Structural Defects Research Articles

Construction of spherical heterogeneous interface on ZnFe2O4@C composite nanofibers for highly efficient microwave absorption

Enriching the electromagnetic wave loss mechanism and improving the impedance matching are the keys to improve the electromagnetic wave absorption performance of carbon fibers. In this study, beaded ZnFe2O4@C absorbing composite fibers (ZFCF) with synergistic effects of magnetic loss and dielectric loss was prepared by electrospinning and heat treatment. ZnFe2O4 magnetic particles effectively improve the impedance matching and increase the loss mechanism of carbon nanofibers. The optimal ZFCF composite has excellent absorption performance, with a minimum reflection loss of -53.6 dB at 2.64 mm and the widest effective absorption bandwidth of 4.32 GHz. The excellent absorption performance is attributed to significant magnetic losses from eddy currents and magnetic resonance generated by ZnFe2O4, and strong interfacial polarization from the numerous heterogeneous interfaces. Additionally, the one-dimensional carbon nanofibers create a conductive network and structural defects that enhance conductive loss and dipole polarization effects. Moreover, the RCS of ZFCF composite was significantly reduced by -32.85 dBm2. The combination of simulation technology and material design is of great significance for the study of electromagnetic wave absorption mechanism and the rational design of electromagnetic wave absorbing coatings.

Simulated TEM imaging of a heavily irradiated metal

We recast the Howie-Whelan equations for generating simulated transmission electron microscope (TEM) images, replacing the dependence on local atomic displacements with atomic positions only. This allows rapid computation of simulated TEM images for arbitrarily complex atomistic configurations of lattice defects and dislocations in the dynamical two beam approximation directly from standard atomistic simulation output files. Large-scale massively-overlapping cascade simulations, performed with molecular dynamics, are used to generate representative high-dose nanoscale defect and dislocation microstructures in tungsten at room temperature. We then compare the simulated TEM images to experimental TEM images with similar irradiation and imaging conditions. The simulated TEM shows ‘white-dot’ damage in weak-beam dark-field imaging conditions, in agreement with our experimental observations and as expected from previous studies, and in bright-field conditions a dislocation network is observed. In this work we also compare the simulated images to the nanoscale lattice defects in the original atomic structures, and find that at high dose the white spots are not only created by small dislocation loops, but rather arise from nanoscale fluctuations in strains around curved sections of dislocation lines.

CTAB-facilitated ex-situ synthesis of chitosan-based ZnO, CuO, and ZnO/CuO nanocomposites for improved optical emission

The present investigation deals with the synthesis and characterisation of CTAB assisted pristine ZnO, CuO and ZnO/CuO nanoparticles and their corresponding chitosan based nanocomposites. The XRD and FTIR results reflect the successful formation of pristine nanoparticles as well as their chitosan nanocomposites. The X-ray photoelectron spectroscopy (XPS) study confirms the tagging of chitosan by revealing the presence of element nitrogen which is expected to be derived from the chitosan biopolymer itself. The optical investigation reveal the bandgap energy of the pristine ZnO, CuO and ZnO/CuO nanoparticles to be 3.2, 1.95 and 2.60 eV, respectively. The interaction of chitosan with the pristine samples bring in changes in the bandgap energy due to alterations in energy band structure. The photoluminescence (PL) studies also clearly indicate the improved optical and electronic property of the composites on addition of chitosan by introducing defects in the crystal structure.

Defect evolution induced by low-dose neutron irradiation and elastoplastic deformation mechanism of indium-doped GaN materials

