Electron Microscopy Investigations Research Articles

Structural, bandgap tailoring, photoluminescence and electrochemical characteristics of Sm3+-doped ZnS quantum dots prepared in Ar-atmosphere

Sm3+-doped ZnS quantum dots were prepared by a cost-effective, simple co-precipitation technique under an argon atmosphere. The prepared Sm3+-doped QDs exhibited a cubic structure with an average particle size of ∼ 2 nm, as confirmed through X-ray diffraction and high-resolution transmission electron microscopic investigations. The crystallite was reduced and strain produced due to the larger ionic radius of Sm3+ ions. The Sm (at. 2 %)-doped ZnS exhibited a blue shift, and the optical transmittance was enhanced. A highly intense red emission was obtained in photoluminescence investigations, and this is due to the transfer of photons from 4G5/2 → 6H11/2 for f-f transitions of the Sm3+ in the 4f5 configuration. The obtained photoluminescence emissions lead to red phosphor applications. The cyclic voltammogram analysis showed that adding Sm to ZnS QDs made their specific capacitance value higher and it found potential applications in supercapacitors.

Towards Using Polybenzidine-Graphene Oxide Sheet on Graphite as a New System for Supercapacitor Device Fabrication

Polybenzidine-anodic exfoliated graphene oxide sheet (PB/AEGO Nsh) graphite sheet electrode was easily fabricated via electrochemical anodization of the graphite sheet followed by in situ chemical polymerization of benzidine on the anodized graphite sheet. Fourier transform infrared spectroscopy, dispersive Raman spectroscopy, and scanning electron microscopy investigations confirm that benzidine is successfully polymerized on the graphene oxide sheets created by the anodizing process. Evaluating the electrochemical performance of PB/AEGO Nsh graphite sheet electrode shows that the electrode has an excellent specific capacitance of about 841.89 mF cm−2 at 1 mA cm−2 in aqueous 1.0 M H2SO4 electrolyte. To check the applicability of the constructed electrode, a solid-state symmetric supercapacitor device separated by PVA/H2SO4 gel electrolyte was fabricated and its electrochemical performance was checked. Investigation of the capacitance behavior of the fabricated supercapacitor device indicates that the device has an excellent specific capacitance of about 334.7 mF cm−2 (230.11 F g−1) at 1 mA cm−2, maximum specific energy, and power density of 225 mWh cm−2 and 5000 mW cm−2, and cyclic life of 76.7% after 10000 galvanostatic charge/discharge cycles with non-IR drop. PB/AEGO Nsh graphite sheet electrode shows great potential for use in energy storage devices.

Effect of surface roughness on corrosion behavior of AISI 4340 high-strength steel in sodium chloride solutions

In this work, an AISI 4340 high-strength steel alloy was surface machined to have four different grades of roughness (Ra). The impact of changing Ra on the corrosion of the steel alloy in 3.5% NaCl solutions after 40 min and 24 h was performed using various electrochemical techniques. The cyclic polarization experiments showed that an increase in Ra increases the steel corrosion via enhancing the corrosion current of the alloy. The electrochemical impedance plots also indicated that an increase in Ra reduces the corrosion resistance of the alloy by decreasing the diameter of the semicircle obtained by the Nyquist spectra. The change in potentiostatic current vs time measurements, which were obtained at −350 mV (Ag/AgCl), confirmed that pitting attack occurs and its intensity further increases with increasing Ra for all steel samples. An increase in immersion time also reduces the resistance to corrosion due to the iron dissolution from the surface of the steel alloy. After corrosion, the surface was analyzed using a scanning electron microscope and energy dispersive spectroscopy investigations.

