Metallic Behavior Research Articles

Ca@Pb12: A Viable All-Main-Group-Metal Endofullerene That Imitates the Transition Metals.

Herein, we report the Ca@Pb12 cluster, an all-main-group-metal endofullerene possessing the highly symmetric icosahedral (Ih) Platonic solid structure. The endohedral environment endows the Ca atom with concrete transition-metal-like bonding behaviors, as evidenced by the 18e (in 3d104s24p6 configuration) valence shell structure and five strong Pb12 → Ca(3d) dative bonds, whose orbital interaction energy (ΔEorb, -134.2 kcal/mol) represents 54.9% of total ΔEorb (-244.4 kcal/mol) between Ca2+ and [Pb12]2-. Moreover, since the favorable orbital interactions can compensate for the enlarged steric repulsion during encapsulation, Ca@Pb12 is thermodynamically stable, dynamically rigid (up to 1300 K), and electronically robust, as verified by large HOMO-LUMO gaps (4.58 eV), high vertical detachment energy (6.39 eV), and low electron affinity (-0.71 eV). It is the first viable all-main-group-metal endofullerene, where the guest alkaline earth metal exhibits the typical bonding behaviors of transition metals.

Unlocking the potential of FeNbGe Half Heusler: stability, electronic, magnetic and thermodynamic properties

Abstract In this paper, we investigate the electronic, magnetic, mechanical, dynamical, and thermodynamical properties of novel FeNbGe half Heusler alloy by first principle calculations. The alloy’s thermodynamic and dynamic stability were verified, and it was found feasible to synthesize experimentally. The calculated elastic constants prove the mechanical stability of the material. The malleable and ductile nature of the material was confirmed through Pugh’s and Poisson’s ratios. The electronic properties were calculated using the GGA and TB-mBJ exchange-correlation potentials. The band structure in the spin-down channel reflects metallic behaviour. In contrast, the spin-up channel shows non-metallic behaviour, which infers the half-metallic property of our half-Heusler alloy, which is a desirable property for spintronic materials. The alloy displayed an indirect band gap of 1.06 eV from GGA and 1.15 eV from TB-mBJ functionals. The Heusler alloy under study with 17 valence electrons, was found to be a Ferromagnetic alloy with a total magnetic moment of −1μ B . The half-metallicity retaining property was studied by imposing expansive volumetric strain. The small band gap, half-metallic property, and the ferromagnetic nature of our material suggest that it can be a suitable material for spintronics applications.

Electrically tunable metal–semiconductor behavior in 2H-MoTe2

In this study, we report tunable metallic and semiconducting behavior in molybdenum di-telluride (2H-MoTe2) by manipulating the Joule heating process through electrical control of the channel current. At low voltages, 2H-MoTe2 exhibits semiconducting behavior. As the current surpasses a critical threshold at higher voltages, the material transitions to a metallic-like state, confirmed by a positive temperature coefficient of resistance. Temperature- and voltage-dependent Raman studies confirm that this semiconducting to metal-like transition occurs without any accompanying structural phase transformation. This metallic behavior is likely due to enhanced phonon scattering caused by the increase in lattice temperature. In the metallic state, exposure to H2 gas results in a negative response, with increased resistance due to additional phonon scattering. Conversely, laser exposure at this state produces no noticeable photoresponse because the already high lattice temperature limits the impact of further heating. These effects were suppressed when 2H-MoTe2 was placed on a hexagonal boron nitride/multilayer graphene heat sink. This dynamic modulation of conductivity in 2H-MoTe2 through electrical stimuli highlights its potential for nanoelectronic device applications.

Bias Dependence of the Transition State of the Hydrogen Evolution Reaction.

The hydrogen evolution reaction (HER) is one of the most prominent electrocatalytic reactions of green energy transition. However, the kinetics across materials and electrolyte pH and the impact of hydrogen coverage at high current densities remain poorly understood. Here, we study the HER kinetics over a large set of nanoparticle catalysts in industrially relevant acidic and alkaline membrane electrode assemblies that are only operated with pure water humidified gases. We discover distinct kinetic fingerprints between the iron triad (Fe, Ni, Co), coinage (Au, Cu, Ag), and platinum group metals (Ir, Pt, Pd, Rh). Importantly, the applied bias changes not only the activation energy (EA) but also the pre-exponential factor (A). We interpret these changes as entropic changes in the interfacial solvent that differ between acid and base and entropic changes on the surface due to a changing hydrogen coverage. Finally, we observe that anions can induce Butler-Volmer behavior for the coinage metals in acid. Our results provide a new foundation to understand HER kinetics and, more broadly, highlight the pressing need to update common understanding of basic concepts in the field of electrocatalysis.