The low-dose neutron irradiation defect evolution and nanoindentation response of indium (In)-doped gallium nitride (GaN) materials are investigated in this work, which is of great significance for improving the reliability and safety of nitride semiconductors in neutron irradiation environments, as well as for clarifying their mechanical properties. A numerical simulation approach based on molecular dynamics (MD) is utilized to construct wurtzite GaN models comprising Indium doping concentrations up to 2%. Nanoindentation simulations are performed to analyze the elastoplastic deformation mechanisms of the c-plane and m-plane In-doped GaN materials. The low-dose neutron irradiation process of In-doped GaN is further simulated, and its structural changes and defects evolution are analyzed. The indentation hardness of the c-plane GaN decreases and its Young’s modulus increases as the doping concentration increases. Increases in both the indentation hardness and Young’s modulus are seen for the m-plane GaN with the increasing doping concentration. Moreover, the doping of indium suppresses the plastic deformation both in the c-plane and m-plane GaNs. Two types of prismatic loops formation mechanisms are unraveled, i.e. the “nested shear loops pinch-off” mechanism in the m-plane perfect GaN, and the “lasso-shape shear loop pinch-off” mechanism in the m-plane In-doped GaN. When subject to low-dose neutron irradiation, In-doped GaN materials exhibit higher resistance to the generation of irradiation defects. As the doping concentration increases, the amounts of phase transformation, Frenkel pairs, and amorphization decrease.

Enhancing lithium-rich manganese cathodes: Structural optimization and defect engineering via innovative thermal treatment for improved electrochemical durability and efficiency

Lattice oxygen release, which results in progressive structural disintegration and inevitable capacity fading, poses a significant challenge to the commercialization of Li-rich Mn-based cathode materials. To mitigate voltage capacity degradation and offer a feasible manufacturing process for commercial-scale production, this study developed a cost-effective thermal processing method for a Li-rich Mn-based cathode material Li1.2Ni0.13Co0.13Mn0.54O2 based on water-spray quenching. This method refines the physical phase structure, increases the specific capacity of the material, and creates a defect-tolerant dislocation substructure in the surface lattice. Furthermore, refining the nanoparticle size suppresses the occurrence of redox side reactions and mitigates electrolyte corrosion, resulting in a material with a specific capacity of 196.7 mAh g−1 after 200 cycles at a rate of 1C. This performance markedly exceeds that achieved with the untreated material, which exhibited a capacity of 104.2 mAh g−1 under the same conditions. In contrast to the conventional surface engineering and elemental modulation techniques, this study presents a practical solution for industrial applications, facilitating cost reductions and large-scale production.

Improving the strength and maintaining good ductility of as-forged Ti6Al4V alloy by regulating the microstructural defects

Solution-aging treatment is a conventional method for enhancing the strength of titanium alloys contributed by the decomposition of metastable phases, like martensite. The traditional viewpoint suggests that the martensite transformation occurring after water quenching does not significantly contribute to the strengthening of titanium alloy and this perspective actually overlooks the high strength resulting from the high-density defects formed in the martensite microstructure due to rapid cooling. So, previous studies have not fully taken advantages of the excellent strengthening capability of martensite. This study adopted a technique which combined solid solution and incomplete aging treatment to control the decomposition behavior of martensite and as a result, the strength of the as-forged Ti-6Al-4V (TC4) alloy had been obviously improved and good ductility had been maintained. Furthermore, the changes of phase structure and microstructural defects in TC4 titanium alloy during solution and aging process have been detailly studied by XRD refinement, EBSD, and TEM. Specifically, the highest tensile strength increased by 28.8% which could reach 1224 MPa, and the elongation at fracture could still remain at 13%. The reason is as follows. The formation of martensite after water quenching led to a substantial increase in internal microstructural defects, which were partly retained during the subsequent aging process because of lower temperature and short aging time, and the remaining martensite and microstructural defects can help maintain high strength. What’s more, a small part of defects disappeared during this incomplete aging process due to martensite decomposition and recovery, which was beneficial to ductility.

Using multi-scale interaction mechanisms in yolk-shell structured C/Co composite materials for electromagnetic wave absorption

Advanced chemical engineering for simultaneous modulation of nanomaterial morphology, defects, interfaces, and structure to enhance electromagnetic and microwave absorption (MA) performance. However, accurately distinguishing the MA contributions of different scale factors and tuning the optimal combined effects remains a formidable challenge. This study employs a synergistic approach combining template protection etching and vacuum annealing to construct a controlled system of micrometer-sized cavities and amorphous carbon matrices in metal-organic framework (MOF) derivatives. The results demonstrate that the spatial effects introduced by the hollow structure enhance dielectric loss but significantly weaken impedance matching. By increasing the proportion of amorphous carbon, the balance between electromagnetic loss and impedance matching can be effectively maintained. Importantly, in a suitable graphitization environment, the presence of oxygen vacancies in amorphous carbon can induce significant polarization to compensate for the reduced conductivity loss due to the absence of sp2 carbon. Through the synergistic effects of morphology and composition, the samples exhibit a broader absorption bandwidth (6.28 GHz) and stronger reflection loss (−61.64 dB) compared to the original MOF. In conclusion, this study aims to elucidate the multiscale impacts of macroscopic micro-nano structure and microscopic defect engineering, providing valuable insights for future research in this field.

