Corner Site Research Articles

Atomically L12 ordered (PtHf)x(NiTi)100-x/CNT as bifunctional catalysts for hydrogen evolution reaction and methanol oxidation reaction with high activity and durability

Instead of a sluggish oxygen evolution reaction (OER), a methanol oxidation reaction (MOR) is combined with a hydrogen evolution reaction (HER) for efficient hydrogen production. Here, by data-driven and density functional theory (DFT) calculation, we establish a combined theoretical–and experimental strategy for designing L12 ordered structures. Based on L12-PtNiTi, Hf element is added. Hf atoms occupy the α-site (face-centered site of FCC) with Pt. Ni atoms occupy the β-site (corner site of FCC) with Ti. The (PtHf)x(NiTi)100-x nano-alloy maintains L12 structure, enhancing intrinsic anti-poisonous performance and reducing Pt content. L12 (PtHf)50(NiTi)50/CNT exhibits an overpotential of 19 mV for HER and a mass activity of 4.725 A/mgPt for MOR in acidic electrolyte. For coupling HER with MOR, the working voltage is merely 0.55 V at 10 mA cm−2. It is demonstrated by DFT calculations that ordered (PtHf)50(NiTi)50/CNT has superior electrocatalytic performance attributed to smaller H adsorption energy, stronger OH binding energy and weaker CO adsorption energy.

Designing antiperovskite derivatives via atomic-position splitting for photovoltaic applications.

Due to the success of halide perovskites in the photovoltaic field, halide perovskite-derived semiconductors have also been widely studied for optoelectronic applications. However, the photovoltaic performance of these perovskite derivatives still lags significantly behind their perovskite counterparts, mainly due to deficiencies at the B-site or X-site of the derivatives, which disrupt the connectivity of the key [BX6] octahedra units. Herein, we developed a class of antiperovskite-derived materials with the formula , achieved by splitting the A anion, originally at the corner site of the cubic antiperovskite structure, into three edge-centered sites. This structural transformation maintains the three-dimensional octahedral framework. The thermodynamic stability, dynamical stability, and band gaps of 80 compounds were calculated using first-principles calculations. Based on criteria including stability and electronic properties, we identified 9 promising antiperovskite derivatives for further evaluation of their photovoltaic performance. Notably, the calculated theoretical maximum efficiencies of Ba3BiI3, Ba3SbI3, and Ba3BiBr3 all exceed 24.5%, which is comparable to that of CH3NH3PbI3 solar cells. Interpretable machine learning analysis was further carried out to identify critical physical descriptors influencing thermodynamic stability and band gap. Our work provides a novel approach for designing high performance perovskite-type structure-inspired semiconductors with potential for optoelectronic applications.

Quantum state transfer on 1-dimensional and 2-dimensional topological Heisenberg spin models

The geometrical significance of winding number is used to study the topological characteristics of a single-excitation Heisenberg XY spin model represented by the Su–Schrieffer–Heeger (SSH) model. Due to the presence of topological edge states, the quantum state may be conveyed from the first site to the last site with a high degree of fidelity. Also examined is a Heisenberg XY model on the kagome lattice. In the topological phase of the kagome lattice, the three corner states are not affected by the Dzyaloshinskii–Moriya (DM) interactions. For the kagome lattice with and without the DM interactions, the state of a spin on one corner site can be transferred to the other two corner sites in various ways during the topological phase. The quantum state transfer (QST) for the XY model on the kagome lattice without the DM interactions is symmetrical and can only produce a three-body entangled state. In contrast, the QST for the XY model on the kagome lattice with the DM interactions is in an asymmetrical form, similar to one-way propagation, and it can produce both product states and three-body entangled states.