Crystal structure and absence of magnetic order in single-crystalline RuO2

RuO2was considered for a long time to be a paramagnetic metal with an ideal rutile-type structure down to low temperatures, but recent studies on single-crystals claimed evidence for antiferromagnetic order and some symmetry breaking in the crystal structure. We have grown single-crystals of RuO2by vapor transport using either O2or TeCl4as transport medium. These crystals exhibit metallic behavior following aT2low-temperature relation and a small paramagnetic susceptibility that can be attributed to Pauli paramagnetism. Neither the conductance nor the susceptibility measurements yield any evidence for a magnetic or a structural transition between 300 K and ∼4 K. Comprehensive single-crystal diffraction studies with neutron and x-ray radiation reveal the rutile structure to persist until 2 K in our crystals, and show nearly perfect stoichiometry. Previous observations of symmetry forbidden reflections can be attributed to multiple diffraction. Polarized single-crystal neutron diffraction experiments at 1.6 K exclude the proposed antiferromagnetic structures with ordered moments larger than 0.01 Bohr magnetons.

Investigating the Multifunctional Role of Sr2FeMnO6 Double Perovskite in Spintronic and Thermoelectric Properties

Herein, the double‐perovskite Sr2FeMnO6 is investigated using density functional theory to investigate its electronic, magnetic, thermoelectric, and thermodynamic properties. The Sr2FeMnO6 show the ferromagnetic phase stability with the formation energy of about −2.53 eV. Spin‐polarized band structure and density of states (DOS) calculations, performed using the Perdew–Burke–Ernzerhof generalized gradient approximation (PBE‐GGA) and modified Becke–Johnson (GGA + mBJ) methods, confirm a half‐metallic nature. The system exhibits metallic behavior in the spin‐up channel, whereas the low‐spin counterpart demonstrates semiconducting characteristics with a bandgap of about 1.38 eV. A total magnetic moment of 7 μB per formula unit is observed, predominantly originating from Fe and Mn atoms, with induced magnetism in oxygen attributed to Mn‐3d, Fe‐3d, and O‐2p orbital interactions. The thermoelectric behavior of the system is studied by employing the semiclassical Boltzmann theory‐based BoltzTraP code for both spin channels, revealing zT values of 0.98 and 0.94 for spin‐down and spin‐up channels, respectively, with zT decreasing and the power factor increasing with temperature. These findings highlight Sr2FeMnO6 as a promising candidate for spintronics, spin dynamics, and energy‐harvesting applications, offering insights into its multifunctional potential.

Utilization of molybdenum tailings in subgrade materials: Orthogonal experiments, long-term leaching behavior of heavy metals, and environmental impact assessment

Utilization of molybdenum tailings in subgrade materials: Orthogonal experiments, long-term leaching behavior of heavy metals, and environmental impact assessment

Virtual texture analysis to understand microstructure effects on deformation twinning and detwinning behavior in BCC metals

Virtual texture analysis to understand microstructure effects on deformation twinning and detwinning behavior in BCC metals

Influence of coal slime on migration behavior and ecological risk of heavy metals during hydrothermal carbonation of sewage sludge

The heavy metals (HMs) presented in sewage sludge (SS) limit the application of SS hydrochar. Compare to SS, coal slime (CS) contains higher carbon, silicates and aluminates. Addition of CS during the hydrothermal carbonization (HTC) of SS can improve the quality of hydrochar, and facilitates better solidification of HMs. In this paper, the influence of CS on migration behavior and ecological risk of HMs during HTC of SS was investigated, and the environmental risks associated with HMs in co-hydrochar was assessed. The results showed that adding CS during SS HTC could lower the content of HMs in co-hydrochar, and compared to the total content of Cd, Cr, Cu and Zn in SS-240-1, the total contents of these HMs in S5C5-240-1 decreased by approximately 43.8, 51.6, 36.5, 42.8%, respectively. The addition of CS also could facilitate the transformation of HMs from bioavailable fractions to relatively stable fractions. The leaching concentration and bioavailability of HMs in hydrochar decreased substantially with the increase of reaction temperature and residence time, and the leaching concentration of Ni in S5C5-280-1 decreased by 83.7%, and the bioavailability concentration decreased by 89.5%. Interestingly, the results also showed that co-HTC of CS and SS could effectively reduce the ecological risk and the potential contamination level associated with HMs in hydrochar, and then reduced the potential environmental risk. The results of this study may provide theoretical basis for the solidification of HMs in hydrochar, as well as for clean and efficient utilization of SS and CS.