Enhancing solubility and oral bioavailability of rosuvastatin through interpenetrating polymer network (IPN) nanogels: Fabrication, characterization, and in-vivo efficacy assessment

Rosuvastatin (RST) exhibits low aqueous solubility, presenting a challenge for its effective oral administration. The objective of this study is to improve the solubility of RST through the creation and assessment of interpenetrating polymer network (IPN) nanogels. The nanogels were produced via a free radical polymerization method, where hydrophilic polymers β-cyclodextrin (β-CD) and Poloxamer-407 (P407) were combined with the monomer 2-acrylamido-2-methylpropane sulfonic acid (AMPS). Comprehensive characterization of the nanogels included drug loading efficiency, solubility studies, zeta sizer measurements, sol-gel analysis, Fourier-transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), swelling studies, and in-vitro release analysis. Oral toxicity experiments were performed to verify the safety of the β-CD/Poloxamer-407-co-poly (AMPS) IPN nanogels when taken by mouth. The scanning electron microscopy (SEM) investigation unveiled a network structure characterised by porosity and sponginess. The thermal stability and complex synthesis of the nanogel components were validated by the FTIR, TGA, and DSC spectra. X-ray diffraction (XRD) analysis indicated a reduction in the crystallinity of RST within the nanogel matrices. The optimized nanogels formulation demonstrated a particle size of 185.71 ± 1.03 nm. Comparative studies with a reference product highlighted significant enhancements in drug solubility and release characteristics attributed to the fabricated nanogels. Toxicity assessments confirmed the non-toxic nature of the nanogels, supporting their biocompatibility. In-vivo studies using hyperlipidemic animal models validated the anti-hyperlipidemic efficacy of the developed nanogels. The nanogels' biocompatibility, high solubilization capacity, improved dissolution profile, rapid production process, and superior physicochemical properties underscore their potential as an effective oral delivery system for lipophilic drugs.

Detection of water pollutants using super-hydrophobic porous silicon-based SERS substrates.

Super hydrophobic porous silicon surface is prepared using a wet chemical synthesis route. Scanning electron microscopic investigation confirms a correlation between pore size and reaction time. SERS substrates are prepared by silver nanoparticle deposition on porous silicon surface. They exhibit excellent characteristics in terms of sensitivity, reproducibility, stability, and uniformity. They could detect rhodamine 6G in femtomolar range with SERS enhancement factor of ~ 6.1 × 1012, which is best ever reported for these substrates. Molecule-specific sensing of water pollutants such as methylene blue, glyphosate, andchlorpyrifos, is demonstrated for concentrations well below their permissible limits along with excellent enhancement factors. Porous silicon substrate functionalized with Ag nanoparticles demonstrates to be a promising candidate for low-cost, long-life, reliable sensors for environmental conservation applications.

Effect of Microsphere Concentration on Catechin Release from Microneedle Arrays.

In this work, microspheres were developed by cross-linking glutaraldehyde in an aqueous gelatin solution with a surfactant and solvent. A poly(vinyl alcohol) (PVA) solution was produced and combined with catechin-loaded microspheres. Different microsphere concentrations (0%, 5%, 10%, and 15%) were applied to the PVA microneedles. The moisture content, particle size, swelling, and drug release percentage of microneedles were studied using various microsphere concentrations. Fourier transform infrared and scanning electron microscopy (SEM) investigations validated the structure of gelatin microspheres as well as their decoration in microneedles. The SEM scans revealed that spherical microspheres with a wrinkled and folded morphology were created, with no physical holes visible on the surface. The gelatin microspheres generated had a mean particle size of 20-30 μm. Ex vivo release analysis indicated that microneedles containing 10% microspheres released the most catechin, with 42.9% at 12 h and 84.4% at 24 h.

Neuron mapping in the Molly fish optic tectum: An emphasis on the adult neurogenesis process.

