprehensive experiments and theoretical calculations demonstrate that the synergistic effects between the electronic coupling of amorphous-crystalline interface and the gradient work function variation induced by Ni nanocluster encapsulation achieve the deeper downshift of the S p-band center to optimize H* intermediate adsorption, enhance charge extraction ability though Schottky junction and lower H* adsorption Gibbs free energy (ΔGH*). Accordingly, the optimal Ni@NiSx-CdS photocatalyst delivers a remarkable photocatalytic H2 production rate of 78.7 mmol·g−1·h−1 with an apparent quantum efficiency (AQE) of 36.74% at 420 nm, which is approximately 18.3 and 1.5 times than that of CdS and NiSx-CdS, respectively. This work offers a novel insight into the development of amorphous nanocomposite cocatalysts for promoting solar-to-H2 energy conversion.

Electroless plating synthesis of bifunctional crystalline/amorphous Pd-NiFeB heterostructure catalysts for boosted electrocatalytic water splitting

The rational design of low-cost and high-efficient electrocatalysts to overcome the energy barrier of water splitting has aroused great attentions. The amorphous-crystalline interface heterostructure has been verified to be a promising design for modulating the charge redistribution at interface active sites for promoting water splitting, which, however, remains a challenge. Herein, a bifunctional electrocatalyst with amorphous-crystalline heterostructures is fabricated by hybridizing amorphous NiFeB alloy and crystalline Pd nanoclusters on the nickel foam (NF) via a simple electroless plating strategy. The as-synthesized Pd-NiFeB/NF catalyst exhibits excellent HER and OER performance. Moreover, the assembled Pd-NiFeB/NF//Pd-NiFeB/NF electrolytic system requires a rather low cell voltage of 1.81 V to drive the durable current density of 500 mA cm−2 for at least 100 h. Theoretical calculations reveal that the addition of Pd nanoclusters reduces the energy barriers for both HER and OER, which is due to the enhanced charge transfer and optimal adsorption of intermediates.

Atomic Diffusion Mechanism in BF2+ Implanted and Annealed n-Fz Si junction using Analytical Approach: Comparison with 2-D TCAD Process Simulation Result

Ion implantation controls the diffusion of the dopants inside the n-Fz Si bulk of the p+n Si microstrip detector. In order to understand about the diffusion mechanism of BF2 + molecules/dopants into the n-Fz Si bulk of Double Sided Silicon Strip Detector (back side) for the R3B Silicon Tracker, it is essential to know the precise information about the microscopic defect introduces inside the Si lattice of the detector for the next phase upgrade of the R3B experiment. The purpose of this paper is to present the atomic transport and electrical activation behavior of implanted BF2+ molecules/dopants at an energy of 80 KeV and a dose of 1015 ion/cm2 into the n-Fz Double Sided Silicon Strip Detector for the R3B Silicon Tracker after annealing at 400 °C - 1350 °C.The result shows the amorphous-crystalline interface position and recrystallization temperature using the results revealed from the 2-D TCAD process simulation of the Si microstrip detector.

Effect of precipitate shape and distribution on mechanical behavior of shape memory metallic glass composites by molecular dynamics method

The deformation behaviors of metallic glass composites enhanced with brick and cylindrical shape B2-CuZr precipitates were investigated by molecular dynamics method. Both specimens experience a two-stage phase transformation and triple-yielding phenomenon. The brick-shaped precipitate enhanced bulk metallic glass composite (BMGC) exhibits significantly improved strength and mildly enhanced plasticity compared to cylindrical shape inclusion reinforced BMGC. The larger aspect ratio of brick-shaped precipitate enhanced BMGC strengthens the composite by improving elastic lattice deformation along loading direction, while the enhanced plasticity is ascribed to smaller free path for mature shear bands formation. The deformation mechanism for brick-shaped BMGCs is shear band cutting through precipitates, while that for cylindrical shape precipitate reinforced BMGCs is shear band wrapping around crystalline particles. Both specimens display high strain at crystalline/amorphous interface (CAI) region and might experience interfacial stability issue.

Atomistic Construction of Silicon Nitride Ceramic Fiber Molecular Model and Investigation of Its Mechanical Properties Based on Molecular Dynamics Simulations.

Molecular simulations are currently receiving significant attention for their ability to offer a microscopic perspective that explains macroscopic phenomena. An essential aspect is the accurate characterization of molecular structural parameters and the development of realistic numerical models. This study investigates the surface morphology and elemental distribution of silicon nitride fibers through TEM and EDS, and SEM and EDS analyses. Utilizing a customized molecular dynamics approach, molecular models of amorphous and multi-interface silicon nitride fibers with complex structures were constructed. Tensile simulations were conducted to explore correlations between performance and molecular structural composition. The results demonstrate successful construction of molecular models with amorphous, amorphous-crystalline interface, and mixed crystalline structures. Mechanical property characterization reveal the following findings: (1) The nonuniform and irregular amorphous structure causes stress concentration and crack formation under applied stress. Increased density enhances material strength but leads to higher crack sensitivity. (2) Incorporating a crystalline reinforcement phase without interfacial crosslinking increases free volume and relative tensile strength, improving toughness and reducing crack susceptibility. (3) Crosslinked interfaces effectively enhance load transfer in transitional regions, strengthening the material's tensile strength, while increased density simultaneously reduces crack propagation.