Metallic Crystals Research Articles

Revealing the effect of 2D carbides with different metal sites for improving hydrogen storage in MgH2.

Two-dimensional (2D) carbon materials are considered as efficient catalysts for improving hydrogen storage in MgH2, but their catalytic mechanisms of different materials remain unclear. Herein we compare the hydrogen storage properties of MgH2 with doping different 2D carbon materials for revealing their catalytic effecting mechanisms. It can be seen that the effect of 2D metal carbides including Nb2C and Ti2C are superior to 2D graphene for improving hydrogen storage properties of MgH2, where the Ti2C exhibits the best catalytic effect with a remarkable decrease of activation energy (E a) from ∼124 kJ/mol for doping graphene to ∼86 kJ/mol. This is related to the changes of individual metal and graphite chemical valence states of catalysts. The high catalytic activity of the hydrogen storage reaction originates from its unique layered structure and in situ formation of MHX, i.e., the tiny metal crystals can serve as a channel to facilitate hydrogen transport in MgH2 matrix. Moreover, the Ti catalytic effect is better than Nb, which originates from the surface of the multivalent Ti atoms is an intermediate of the electron moving between H− and Mg2+, thus leading to the Ti2C catalyzed MgH2 with superior hydrogen kinetic and cyclic performance.

Rare-Metal Enrichment and Nb–Ta Fractionation during Magmatic–Hydrothermal Processes in Rare-Metal Granites: Evidence from Zoned Micas from the Yashan Pluton, South China

Abstract Rare-metal mineralization in aluminous granites (i.e. rare-metal granites, RMGs) is usually associated with high degree of magma fractionation, strong enrichment in fluxing elements (Li, B, P, and F), and the operation of both magmatic and hydrothermal processes. Experimental data have established the theoretical basis for melt- or fluid-driven rare-metal mineralization. To investigate these mechanisms in natural samples, this paper presents detailed textural and compositional variations for zoned micas and rare-metal minerals from rocks of the Late Jurassic Yashan rare-metal granitic pluton, South China. This pluton preserves an evolutionary sequence from ore-barren rocks to those containing ores formed by Ta–Nb–Li mineralization during magmatic–hydrothermal processes. Three main units of the Yashan pluton are exposed: from bottom to top, these comprise protolithionite–muscovite granite (Unit I), Li-mica granite (Unit II), and topaz–lepidolite granite (Unit III), representing crystallization from successive magma batches from a deep-level magma chamber. The gradual decrease in Nb/Ta and K/Rb in both whole rocks and micas from units I to II to III illustrates fractionation within the magma chamber, accompanied by successive enrichment of incompatible elements in the residual melt. Furthermore, the strong enrichment of fluxing elements such as Li, P, and F in Unit III likely led to lower magma viscosity, which may have helped to expulse interstitial residual melt from the magma chamber. Zoned micas from the Yashan pluton are composed of Li-phengite or lepidolite inner cores and muscovite rims. Cores show increasing Li, F, and rare-metal elements from units I and II to Unit III, consistent with the trend of magmatic fractionation. In contrast, rims that formed in the residual hydrosilicate melt show marked decrease in F and rare metals (i.e. Li, Cs, Rb, Nb, Ta, Sn, and W). Chemical variations of the zoned micas and rare-metal minerals were used together with Rayleigh fractionation modeling calculations to reconstruct the contribution of melt–fluid immiscibility to the crystallization of rare metals, which took place via the combination of melts enriched in high-field-strength elements (e.g. Nb and Ta) and fluids enriched in mobile elements (e.g. Mn, Fe, W, and Cs). Strong fractionation of Nb and Ta, along with extreme enrichment of Ta, in RMGs is caused mainly by the crystallization of micas and columbite-group minerals, and also depends on the degree of fractional crystallization. The subsolidus alteration of micas by acidic fluids may have leached some Nb rather than Ta during chloritization, which could have partly contributed to the enrichment of rare metals and fractionation of Nb–Ta. It is concluded that magmatic–hydrothermal processes, including magmatic evolution and fluid exsolution, are critical for rare-metal enrichment and Nb–Ta fractionation in RMGs.