Teleost fish exhibit the most pronounced and widespread adult neurogenesis. Recently, functional development and the fate of newborn neurons have been reported in the optic tectum (OT) of fish. To determine the role of neurogenesis in the OT, this study used histological, immunohistochemical, and electron microscopic investigations on 18 adult Molly fish specimens (Poecilia sphenops). The OT of the Molly fish was a bilateral lobed structure located in the dorsal part of the mesencephalon. It exhibited a laminated structure made up of alternating fiber and cellular layers, which were organized into six main layers. The stratum opticum (SO) was supplied by optic nerve fibers, in which the neuropil was the main component. Radial bipolar neurons that possessed bundles of microtubules were observed in the stratum fibrosum et griseum superficiale (SFGS). Furthermore, oligodendrocytes with their processes wrapped around the nerve fibers could be observed. The stratum album centrale (SAC) consisted mainly of the axons of the stratum griseum centrale (SGC) and the large tectal, pyriform, and horizontal neurons. The neuronal cells of the SO and large tectal cells of the SAC expressed autophagy-related protein-5 (APG5). Interleukin-1β (IL-1β) was expressed in both neurons and glia cells of SGC. Additionally, inducible nitric oxide synthase (iNOS) was expressed in the neuropil of the SAC synaptic layer and granule cells of the stratum periventriculare (SPV). Also, transforming growth factor beta (TGF-β), SRY-box transcription factor 9 (SOX9), and myostatin were clearly expressed in the proliferative neurons. In all strata, S100 protein and Oligodendrocyte Lineage Transcription Factor 2 (Olig2) were expressed by microglia, oligodendrocytes, and astrocytes. In conclusion, it was possible to identify different varieties of neurons in the optic tectum, each with a distinct role. The existence of astrocytes, proliferative neurons, and stem cells highlights the regenerative capacity of OT. RESEARCH HIGHLIGHTS: The OT of the Molly fish exhibited a laminated structure made up of alternating fiber and cellular layers, which were organized into six main layers. Radial bipolar neurons that possessed bundles of microtubules were observed in the stratum fibrosum et griseum superficiale (SFGS). The stratum album central (SAC) consisted mainly of the axons of the stratum griseum centrale (SGC) and the large tectal, pyriform, and horizontal neurons. Inducible nitric oxide synthase (iNOS) was expressed in the neuropil of the SAC synaptic layer and granule cells of the stratum periventricular (SPV). Also, transforming growth factor beta (TGF-β), SRY-box transcription factor 9 (SOX9), and myostatin were clearly expressed in the proliferative neurons. The existence of astrocytes, proliferative neurons, and stem cells highlights the regenerative capacity of OT.

Creep anisotropy of additively manufactured Inconel-738LC: Combined experiments and microstructure-based modeling

The current lack of quantitative knowledge on processing-microstructure–property relationships is one of the major bottlenecks in today’s rapidly expanding field of additive manufacturing. This is centrally rooted in the nature of the processing, leading to complex microstructural features. Experimentally-guided modeling can offer reliable solutions for the safe application of additively manufactured materials. In this work, we combine a set of systematic experiments and modeling to address creep anisotropy and its correlation with microstructural characteristics in laser-based powder bed fusion (PBF-LB/M) additively manufactured Inconel-738LC (IN738LC). Three sample orientations (with the tensile axis parallel, perpendicular, and 45° tilted, relative to the building direction) are crept at 850 °C, accompanied by electron backscatter secondary diffraction (EBSD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) investigations. A crystal plasticity (CP) model for Ni-base superalloys, capable of modeling different types of slip systems, is developed and combined with various polycrystalline representative volume elements (RVEs) built on the experimental measurements. Besides our experiments, we verify our modeling framework on electron beam powder bed fusion (PBF-EB/M) additively manufactured Inconel-738LC. The results of our simulations show that while the crystallographic texture alone cannot explain the observed creep anisotropy, the superlattice extrinsic stacking faults (SESF) and related microtwinning slip systems play major roles as active deformation mechanisms. We confirm this using TEM investigations, revealing evidence of SESFs in crept specimens. We also show that the elongated grain morphology can result in higher creep rates, especially in the specimens with a tilted tensile axis.

Se Inter-Diffusion Limits Absorber Layer Grain Growth in CdSe - CdTe Photovoltaics

Diffusion of Se from the CdSe window layer into the CdTe absorber improves the short circuit current density by narrowing the band gap and increasing the carrier lifetime. Thicker CdSe layers, however, show a dramatic loss in photocurrent collection due to Se over-alloying. Electron microscopy investigations show that this decrease in performance is due to the formation of small grains (∼783 nm average diameter), which exhibit grain boundary porosity in the Se inter-diffusion region. The larger grain boundary area and void free surfaces give rise to higher levels of nonradiative recombination, and therefore, a lower photocurrent. It is proposed that the small grain size is due to a drag force exerted by segregated Se solute atoms on a moving grain boundary, while faster Se diffusion along the grain boundaries results in vacancy build up and porosity due to the Kirkendall effect. The results indicate that the device processing conditions must be carefully controlled such that the negative effects of Se alloying (i.e., smaller grains, Kirkendall voids) do not undermine its benefits. Published by the American Physical Society 2024