Anisotropic Hardening of HC420 Steel Sheet: Experiments and Analytical Modeling

Choosing the appropriate yield function is essential to precisely predicting the anisotropic hardening behavior of steel metals considering general loading directions. This research investigates the anisotropic hardening behavior of HC420 steel sheet by combining experimental and analytical modeling. Experiments are conducted for uniaxial tensile tests according to the three different directions and bulging tests to obtain hardening data. The experimental findings show that the loading direction affects the anisotropic behavior of HC420 steel’s strength and plastic deformation. The Chen-coupled quadratic and non-quadratic (Chen-CQN) approach is used to ensure the convexity of the HC420 steel. By comparing the Chen-CQN approach with the Yld2000-2d and Stoughton-Yoon’2009 yield functions, the Chen-CQN approach shows superiority in predicting the hardening behavior of the HC420 sheet, exhibiting a more straightforward numerical implementation and enhanced accuracy in yield stress predictions under different loading directions. Results from experimental hardening tests reveal that the Chen-CQN function precisely and flexibly characterizes the yield surface of HC420 steel, with a constant variation of within 2% from its predictions.

Distribution and transformation behavior of heavy metals and phosphorus during sewage sludge pyrolysis

Distribution and transformation behavior of heavy metals and phosphorus during sewage sludge pyrolysis

Soil remediation by co-disposal in sintered brick kilns: Migration characteristics of heavy metals in bricks and the kiln.

Rapid industrialization has led to the widespread accumulation of heavy metal-contaminated soils, posing significant environmental and health risks. Utilizing remediated soil for the production of sintered bricks offers a sustainable and effective solution. However, the migration and immobilization mechanisms of heavy metals during the sintering process, both within the tunnel kiln and the brick matrix, require detailed investigation. This study examined the distribution of heavy metals in the tunnel kiln and analyzed the differences in heavy metal content and leaching behavior between the inner and outer layers of the bricks. Bricks containing 15% remediated soil were prepared, and it was observed that the majority of heavy metals were effectively immobilized, with retention rates ranging from 90.6% to 99.9%. Selenium (Se), however, exhibited significant volatility, with a retention rate of only 64.3%. The outer layer of the brick body contained higher concentrations of As and Pb compared to the inner layer. Conversely, leaching tests showed lower leaching rates of Mn, Ni, Cu, and Zn in the inner layers, while As and Pb exhibited higher leaching rates in the inner layers. These findings underscore the varying migration and transformation behaviors of different heavy metals during sintering, both within the kiln and the brick layers. The study highlights the potential of doped sintered bricks as sustainable building materials, ensuring effective heavy metal stabilization with minimal environmental risk, and providing a promising pathway for the safe reuse of contaminated soils.

Enhancement of Strength and Hardness in Copper–Chromium–Zirconium Alloy Using Single‐Pass Multi‐Angular Twist Channel Extrusion: A Microstructural and Deformation Study

Herein, the strength and hardness of copper–chromium–zirconium alloy are enhanced in a single pass by a severe plastic deformation (SPD) technique called the multiangular twist channel extrusion (MATE) process. In equal channel angular pressing (ECAP) and twist extrusion (TE), requisite strain and uniformity are achieved through several extrusion passes. MATE is a single‐pass novel SPD technique developed by integrating TE with the ECAP followed by a direct channel zone. The deformation behavior of metal in the MATE process is elucidated through experimental and microstructural studies conducted in each zone. The MATE‐processed Cu–Cr–Zr alloy achieves a hardness of 184.4 Hv and a tensile strength of 645.2 MPa, reflecting an increase of 80.43% and 69.7%, respectively, relative to the annealed condition. The electrical conductivity of the MATE‐processed Cu–Cr–Zr alloy decreases to 74.29% International Annealed Copper Standard. The electron backscatter diffraction investigation reveals an average grain size of 2.8 μm, with 61% comprising low‐angle grain boundaries, while the calculated dislocation density, from X‐ray diffraction analysis, is 3.93 × 1014 m−2. The transmission electron microscopy image verifies the existence of dislocations and precipitates in the Cu–Cr–Zr alloy. The experimental and microstructural findings in each zone have aligned effectively.