Effect of temperature gradient on the chemical structure and physical morphology of polyacrylonitrile fibers during thermal stabilization process

The thermal stabilization process is a crucial stage for microstructure transformation and quality of carbon fibers, which is determined by the stabilization temperature gradient. In this work, the effect of the temperature gradient on the evolution of both chemical structures and physical morphology of polyacrylonitrile (PAN) fibers at multistage of thermal stabilization process was investigated. Combined with functional groups, oxygen element content, and aromatization index, increasing temperature reasonably shifted oxidation and cyclization reaction into early stage and the corresponding samples possessed relatively large degree of cyclization. It was worth noting that high stabilization temperature gradient could accelerate the formation of the conjugated structures at early stage and facilitate the cyclization reaction in the stabilized fibers. As for morphologies, there were aligned microfibrils and transvers lamellae in stabilized fibers. Their radial structure difference increased firstly and then decreased in the later stage. The tensile strength and tensile modulus decreased during the thermal stabilization process. Moreover, increasing temperature resulted in reduction of tensile strength and tensile modulus, which was mainly resulted by the high degree of cyclization instead of structural defects. These results guide the design and optimization of temperature program and adjusting the processing parameters for all commercially PAN fibers without any additional conditions.

Electric-field-dependent electrical properties and domain switching of 0.92BNT-0.08BT ceramic coatings

Bi0.5Na0.5TiO3-based ferroelectric materials with strong ferroelectricity and high Curie temperature have great application prospects in modern microdevices. In this paper, 0.92BNT-0.08BT ceramic coating was prepared by supersonic plasma spraying. The phase, microstructure, electrical properties and domain response of 0.92BNT-0.08BT ceramic coating were analyzed. The findings demonstrate that the 0.92BNT-0.08BT ceramic coating is without obvious structural defects and has a completely structure with good interface bonding. 0.92BNT-0.08BT ceramic coating has good electrical properties, the dielectric constant is 417, the dielectric loss is 0.3, and the remnant polarization is 16.6μC/cm2. The piezoelectric force microscopy (PFM) results show that the 0.92BNT-0.08BT ceramic coating generally exhibits irregular and inhomogeneous striped nanodomains, with significant changes in amplitude and phase response under different electric fields. The results using switching spectroscopy-piezoresponse force microscopy (SS-PFM) show that the local piezoelectric coefficient (PRmax) of the 0.92BNT-0.08BT ceramic coating reaches 754.3 pm/V at a voltage of 20 V, and the ferroelectric domains exhibit a clear switching behavior.

Proton-irradiation on graphene-SnO2 hybrid nanocomposites to boost NO2 gas sensing properties

Promising role of high-energy proton-irradiation (2 MeV) on graphene-SnO2 hybrid nanocomposites for NO2 sensing were demonstrated. We synthesized hybrid nanocomposites by using SnO2 nanoparticles and graphene flakes, being obtained from expandable graphite. NO2 gas sensing evaluations, with doses of 1 × 1012, 1 × 1013, and 1 × 1014 ions/cm2, displayed that the sensing device irradiated with a dose of 1 × 1013 ions/cm2 exhibited the highest performance at 200°C. Generation of structural defects and graphene-SnO2 heterojunctions were accounted for sensing enhancement. Calculations in regard to density functional theory revealed that the presence of defects enhanced the NO2 sensing of the optimized sensor. Besides considering defects in the graphene, we calculated the generation of SnO2-related defects, indirectly affecting the sensing characteristics.