Comparative study between oxide/soft ferrite, oxide/hard ferrite, and soft/hard ferrite nanocomposites: structural, electrical, and magnetic properties

Three binary nanocomposites (NCs): (0.5NiO/0.5Ni0.5Zn0.5Fe2O4), (0.5NiO/0.5BaFe12O19), and (0.5Ni0.5Zn0.5Fe2O4/0.5BaFe12O19) were prepared using the co-precipitation method followed by the wet ball-milling technique. X-ray diffraction analysis showed the production of NiO and Ni0.5Zn0.5Fe2O4 single phases, while the α-Fe2O3 secondary phase appeared in the BaFe12O19 and the 0.5Ni0.5Zn0.5Fe2O4/0.5BaFe12O19 nanocomposite. The transmission electron microscopy investigation and the selected area electron diffraction demonstrated the presence of the nanocomposites’ constituent phases. x-ray photoelectron spectroscopy identified the oxidation states found in the prepared samples (Ba2+, Ni2+, Ni3+, Zn2+, Fe3+, and O2−). The bandgap values (Eg) of the nanocomposites are in the range between 2.79 and 3.66 eV, which indicates their semiconductor nature. The DC conductivity experiment confirmed the semiconducting nature of all samples, and the activation energies ( EaH ) and ( EaL ) at high and low-temperature regions, respectively, were calculated from the Arrhenius equation. According to the vibrating sample magnetometer, the NCs exhibited ferromagnetic (FM) as showed by the M-H loops. In the oxide/soft ferrite NC, the dM/dH curve indicated strong exchange coupling interactions, while the hard and the soft magnetic phases in the oxide/hard ferrite and the soft/hard ferrite NCs were weakly exchanged coupled. Significant uses had been found for each of the three nanocomposites according to their constituent phases and properties.

Assessing lunar paleointensity variability during the 3.9 - 3.5 Ga high field epoch

Numerous paleomagnetic studies suggest that a lunar dynamo, with surface field intensities potentially as high as 40-100 µT, existed between ∼3.9 Ga and ∼3.5 Ga. This period is referred to as the High Field Epoch (HFE). However, the debate over the origin of magnetization recorded in lunar rocks still persists. In addition, whether the Moon could have sustained a continuously strong dynamo during the HFE remains unclear. To unravel the origin of magnetization preserved in lunar rocks and to better characterize the evolution of the ancient lunar dynamo, we conducted a comprehensive set of experiments including rock magnetic tests, electron microscopy, and paleomagnetic investigations on four HFE-aged Apollo 11 mare basalt samples: 10003, 10044, 10069, and 10071. Rock magnetic experiments and electron microscopy indicate that the remanence carriers are kamacite grains of varying sizes and domain states. Sample 10003 recorded a paleointensity of 54.10 ± 4.66 µT. Sample 10044, which was shocked (peak pressure >5 GPa), did not preserve a stable high coercivity remanent magnetization. Samples 10069 and 10071 recorded paleointensities of 61.46 ± 26.09 µT and 10.69 ± 2.87 µT, respectively. A series of hydrostatic pressure experiments, isothermal remanent magnetization (IRM) acquisition experiments, and viscous remanent magnetization (VRM) tests preclude the possibility of our samples containing shock remanent magnetization from transient impact-generated fields, IRM acquisition from exposure to spacecraft fields, and VRM acquisition from exposure to the Earth magnetic field. Overall, our study suggests that the source of these magnetizations was likely the lunar dynamo and may indicate nearly order-of-magnitude magnetic field fluctuations during the HFE.