L-PBF for the production of metallic phononic crystal: design and functional characterization

Vibration abatement often requires the adoption of peculiar solutions and/or foundations. This paper presents an innovative solution to this problem, consisting in a phononic meta-material realized via Laser Powder Bed Fusion (L-PBF) capable to prevent the propagation of vibrations within specific frequency ranges. The integration of this meta-material within existing supporting structures can, therefore, greatly reduce the needing of foundations capable to stop vibrations. After a description of the design procedure of the meta-material that shows how to satisfy the constraints imposed by L-PBF technology, the manufactured sample is described and analyzed to predict its band-gaps. Finally, the theoretical results are compared with experimental measurements. These results show a good agreement between expected and actual meta-material behavior.

First-principles theory of intrinsic spin and orbital Hall and Nernst effects in metallic monoatomic crystals

The generation of spin and orbital currents is of crucial importance in the field of spin-orbitronics. In this work, using relativistic density functional theory and the Kubo linear-response formalism, we systematically investigate the spin Hall and orbital Hall effects for 40 monoatomic metals. The spin Hall conductivity and orbital Hall conductivity (OHC) are computed as a function of the electrochemical potential and the influence of the spin-orbit interaction strength is also investigated. Our calculations predict a rather small OHC in $sp$ metals, but a much larger OHC in $d$-band metals, with maximum values $[\ensuremath{\sim}8000(\ensuremath{\hbar}/e)\phantom{\rule{0.28em}{0ex}}{(\mathrm{\ensuremath{\Omega}}\phantom{\rule{0.16em}{0ex}}\mathrm{cm})}^{\ensuremath{-}1}]$ near the middle of the $d$ series. Using the Mott formula, we evaluate the thermal counterparts of the spin and orbital Hall effects, the spin Nernst effect (SNE), and the orbital Nernst effect (ONE). We find that the as-yet unobserved ONE is significantly larger $(\ensuremath{\sim}10\ifmmode\times\else\texttimes\fi{})$ than the SNE and has maximum values for group 10 elements (Ni, Pd, and Pt). Our work provides a broad overview of electrically and thermally induced spin and orbital transport in monoatomic metals.

Molecular-scale mechanisms of CO2 mineralization in nanoscale interfacial water films.

The calamitous impacts of unabated carbon emission from fossil-fuel-burning energy infrastructure call for accelerated development of large-scale CO2 capture, utilization and storage technologies that are underpinned by a fundamental understanding of the chemical processes at a molecular level. In the subsurface, rocks rich in divalent metals can react with CO2, permanently sequestering it in the form of stable metal carbonate minerals, with the CO2-H2O composition of the post-injection pore fluid acting as a primary control variable. In this Review, we discuss mechanistic reaction pathways for aqueous-mediated carbonation with carbon mineralization occurring in nanoscale adsorbed water films. In the extreme of pores filled with a CO2-dominant fluid, carbonation reactions are confined to angstrom to nanometre-thick water films coating mineral surfaces, which enable metal cation release, transport, nucleation and crystallization of metal carbonate minerals. Although seemingly counterintuitive, laboratory studies have demonstrated facile carbonation rates in these low-water environments, for which a better mechanistic understanding has come to light in recent years. The overarching objective of this Review is to delineate the unique underlying molecular-scale reaction mechanisms that govern CO2 mineralization in these reactive and dynamic quasi-2D interfaces. We highlight the importance of understanding unique properties in thin water films, such as how water dielectric properties, and consequently ion solvation and hydration behaviour, can change under nanoconfinement. We conclude by identifying important frontiers for future work and opportunities to exploit these fundamental chemical insights for decarbonization technologies in the twenty-first century.

Melt sampling for hydrogen analysis optimized with the help of computer simulation

This research was carried out in laboratory conditions on a semi-continuous ingot casting machine owned by the Siberian Federal University. The paper compares the results of computer simulation carried out for AK12 alloy solidification process in the PoligonSoft programme. A new original mould is described designed for sampling liquid aluminium and its alloys for hydrogen analysis. The new mould has a larger surface area and walls that are made in the form of a heat exchanger intended for more efficient heat removal. It is shown that, in the commonly used Rensley mould, the melt solidifies in 14 seconds at the metal crystallization rate in the range from the pouring temperature to the solidus temperature of 15 oC/s, while in the case of the new mould these parameters are 12 seconds and 17.5 oC/s, correspondingly. The paper also compares the results of dissolved hydrogen analysis obtained when sampling was done with both the conventional Rensley mould and the new one. It was found that the concentration of hydrogen in the samples taken with the Rensley mould is lower on average by 0.01 cm3/100 g Al than in the samples taken with the new mould. Based on the results of the study, a conclusion was drawn that the proposed mould design delivers an additional advantage when sampling liquid metal. It also helps determine the concentration of dissolved hydrogen in molten aluminium with a higher degree of accuracy.This research was carried out by the Siberian Federal University as part of the governmental assignment for research; Project No. FSRZ-2020-0013.