Advancement of data-driven SHM: a research paradigm on AE-based switch rail condition monitoring

The past ten years have witnessed the tremendous progress of structural health monitoring applications in civil infrastructures. This is particularly embodied in railway engineering. The increasing train speed brings greater challenges to safety and ride comfort, and the primary theme of maintenance has been gradually altered from offline inspection to online monitoring. Rail operators must get an in-time warning of potential structural defects before critical failure takes place. It is more favourable that the rail operators can take hold of the real-time status of the key components and infrastructures in railway systems. This paper summarizes a long-term research series by the authors’ research team on online monitoring of rail tracks at turnout areas utilizing acoustic emission-based sensing technique, and more importantly, successively advancing signal processing methods and data-driven analysing frameworks, covering Bayesian inference, convolutional neural networks, transfer learning and task similarity analysis. The proposed algorithms tackle noise interference brought by wheel-rail impacts, great uncertainties in an open environment, and insufficiency of monitoring data, and realize comprehensive monitoring of rail tracks in turnout areas from basic crack detection to regressive condition assessment step-by-step.

Atomically dispersed Au single sites and nanoengineered structural defects enable a high electrocatalytic activity and durability for hydrogen evolution reaction and overall urea electrolysis

The development of exceptionally active and stable trifunctional electrocatalysts is essential to facilitate industrial applications of proton exchange membrane electrolyzers. Rare earth catalysts have a wide range of applications in alkaline solution oxidation, but limitations in their stability and activity prevent their further application. In this paper, Au doped CeO2 coated porous Aux/CeO2 (x= 1,2,3) was designed as a three-function electrocatalyst with excellent performance and stability. At 1 M KOH conditions, both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) reactions exhibit excess potentials of 159.6 and 320.8 mV at a current density of 10 mA cm-2. In addition, when incorporated into an Au2/CeO2 (0.05 mmol, HAuCl4•4H2O) microparticles, the catalyst exhibits the potential of 1.42 V(10 mA cm-2) containing 0.33 M urea in 1 M KOH. Remarkably, for hydrogen production driven by urea electrolysis, Au2/CeO2 demonstrated exceptional performance by requiring only a voltage input of 1.63 V. The reducing agent that forms the Au/CeO2 heterojunction modulates the electronic structure of the Au active site and optimizes the adsorption of the intermediate. In addition, the interaction of the Au monolayer with the CeO2 nanosphere effectively prevents excessive oxidation and dissolution of Au, and the porous hollow structure provides additional exposed active sites and facilitates mass transfer.

Remediation of Alizarin Yellow GG from aqueous sources by Quasi-UiO-66; Box-Bencken design optimization and adsorption cherctization

This study develops a defect-engineered quasi-UiO-66 MOF adsorbent with enhanced performance for removing the organic dye Alizarin Yellow GG. Introducing structural defects and controlled thermal treatment to generate exposed metal sites significantly improved adsorption capacity, providing insights for designing advanced MOF adsorbents. This research successfully developed a controlled thermal partial ligand elimination. This process introduced structural modifications, forming additional open zirconium sites and hierarchical pores within the framework. These unique features contributed to the superior adsorption performance of the Q-UiO-66 adsorbent towards the organic dye Alizarin Yellow GG, exhibiting an unprecedented uptake capacity of 398.2 mg.g−1. Comprehensive characterization techniques, including FT-IR, FE-SEM, BET, XRD, and elemental analyses, were employed to understand the adsorbent’s properties. Furthermore, the optimization of the adsorption process was done using the Box-Behnken design approach, and the adsorption behavior was well-described by the Langmuier-Freundlich isotherm and pseudo-second-order kinetic models. The findings highlight the significant potential of this novel, defect-engineered Q-UiO-66 MOF adsorbent for effective dye removal applications.