Visible light enhanced selective benzene response of hexagonal atomic structured CuS microcloves

We have reported CuS microcloves (MCs) for highly selective detection of benzene using scanning kelvin probe (SKP) technique. The electron microscopy investigations revealed the formation of clove shaped CuS with a size of about 1–2 µm at 180 °C and 6 h. The time of reaction significantly affected the crystallinity as well as the morphology of resulting CuS materials. The investigations on adsorption behavior of different types of common volatile organic compounds (VOCs) with varying charge and nature revealed an outstanding selectivity towards benzene when compared to other VOCs. The difference in work function between gold tip and sensor surface modified with CuS MCs was decreased under the exposure of light, most likely caused by transfer of electrons to conduction band of CuS under illumination of light. As a result, the CuS MCs showed enhanced photo response in visible light exposure in the presence of benzene. A chemiresistive type sensor device was fabricated using CuS MCs and exposed to benzene vapor in a concentration ranging from 2.8 to 11.2 ppm. The sensitivity was found to be 1.63 × 10-3 ppm−1. Notably, a rapid response time of ∼6 s and recovery time of ∼ 16 s was achieved for the sensor at a benzene concentration of 5.6 ppm at room temperature. Also, considerable and repeatable sensor response was observed for 560 ppb of benzene vapor at 70 °C. Hence, these results suggested that the CuS MCs have huge potential as novel material for selective benzene detection in gas phase towards breath analysis and other environmental monitoring.

Scanning electron microscopic investigation on Chicory tribe (Compositae) botanical sources and their antimicrobial potential.

This study discusses the micro-level structural details of Cichorieae pollen sources elucidated by scanning electron microscopy (SEM) and explains their symmetry and morphometry. The in-depth knowledge from the electron ultrastructure of Asteraceae pollen has provided insights into enhanced pollen morphology, and the antimicrobial significance of species under study presents novel avenues for their natural defense mechanisms in the development of antimicrobial agents. In this research, both quantitative and qualitative features of pollen were examined. The pollen grains are prolate-spheroidal and oblate-spheroidal in shape, characterized by a maximum polar diameter of 55.6-61.0 μm and a maximum equatorial distance of 68.3-74.4 μm. SEM reveals various configurations such as echinate perforate-tectate, psilate, and echino-lophate perforate. The Cichorieae species have significant antimicrobial efficacy and are promising sources for the development of novel antimicrobial drugs with potential implications in pharmaceutical and healthcare industries. SEM analysis of Cichorieae pollens has provided remarkable insights into their unique structures, revealing diverse shapes and surface ornamentations, which can be used for accurate Asteraceae species identification. RESEARCH HIGHLIGHTS: SEM provides unique pollen surface structures and patterns of Chicory pollen grains. Chemical composition of Chicory botanical sources provides valuable information on their potential as antimicrobial agents. SEM imaging reveals specialized fenestrate grain structures of taxonomic importance.

An investigation into the effect of UV irradiation and biofilm colonization on adsorption and desorption behavior of polyurethane (PU) microplastics for bisphenol A (BPA)

Recent studies have demonstrated that microplastics (MPs) can act as a transport vector for pollutants in the environment. However, most studies have focused on carbon-carbon backbone polymers, with little known about heteroatom backbone polymers. In this study, polyurethane (PU) MPs were modified by UV irradiation and microorganism colonization to assess the different aging treatments on the interaction behavior (adsorption/desorption) between PU MPs and bisphenol A (BPA). The results of the adsorption kinetics experiment illustrated that the adsorption process of BPA could be described well by a pseudo-second order kinetic equation on both fresh and aged PU MPs. Although fresh PU MPs revealed the highest saturated adsorption capacity, at low BPA exposure concentrations (≤ 100 μg/L) the adsorption capacities for UV aged and biofilm colonized PU MPs were very similar to fresh MPs or even slightly higher than for fresh MPs, the main adsorption mechanisms including H-bonding interactions and π–π interactions. Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) investigations suggested obvious physicochemical property changes (e.g., generation of new functional groups, erosion, etc.) after UV irradiation and biofilm colonization. This study also showed that different exposure environments (ultrapure water, artificial seawater, simulated gastric fluid) could affect BPA adsorption/desorption via hydrophobic and electrostatic interaction on PU surfaces. These results further clarify the adsorption mechanisms of BPA on PU MPs that have undergone different aging treatments, and provides a theoretical basis for the assessment of environmental behavior and exposure risks when PU MPs and BPA coexist.