Thermal convection in a rotating porous medium layer saturated by a nanofluid under a helical magnetic field

In recent years, experiments with flows of liquid metals in a helical magnetic field have been actively carried out. The study of the processes of mixing and crystallization of a liquid metal is of practical importance for metallurgy. With the development of nanotechnology, more and more new types of nanofluids (hybrid, ternary nanofluids) are being synthesized, and the thermophysical characteristics of which can compete with liquid metals. This circumstance served as a motivation for conducting this theoretical study. In this study, the criterion for the onset of convection in a Darcy–Brinkman porous medium layer saturated by an electrically conductive nanofluid under a helical magnetic field is investigated. The Brownian motion and thermophoresis effects are combined in the model for nanofluids, whereas the Darcy–Brinkman model is used for porous media. Instead of prescribing the nanoparticle volume fraction on the borders, we adopted a boundary condition in which the nanoparticle flow is considered to be zero. In the absence of a temperature gradient, a new type of instability in a helical magnetic field in a thin layer of a nanofluid is considered. The growth rate and the region of the development of this instability are numerically obtained depending on the profile of the azimuthal magnetic field (the magnetic Rossby number Rb) and the radial wave number k. In the presence of temperature, the stationary regime of nonuniformly rotating magnetoconvection is studied. The accurate analytical equation for the critical Rayleigh–Darcy number in terms of various non-dimensional parameters is determined using the linear stability theory. The results show that rotation and the axial (vertical) part of the helical magnetic field retard the onset of convection. While the azimuthal part of the helical magnetic field has a destabilizing effect at positive Rossby numbers Rb. The conditions for stabilization and destabilization of stationary convection in a helical magnetic field are determined for metal oxide, metallic, and semiconductor nanofluids.

A comparative study of 1D metallic (Au, Ag, Cu, Al) thermal tunable photonic crystal filter with exponentially graded thickness

A comparative study of 1D metallic (Au, Ag, Cu, Al) thermal tunable photonic crystal filter with exponentially graded thickness

Synthesis of single metallic crystal in microgravity simulated by static magnetic field

Static magnetic field is useful in processing materials with various microstructures. A self-designed gravity-assisted automatic docking device was used to study diffusion in liquid Al-Cu melts under various SMFs up to 22 T. SMF reduces the coefficient of interdiffusion (DAlCu) by damping the melt convection, which is more efficient with a horizontal SMF than a vertical SMF. A simulated microgravity is achieved when the SMF is greater than the critical 3 T. The simulated microgravity is in favor of growing a single α-Al dendrite in Al-Cu melt. The physical mechanism, which is called the diffusion-limited favored single crystal growth, is established. The present work provides a potential method in processing the single metallic crystal rapidly in the future.

Path Dependency of Plastic Deformation in Crystals: Work Hardening, Crystallographic Rotation and Dislocation Structure Evolution

This paper reviewed the research progress of studies on the crystal rotation of single crystals that were deformed by tension and shear and the influences of crystal rotation and dislocation evolution on strain hardening behavior in crystals that were deformed with different initial orientations. The crystal rotation is entirely different depending on whether the single crystal was deformed by tension or shear. A three-stage work hardening behavior, which is not one of the intrinsic properties of materials, is generated when FCC metallic single crystals are deformed by tension along unstable oriFigurFigurentations, but single crystals do not exhibit this three-stage hardening behavior when they are deformed by simple shear at room temperature. Under tension, crystal rotation causes the transition from work hardening stage I to stage II, while the transition from work hardening stage II to III is caused by dislocation evolution. The evolution of the dislocation structure is related to deformation loading and can be classified into three types when a crystal is deformed by tension. Different from tension, shear stress can directly act on one of the 12 slip systems when a crystal is deformed by simple shear. When FCC single crystals are deformed by shear along the (11¯1)[110], (111)[112¯] and (001)[110] orientations, the single slip system, co-planar slip systems and co-directional slip systems are activated, respectively, and the crystals hardly rotate under the shear conditions. The slip direction of [110] forces the crystal to rotate toward the shear direction under simple shear. The dislocation tangles tend to form the dislocation cells and wall structures when multiple slip systems are activated under simple shear.