Structural diversity and electronic properties of neodymium borides under high pressure.

Rare earth (RE) borides have garnered significant attention due to their high mechanical strength, superconductivity, and novel electronic properties. In this study, we systematically investigate the structural, electronic, and mechanical properties of RE neodymium borides across a wide range of pressures. Various stoichiometries of Nd-B compounds are predicted using the unbiased CALYPSO structure search method and density functional theory (DFT) calculations. Our findings indicate that the newly predicted NdB5, NdB7, and NdB8compounds are thermodynamically and mechanically stable at high pressures. Detailed analyses of the electronic band structure and density of states reveal that all neodymium borides exhibit metallic behavior. The hardness of the stable phases has been evaluated using an empirical model. Notably, NdB5compound could also be dynamically stable at ambient pressure with an estimated hardness of approximately 25 GPa, suggesting that NdB5is a potential hard metal boride. Our results provide valuable insights into the structural, electronic, and mechanical properties of Nd-B compounds, enhancing our understanding of their potential applications in various fields.

Investigation of Electronic and Spintronic Properties in Co-Doped Graphene Nanodisks for Spin Filtering Applications

Graphene nanodisks (GNDs) have attracted significant attention due to their unique electronic and magnetic properties, offering promising prospects for applications in nanoelectronics and spintronic devices. In this study, we investigate the density of states (DOS), spin currents, and spin polarization characteristics of pristine and Co-doped diamond-shaped and triangular GNDs using first-principles calculations. Our results reveal that Co doping induces spin splitting within the band gap of diamond-shaped GNDs, indicating spin-dependent phenomena. Additionally, fine spin splitting and metallic behavior are observed in the DOS of triangular GNDs. Through I-V curve analysis, we demonstrate that Co-doped diamond-shaped GNDs exhibit spin switch behavior and polarized spin currents, with a notable increase in peak current and polarization compared to pristine GNDs. The introduction of Co impurities enhances the spin filtering capabilities, making the device act as a spin filter in a wide voltage range. These findings provide valuable insights into the electronic and spintronic properties of Co-doped GNDs, offering possibilities for the development of efficient spintronic devices and spin filtering applications.

Integration of Finite Element Analysis and Machine Learning for Assessing the Spatial-Temporal Conditions of Reinforced Concrete

Composite reinforcements are attracting attention in the reinforced concrete (RC) field for their high corrosion resistance, low thermal conductivity, and low electromagnetic interference behavior. However, compared to metallic reinforcements, composites are less ductile and may lead to brittle failure. Three-point flexural tests provide information on the mechanical behavior of metal- and composite-reinforced concrete beams with distinct crack patterns. The structural conditions and failure mechanisms can be defined based on stress change and crack propagation. This study employs finite element analysis (FEA) to simulate the mechanical responses of composite- and metal-reinforced concrete beans under three-point flexural tests and predict the crack propagation in the beams. Machine learning-based algorithms are trained using FEA data to assess the spatial–temporal conditions of the RC beams. The findings indicate that composite rebars provide better reinforcement than metallic rebars in terms of stress fields (30.27% less stress in composite rebars) and crack propagation (fewer cracks in composite RC beams), with the initiation of shear cracks and maximum von Mises stress in rebars being correlated. The findings highlight the effectiveness of the Random Forest Regression (RFR) algorithm (R2=0.96) in assessing RC beam conditions under flexural loads, offering insights for efficient industry applications.

Thickness Dependence in Phase Formation and Properties of TaSe2 Layers Grown on GaP(111)B.

The effect of growth temperature and subsequent annealing on the epitaxy of both single- and few-layer TaSe2 on Se-terminated GaP(111)B substrates is investigated. The selective growth of the 1T and 1H phases is shown up to 1 ML according to X-ray and ultraviolet photoelectron spectroscopies. The 1H monolayer, favored at low temperatures, exhibits a very homogeneous coverage after annealing, while the 1T ML, grown at high temperatures, is characterized by a better in-plane orientation. Moreover, X-ray photoelectron diffraction spectroscopy performed on 1T submonolayers shows a negligible amount of mirror twins. By contrast, in multilayers, scanning transmission electron microscopy always reveals a mixture of 2Ha and 3R polytypes with very few 1T. In addition, the multilayers become Se-deficient above 500 °C, and a new interfacial phase identified as Ta1+xSe2 or TaP appears. Finally, the optimized multilayers grown between 250 and 500 °C exhibit a similar metallic behavior with a resistivity comparable to the bulk one with valuable outcomes in the formation of electrical contacts for two-dimensional (2D) material-based devices.