Copper oxide nanoparticles-mediated Heliotropium bacciferum leaf extract: Antifungal activity and molecular docking assays against strawberry pathogens

Abstract In the current study, Heliotropium bacciferum leaf extract was used to biosynthesize copper oxide nanoparticles (CuO-NPs). Various analytical techniques were used to characterize the produced CuO-NPs. Transmission electron microscope investigation indicated well-distributed spherical particles in various development phases. The particles’ diameters ranged from 22.15 to 37.01 nm, with an average of 24.8 ± 6.1 nm. Energy dispersive X-ray examination confirmed the presence of nanoscale Cu ions at a high concentration, as seen by the strong signal peak at 1 keV. Fourier transform infrared spectrum revealed various functional groups on the green-produced CuO-NPs, as evidenced by multiple absorption beaks. The bands found at 3,195 and 2,916 cm−1 revealed that phenolic and flavonoid compounds’ alcohols and alkanes were stretching C–H. Also, a band at 1,034 cm−1 is typically attributed to CuO production. CuO-NPs exhibited significant bioactivity against isolated and molecularly identified fungal strains, including Rhizoctonia solani (OR116528), Fusarium oxysporum (OR116508), and Botrytis cinerea (OR116491). Remarkably, the highest inhibition percentages were recorded at 100 µg/mL, with values 81.48, 71.11, and 50.74% for R. solani, F. oxysporum, and B. cinerea, respectively. Molecular docking interactions revealed that the highest binding affinity of CuO-NPs was −5.1 for the oxidoreductase of B. cinerea and −5.2 and −5.4 for the chitin synthase of R. solani and F. oxysporum, respectively. Consequentially, the biosynthesized CuO-NPs could be employed as antifungal biocontrol agents, as well as using H. bacciferum leaf extract for the synthesis of nanoparticles for various sustainable agricultural applications.

Advancing structure − property homogeneity in forged Alloy 718 engine disks: A pathway towards enhanced performance

Alloy 718 is widely used in critical temperature components of modern aircraft engines and gas turbines. However, its industrial-scale forging faces challenges around heterogeneous microstructures and properties in the final product. This has been attributed to inherent heterogeneous microstructures of the billet starting materials and/or the heterogeneous nature of deformation during hot forging itself, leading to heterogeneities and inferior mechanical performance during service.To overcome these challenges, a three-step TMP approach, denoted simply as TMP3, is introduced to unlock effective microstructure and homogeneity control, irrespective of the given billet microstructure. Using electron and atom probe microscopy, the through-process microstructure evolution is revealed, highlighting dependencies of homogeneity and superior properties on various dynamic recrystallization mechanisms and the δ-phase dissolution. The process affects the dislocation density, δ-phase characteristics, and solute distribution in the matrix γ-phase. This facilitates Nb redistribution, resulting in fractions and morphologies of γʹ and γ“ Co-precipitates during subsequent direct ageing. The final samples have a hardness of ∼ 500 HV, a ∼ 5 % improvement over previous methods, providing a reliable proxy for high-temperature yield strength, independent of the billet position. Our TMP3 approach can be scaled-up and will enable manufacturing of high-performance Alloy 718 parts ready for next generation aircraft engines.

In situ high-temperature transmission electron microscopy investigation of dynamic element migration for Sm-Co-Fe-Cu-Zr sintered magnets