New insights into the recrystallization behavior of large-size Mo–3Nb single crystal based on multi-scale characterization

The occurrence of recrystallization will cause catastrophic damage to the structure of metallic single crystal, which can be avoided by choosing crystal orientation reasonably. In this work, the effect of crystal orientation on the recrystallization behavior of single crystal is investigated using multi-scale characterization method. The electron backscattered diffraction analysis shows that in mesoscopic scale, the recrystallization behavior of Mo–3Nb single crystal exhibits a strong orientation dependence, which the new recrystallization grains are produced in the <111>-oriented single crystal, while the single crystal structure is still retained in other orientations. At the micro scale, the elongated dislocation cells with certain misorientations appear in the <111>-oriented single crystal, while only the dislocation walls and parallel dislocation cells distribute on the single crystal with the <110> and <112> orientations, respectively. The length of dislocation lines in deformed single crystal with <111> orientation is calculated using molecular dynamics to be 3491.22 Å, which is much longer than that of the <112> orientation (1133.27 Å) and the <110> orientation (2862.68 Å), suggesting a higher crystal distortion and easier recrystallization in the <111> orientation. In addition to the coalescence mechanism of discontinuous sub-grains, the shear band also plays an important role in promoting recrystallization nucleation. This work provides reference value for the secondary processing of molybdenum single crystal, so as to obtain more excellent products and expand its potential application.

Uncovering strong π-metal interactions on Ag and Au nanosurfaces under ambient conditions via in-situ surface-enhanced Raman spectroscopy

Uncovering strong π-metal interactions on Ag and Au nanosurfaces under ambient conditions via in-situ surface-enhanced Raman spectroscopy

Structure of χ3-Borophene Studied by Total-Reflection High-Energy Positron Diffraction (TRHEPD).

We have investigated the structure of χ3-borophene on Ag(111), a monolayer material of boron atoms, via total-reflection high-energy positron diffraction (TRHEPD). By comparing the experimental rocking-curves with ones for several structures calculated by using dynamical diffraction theory, we confirmed that the χ3-borophene layer has a flat structure. The distance from the topmost layer of the metal crystal is 2.4 Å, which is consistent with results reported by X-ray standing wave-excited X-ray photoelectron spectroscopy. We also demonstrated that the in-plane structure of χ3-borophene is compatible with the theoretical predictions. These structural properties indicate that χ3-borophene belongs to a group of epitaxial monolayer sheets, such as graphene, which have weak interactions with the substrates.

Effect of nanodisperse powders on the spreading and crystallization of a metal drop on a porous substrate

The influence of modifying nanopowders on the spreading and crystallization of a nickel droplet on a porous steel substrate is analyzed. For this purpose, a model has been developed for the spreading of a drop of liquid metal after its high-speed collision with a heated porous substrate. Due to the high impact velocity, the process of metal crystallization is considered after the complete spreading of the drop using the model of heterogeneous nucleation and macroscopic growth of the solid phase, taking into account the size and capillary effects. The influence of the impact velocity and substrate porosity on the thickness and diameter of the formed splat, the penetration depth, and the volume of liquid that penetrated the substrate has been studied. The numerical study of heterogeneous crystallization of a metal drop has made it possible to evaluate the influence of the modifying nanoparticle parameters, the impact velocity, and substrate porosity on the heterogeneous nucleation and on the resulting splat macrostructure.

Towards Perfect Ultra-Broadband Absorbers, Ultra-Narrow Waveguides, and Ultra-Small Cavities at Optical Frequencies.

In this study, we design ultra-broadband optical absorbers, ultra-narrow optical waveguides, and ultra-small optical cavities comprising two-dimensional metallic photonic crystals that tolerate fabrication imperfections such as position and radius disorderings. The absorbers containing gold rods show an absorption amplitude of more than 90% under 54% position disordering at nm. The absorbers containing silver rods show an absorptance of more than 90% under 54% position disordering at nm. B-type straight waveguides that contain four rows of silver rods exposed to air reveal normalized transmittances of 75% and 76% under 32% position and 60% radius disorderings, respectively. B-type L-shaped waveguides containing four rows of silver rods show 76% and 90% normalized transmittances under 32% position and 40% radius disorderings, respectively. B-type cavities containing two rings of silver rods reveal 70% and 80% normalized quality factors under 32% position and 60% radius disorderings, respectively.