Determining the Parameters of Gurson–Tvergaard–Needleman Model for Predicting the Failure of Wrought and Fused Filament Fabricated 17-4 PH Stainless Steel

Abstract Metal additive manufacturing is an emerging technology for creating metallic parts, with metal fused filament fabrication (FFF) rapidly gaining popularity due to its cost-effectiveness. Despite the acceptable mechanical properties of additively manufactured metals using FFF, a significant technical challenge is the presence of undesirable porosity, which affects material performance. This study aims to model the material behavior of FFF 17-4 PH stainless steel, considering its porosity, using the Gurson–Tvergaard–Needleman (GTN) damage model. The GTN model, which incorporates the micromechanical behavior of ductile metals, shows great potential for failure prediction. The GTN model parameters were identified for both wrought and FFF 17-4 PH stainless steel through a series of proposed methods. Initial void volume fractions were determined using density measurements. The evolution of void volume fractions was experimentally assessed through interrupted uniaxial tensile tests, leading to the analytical derivation of three void nucleation parameters based on continuum damage mechanics. Additional GTN model parameters related to material failure were determined through microscopic analysis of rupture surfaces and finite element (FE) trial-and-error methods. FE simulations using the GTN damage model, represented as porous metal plasticity in abaqus, were conducted to verify the identified parameters. The results demonstrated that the numerical calculations of the FE model are in good agreement with the experimental data. The use of experimentally derived GTN model parameters from the proposed methods effectively predicts material behavior, particularly in the post-necking region where traditional FE modeling fails to simulate the realistic material response.

Enhancing hydrogen evolution by heterointerface engineering of Ni/MoN catalysts.

Molybdenum nitrides have garnered significant attention for their potential in the hydrogen evolution reaction (HER) due to their metallic behavior, abundant reserves, and pH-universal stability. However, their unsatisfactory hydrogen adsorption limits industrial applications. Heterostructures can be designed to introduce defects and modulate the electronic structure of catalysts to optimize hydrogen adsorption to enhance HER. Nevertheless, the exact active sites at the heterointerface and the fundamental mechanisms underlying the HER process remain inadequately understood. Herein, a composite electrocatalyst in which metallic Ni and MoN phases (Ni/MoN) form the heterointerface between them is fabricated. The heterointerface produces strong electronic interactions between Ni and MoN to facilitate electron transfer from MoN to Ni, and the built-in electric field facilitates charge transfer during electrocatalysis. This optimized electronic configuration with abundant active sites delivers excellent performance in alkaline HER. Density-functional theory calculations demonstrate that H2O dissociates at the Ni site, whereas H2 desorption occurs at the Mo site. As a result, Ni/MoN/CC requires an overpotential of only 95mV to achieve a current density of 10mA cm-2 and a Tafel slope of 104mV dec-1. Moreover, it maintains a high current density of 100mA cm-2 for 100h with negligible morphological or compositional changes. The strategy of modulating the electronic structure of low-cost, transition metal-based heterostructured electrocatalysts is an effective and commercially viable means to design and develop high-performance electrocatalysts for water splitting.

The effects of surface kink nucleation on the dislocation mobility for bcc metals: a kinetic Monte Carlo study

Abstract Dislocation plasticity in bcc metals at low temperatures and stresses is well known to be controlled by screw dislocation mobility. Screw dislocations move by the nucleation of kink-pairs on the dislocation line and is a relatively well studied phenomenon. However, how screw dislocation mobility is influenced by interfaces and surfaces has not been well-studied. To provide insight into the role interfaces play in screw dislocation mobility, this study proposes an empirical model to treat a grain boundary as a dislocation source, which is then implemented into kinetic Monte Carlo simulations for body-centered-cubic (bcc) metals. This effort focuses on the roles of kink nucleation and migration processes at the interface, comparing the energetics of these events on interfaces versus those on the interior of the dislocation line. The findings reveal that interfaces can either enhance dislocation motion or not affect it at all, depending on temperature, stress, and dislocation length. This work provides insights into the mesoscale behavior of bcc metals and bridges the gap between experimental observations and computational models at small scales.