The investigation delved into the dynamic migration of elements and the evolution of interface structures within the Sm(CobalFe0.09Cu0.09Zr0.03)7.2 magnet as temperature increased, employing high-temperature transmission electron microscopy. Notably, the Cu distribution exhibited temperature susceptibility. Elevating the temperature from room temperature (RT) to 400 °C led to a notable expansion in the distribution width of Cu, ranging from 28.5 to 50.8 nm. Simultaneously, the average Cu content at the cell boundaries decreased from 14.4 to 11.6 at.%. According to the high-temperature in-situ experimental results of the transmission electron microscopy thin-film samples, the derived diffusion coefficients, D300°Cand D400°C, were determined as 0.0525 nm2/s and 1.414 nm2/s, respectively. The significantly higher D400°C compared to D300°C underscores the considerable influence of temperature on Cu element diffusion behavior. The simulation results demonstrate that the trend of magnetic properties variation at different temperatures closely aligns with the observed trend. Subsequent calculation of the temperature coefficient of intrinsic coercivity (β) reveals that |β300–400°C| is notably higher than |βRT-300°C|. This suggests a substantial impact of Cu diffusion-induced deterioration on the β. Moreover, micromagnetic simulation results delineated the reverse magnetization process for magnets at varying temperatures, revealing that the presence of the Cu diffusion region diminished the pinning effect of the cell boundary phase. Furthermore, a wider Cu diffusion region facilitated easier magnetic moment reversal at the cell boundary phase, resulting in a marked deterioration of intrinsic coercivity. This elucidates that the formation of the Cu diffusion region stands as one of the primary reasons for the sharp decline in magnetic properties of Sm2Co17-type magnets under high-temperature conditions.

Stacking fault energy, thermal expansion behavior, and elastic coefficients of a single-crystalline CrFeNi medium-entropy alloy

The equiatomic CrFeNi alloy is considered to be a model single-phase face-centered cubic medium-entropy alloy. The Bridgman technique was employed to grow a single crystal of this alloy and its dilatation behavior and elastic properties were measured in the temperature range: 100 K–673 K. Based on transmission electron microscopy investigations, plastic deformation is initially caused by the glide of dissociated dislocations (Shockley pairs bounded by a stacking fault ribbon). From their dissociated widths, a stacking fault energy of 36 mJ∙m-2 was determined.

Structural Evolution of GaOx-Shell and Intermetallic Phases in Ga-Pt Supported Catalytically Active Liquid Metal Solutions.

We present a comprehensive scale-bridging characterization approach for supported catalytically active liquid metal solutions (SCALMS) which combines lab-based X-ray microscopy, nano X-ray computed tomography (nano-CT), and correlative analytical transmission electron microscopy. SCALMS catalysts consist of low-melting alloy particles and have demonstrated high catalytic activity, selectivity, and long-term stability in propane dehydrogenation (PDH). We established an identical-location nano-CT workflow which allows us to reveal site-specific changes of Ga-Pt SCALMS before and after PDH. These observations are complemented by analytical transmission electron microscopy investigations providing information on the structure, chemical composition, and phase distribution of individual SCALMS particles. Key findings of this combined microscopic approach include (i) structural evolution of the SCALMS particles' GaOx shell, (ii) Pt segregation toward the oxide shell leading to the formation of Ga-Pt intermetallic phases, and (iii) cracking of the oxide shell accompanied by the release of liquid Ga-Pt toward the porous support.

Stabilization of metastable γ-co: Combustion synthesis and rapid processing

This study reports a novel method for stabilizing the metastable γ-Co phase, which has a face-centered cubic structure. This phase is known for its challenging synthesis due to its tendency to transform into the stable hexagonal-closed packed (ε-Co) allotrope. Combustion synthesis and a rapid pressure-less sintering approach overcome the traditional barriers to γ-Co preparation. The combustion process involves exothermic reactions in a solution of cobalt nitrate hexahydrate and hexamethylenetetramine, generating enough heat to increase the synthesis temperature above the γ↔ε phase transition temperature (∼690 K). Rapid cooling of the solid product by gases is critical to preventing the reverse transition to ε-Co, thus stabilizing the γ-Co phase with a minimal amount of the stable phase. Thermal analysis has demonstrated that the decomposition of cobalt nitrates hexahydrate leads to the formation of cobalt oxides. These oxides are then reduced to Co by methane (CH4) and hydrazine (N2H4), released during hexamethylenetetramine decomposition. Kinetic data analysis shows that the rate-limiting step in forming Co is the CH4 (or N2H4)-mediated reduction of CoO. When subjected to rapid pressure-less sintering at 1275 K, the combustion synthesized materials consolidate into compact samples with a relative density of ∼90 % and micrometer-size grains. High-resolution electron microscopy investigation shows increased lattice dislocation due to the ε→γ transition at high-temperature processing. Prepared γ-Co exhibits a higher nanohardness and Young's modulus than ε-Co prepared by slow melt solidification and rolling methods.