Synthesis of Eu-doped TiO<sub>2</sub> nanoparticles by hydrothermal method

Purpose of research. Synthesis, characterization and comparison of the photocatalytic properties of europium-doped titanium dioxide nanoparticles. Methods. Europium-doped titanium dioxide nanoparticles were synthesized via a hydrothermal method followed by post-treatment processes including washing and annealing. Characterization was conducted using transmission electron microscopy, X-ray phase analysis, and energy-dispersive analysis. The bandgap width of the nanoparticles was determined through diffuse reflectance spectroscopy. Photoluminescence properties were studied using scanning probe microscopy and Raman spectroscopy. The photocatalytic properties were studied by spectrophotometry to determine the degradation of methylene blue under ultraviolet radiation. Results. Transmission electron microscopy identified the average particle sizes of europium-doped titanium dioxide. Using X-ray phase analysis, it was established that the nanoparticles were in the anatase phase regardless of the europium content percentage. Energy-dispersive spectroscopy confirmed the presence of the dopant in the samples. The photoluminescence intensity peak increased proportionally with the increase in europium content percentage. The strongest photocatalytic properties were exhibited at the lowest europium content among the samples studied. Conclusion. Synthesized and processed europium-doped titanium dioxide nanoparticles with anatase polymorphic modification exhibit photoluminescent properties. The luminescence intensity depends on the concentration of europium in the particles, due to the formation of additional energy levels inside the band gap. The photocatalytic properties of europium-doped nanoparticles are significantly improved in comparison with samples synthesized without impurities. However, a europium concentration above 0,5% leads to the growth of structural defects that reduce the mobility of photogenerated charge carriers and creates a high energy barrier that prevents them from reaching the surface.

Transforming an Ionic Conductor into an Electronic Conductor via Crystallization: In Situ Evolution of Transference Numbers and Structure in (La,Sr)(Ga,Fe)O3‐x Perovskite Thin Films

AbstractMixed‐conducting perovskites are workhorse electrochemically active materials, but typical high‐temperature processing compromises their catalytic activity and chemo‐mechanical integrity. Low‐temperature pulsed laser deposition of amorphous films plus mild thermal annealing is an emerging route to form homogeneous mixed conductors with exceptional catalytic activity, but little is known about the evolution of the oxide‐ion transport and transference numbers during crystallization. Here the coupled evolution of ionic and electronic transport behavior and structure in room‐temperature‐grown amorphous (La,Sr)(Ga,Fe)O3‐x films as they crystallize is explored. In situ ac‐impedance spectroscopy with and without blocking electrodes, simultaneous capturingsynchrotron‐grazing‐incidence X‐ray diffraction, dc polarization, transmission electron microscopy, and molecular dynamics simulations are combined to evaluate isothermal and non‐isothermal crystallization effects and the role of grain boundaries on transference numbers. Ionic conductivity increases by ≈2 orders of magnitude during crystallization, with even larger increases in electronic conductivity. Consequently, as crystallinity increases, LSGF transitions from a predominantly ionic conductor to a predominantly electronic conductor. The roles of evolving lattice structural order, microstructure, and defect chemistry are examined. Grain boundaries appear relatively nonblocking electronically but significantly blocking ionically. The results demonstrate that ionic transference numbers can be tailored over a wide range by tuning crystallinity and microstructure without having to change the cation composition.

Visualizing Structural Defects at Hidden Interfaces of Micro-Optoelectronic Devices by Second Harmonic Generation Microscopy

Visualizing Structural Defects at Hidden Interfaces of Micro-Optoelectronic Devices by Second Harmonic Generation Microscopy

Designing tribotechnical epoxy composite materials reinforced with chopped fibers and modified with silicon organic varnish

The object of research is modified epoxy composite materials containing fibrous fillers treated in physical fields. The technological features of the development of tribotechnical epoxy composites, which must withstand the effects of elevated temperatures, have been considered. In this case, it is necessary to modify the structure of the epoxy polymer matrix, which is achieved as a result of the introduction of heat-resistant organosilicon varnish. Organosilicon varnishes and chopped fibers contain technological additives, which complicates the process of structuring epoxy composites and leads to the appearance of structural defects. Removal of technological additives and cleaning the surface of the aramid and glass fibers from lubricants is possible as a result of processing the components of the composition in physical fields. There is a need to study the influence of physical fields on the structuring processes of the epoxy system and the formation of the structure of epoxy composites with specified properties. Modified epoxy composites contain chopped aramid and glass fibers treated with ultrasound. The tribotechnical characteristics of epoxy composites were studied at a sliding speed of V=1.0 m/s with a change in specific load from 0.5 MPa to 1.5 MPa. The temperature in the tribocontact zone during frictional interaction rises to 100 °C with an increase in the specific load. An increase in the density of the surface layer of tribocontact of epoxy composites with fillers treated in physical fields was revealed. The practical recommendations have been compiled for the implementation of the treatment technology of components in physical fields, which ensures structuring of epoxy composites with high tribotechnical characteristics