Two-color photodetection of graphene-based transistors enhanced by metallic photonic crystals

Two-color photodetection of graphene-based transistors enhanced by metallic photonic crystals

Single‐Crystal Capacitive Sensors with Micropatterned Electrodes via Space‐Confined Growth of the Metal–Organic Framework HKUST‐1

AbstractThe polyhedral shape and fragile nature of single crystals of metal–organic frameworks (MOFs) hinder their processing using standard microfabrication techniques. As a result, the fabrication of surface patterns and microelectrodes on MOF single crystals is challenging, which limits both the direct electrical interrogation of crystals in research and their integration into optical and electrical devices. Herein, a new strategy to readily fabricate surface‐embossed micropatterns and surface‐embedded gold electrodes on MOF single crystals using a space‐confined, one‐step solvothermal synthesis is demonstrated. This method is based on the confined growth of the MOF crystal around prefabricated metal patterns with different adhesion strengths to the growth surface, producing features as small as 5 µm. As a proof of concept, micropatterns are created on flat single crystals of the MOF HKUST‐1, exhibiting the function as a diffraction grating. Additionally, a single‐crystal HKUST‐1 capacitive gas sensor with surface‐embedded electrodes that serves as a stable platform for the investigation of ethanol diffusion in the MOF pores is fabricated. The space‐confined fabrication strategy is promising for the integration of fragile MOF single crystals in various optical and electrical devices.

Integration atoms in octa- and tetrahedrical internodes of BCC crystals with a free surface

The physical properties of crystals are determined by their chemical nature, the structure of both the entire volume and the surface layer. The surface of a metal, ionic or covalent crystal and semiconductor can be considered as a special state of matter with its own chemistry and physics. The interest in the problem of solid state surfaces, in the science of surface, in the physics of thin films is stimulated by advances in solid state physics, technical innovations, opportunities to create new film materials with unique properties, the challenges of modern technology, the requirements of technology to create devices for computing technology and microelectronics. In this work the processes of redistribution of infiltration atoms along the surface and bulk inter-nodes are considered, the equilibrium distribution of infiltrated atoms on the surface and in the crystal volume, as well as the effect of external pressure on the surface and bulk distribution of infiltration atoms, are studied. Knowledge of the processes of redistribution of infiltration atoms along the inter-nodules of a crystal and of the reasons causing them may allow the purposeful formation of these processes for the purpose of obtaining certain physical characteristics of materials. The kinetics of inter-nodal rearrangement of infiltration atoms has been studied for metals and ordering alloys of various structures.

Recent Research Activities of Single-crystal Growth Groups in Korea

Single crystal growth research is the first step of experimental studies in condensed matter physics. Various new phenomena have been discovered in high-quality single crystalline materials, which was otherwise hidden in their polycrystalline form. In this article, we review recent research activities of single crystal growth groups in Korea. These activities cover a wide range of materials from epitaxial crystal of single-element metal to naturally-heterostructured crystals, which exhibit facinating properties and functionalites including strong oxidation resistance, superconductivity, multiferroics, quantum magnetism, and topological properties.

Will Polycrystalline Platinum Tip Sliding on a Gold(111) Surface Produce Regular Stick–Slip Friction?

Friction measurements by an atomic force microscope (AFM) frequently showed regular stick-slip friction signals with atomic-scale resolutions. Typically, for an AFM metal tip sliding on a metal crystal surface, the microstructure of the tip made from the thermally evaporated metal coating on a silicon cantilever was polycrystalline. Our detailed molecular dynamics(MD) simulations of a polycrystalline Pt tip (R = 10 nm in radius) sliding on an Au(111) surface revealed how the geometry of the polycrystalline tip took effect on the friction behavior at the contact interface. We found that the apex of the Pt tip with multiple grains near the edge of contact could induce severe plastic deformations of the gold substrate, leading to irregular stick-slip frictions upon sliding. Simulation results showed that in order to achieve a clear stick-slip friction signal with single atomic slips, the apex of the Pt tip must adopt a single crystalline protrusion without any neighboring grains involved in the metal contact. We showed that such a single crystalline protrusion, which presumably could be achieved during initial run-in or wear-out of high-energy Pt atoms in the neighboring grains, was passivated by a large number of gold atoms due to metal adhesion in the contact periphery. Using such a crystalline protrusion tip, we demonstrated that the stick-slip friction produced was very "tolerant" to the adhesion of a large number of gold atoms on the tip apex. We further showed that AFM tip mass used in MD simulations also played an important role in determining the transition between friction regimes, which could be well explained by the Prandtl-Tomlinson thermal activation model.