Designing tribotechnical epoxy composite materials reinforced with chopped fibers and modified with silicon organic varnish

The object of research is modified epoxy composite materials containing fibrous fillers treated in physical fields. The technological features of the development of tribotechnical epoxy composites, which must withstand the effects of elevated temperatures, have been considered. In this case, it is necessary to modify the structure of the epoxy polymer matrix, which is achieved as a result of the introduction of heat-resistant organosilicon varnish. Organosilicon varnishes and chopped fibers contain technological additives, which complicates the process of structuring epoxy composites and leads to the appearance of structural defects. Removal of technological additives and cleaning the surface of the aramid and glass fibers from lubricants is possible as a result of processing the components of the composition in physical fields. There is a need to study the influence of physical fields on the structuring processes of the epoxy system and the formation of the structure of epoxy composites with specified properties. Modified epoxy composites contain chopped aramid and glass fibers treated with ultrasound. The tribotechnical characteristics of epoxy composites were studied at a sliding speed of V=1.0 m/s with a change in specific load from 0.5 MPa to 1.5 MPa. The temperature in the tribocontact zone during frictional interaction rises to 100 °C with an increase in the specific load. An increase in the density of the surface layer of tribocontact of epoxy composites with fillers treated in physical fields was revealed. The practical recommendations have been compiled for the implementation of the treatment technology of components in physical fields, which ensures structuring of epoxy composites with high tribotechnical characteristics

Amorphous Cobalt-Impregnated Nitrogen-Doped Carbon Encapsulation Nanochain Enhances Long-Lasting Electrochemical Water Splitting.

Electrochemical water splitting (EWS) is a promising way to attain H2, which has been deemed an ideal substitution for fossil fuels because of renewable and eco-friendly benefits. Developing an amorphous-based simple and structurally flexible non-noble catalyst to offer high performance for commercial applications has become a current interest. Amorphous cobalt-anchored nitrogen-doped carbon nanoparticles (Co@NC-NPs) were designed to have a low overpotential and Tafel as a bifunctional electrocatalyst (HER - 142 mV/80 mV dec-1 and OER - 250 mV/72 mV dec-1) to achieve 10 mA cm-2 in 1.0 KOH. FE-SEM and HR-TEM described the interconnected nanochain morphology and purity of Co@NC-NPs electrocatalyst, which were confirmed by EDX and elemental mapping. In a full cell water electrolyzer, Co@NC-NPs(+,-) may act as an anode and cathode electrode material to achieve 1.60 V @ 10 mA cm-2 in a wide pH. The efficient Co@NC-NPs are stable for 100 h without obvious recession. In solar cell applications, Co@NC-NPs(+,-) catalyst was employed as both positive and negative terminals and evolved enormous bubbles of O2 and H2. As previously mentioned, we covered the amorphization strategy with the optimistic role of structural flexibility and defects to enrich the active sites to improve the electrocatalytic stability. As a promising opinion, the amorphous electrocatalyst provides ultraefficiency for forthcoming developments in EWS.

The influence of heavy doping of TiCoSb intermetallic semiconductor with Cr atoms on structural, kinetic and energetic properties

The structural, electrokinetic, and energetic properties of the TiСо1-xCrxSb semiconductor obtained by doping TiCoSb with Cr atoms introduced into the structure by substituting Co atoms in the crystallographic position 4c were studied. It was shown that in TiСо1-xCrxSb the structural defects of donor and acceptor nature are generated simultaneously in different ratios depending on the impurity concentration. At concentrations of х ≥ 0.02, the conductivity of TiСо1-xCrxSb has a metallic character, and the contribution of current carrier scattering mechanisms to the value of electrical resistivity is of the same order as changes in the concentration of current carriers. It was established that at all temperatures in the range of concentrations x = 0–0.02, the rate of generation of donors exceeds the rate of generation of acceptors, and at concentrations x > 0.02, on the contrary, the rate of generation of acceptors is greater than that of donors. This is indicated by the positive values of thermopower coefficient α(х,Т) of TiСо1-xCrxSb for х > 0.03.