Unveiling the Co effect on the temporal evolution kinetics of γ′ phase in Ni–Al–Co model superalloys via CALPHAD–informed phase field simulations

Co is a valuable γ solid solution strengthening element in nickel-based superalloys that improves their microstructure and creep resistance. However, the impact of Co additions on the kinetics of γ′ precipitation remains controversial. In this study, we conducted CALPHAD-informed phase field simulations to quantitatively analyze the γ′ precipitation process in Ni–Al–Co model superalloys and uncover the Co effect on the temporal evolution kinetics of the γ′ phase. Our simulations revealed that the γ′ coarsening rate initially decreases, then increases at 1173 K with increasing Co content, a change that can be attributed to the competition between the γ/γ′ lattice misfit and interdiffusion coefficients. Although Co is a γ-stabilized element, our calculations and previous experiments show an anomalous increase in γ′ volume fraction with increasing Co concentration, which is linked to variations in elemental partitioning behaviors between the γ matrix and γ′ phase. Furthermore, the unique partitioning behavior of Ni suggests partial replacement of Al atoms at the corner site of γ′-Ni3(Al, Ni) sublattice by Ni atoms. Our research offers a new perspective on the effect of Co concentration on the kinetics of γ′ precipitation in Ni–Al–Co model superalloys and outlines a guideline for designing novel multicomponent superalloys with superior microstructural stability.

Edge and corner superconductivity in a two-dimensional topological model

We consider a two-dimensional generalization of the Su-Schrieffer-Heeger model which is known to possess a nontrivial topological band structure. For this model, which is characterized by a single parameter, the hopping ratio $0\ensuremath{\le}r\ensuremath{\le}1$, the inhomogeneous superconducting phases induced by an attractive-$U$ Hubbard interaction are studied using mean-field theory. We show, analytically and by numerical diagonalization, that in lattices with open boundaries, phases with enhanced superconducting order on the corners or the edges can appear, depending on the filling. For finite samples at half filling, the corner site superconducting transition temperature can be much larger than that of the bulk. A novel proximity effect thus arises for ${T}_{c,\mathrm{bulk}}<T<{T}_{c,\mathrm{corner}}$, in which the corner site creates a nonzero tail of the superconducting order in the bulk. We show that such tails should be observable for a range of $r$ and $U$ values.

Stochastic finite fault modeling of Mw 6.4 earthquake along Indo-Burmese arc and site classification of its seismic recording station

This study simulates the strong ground motion of an earthquake having magnitude 6.4 occurred on 4 February 2011 in Indo-Burmese Arc (IBA). This earthquake recorded on seven seismic recording stations namely Jowai, Jorhat, Sibsagar, Nagaon, Guwahati, Cooch Bihar and Kokhrajhar. Also, estimation of site class performed to observe the site effects of recording stations in this study. The simulation performed on the basis of revised stochastic finite fault model with dynamic corner frequency and site class for the seismic recording station where the earthquake recorded has been estimated by using Horizontal to Vertical Spectral Ratio (HVSR) technique because modeling and simulation of ground motion majorly depend upon the recorded ground motion as well as site effects, where earthquake has been recorded. The revised well known finite source simulation program (EXSIM) used in this study becomes efficient in providing the results for small magnitude earthquake occurred at large distance. The average HVSR curves plotted for all the recording stations, providing peak frequency for all 7 sites. It is observed from the present work that simulated time histories as far as primary attributes, for example, Fourier spectra, Peak ground acceleration (PGA), Response spectra, Predominant frequency are in close concurrence with the recorded ones. The predominant frequency (fpeak) obtained from HVSR technique has been validated from existing literature for the estimation of site class for seismic recording stations. The fpeak determines the average shear wave velocity (Vs30) at depth of 30 ​m of overburden thickness which varies from 200 ​m/s to 1600 ​m/s according to Program for Excellence in Strong Motion Studies (PESMOS). Whereas, National Earthquake Hazard Reduction Program (NEHRP) provision consider the site class for Vs30 below 180 ​m/s. Due its wide range of site characterization, it has been adopted globally. Therefore, in this study, the site class obtained has been compared with the site classification scheme recommended by PESMOS, NEHRP provisions and previous literature. However, the ground motion parameters and the soil classification of the earthquake recording stations for the IBA region has not been explored yet even after seeing its severity in the past decades. Productive representation of present earthquake gives the confidence to understand and evaluate seismic danger at various parts of Indo- Burmese region from tremors of various sizes. In this study it is proposed that PESMOS site classification data should be revised because it covers wide range of soil types just into three (A, B and C type) class.

Microkinetic simulations of acetylene(acetylene-d2) hydrogenation(deuteration) on Ag nanoparticles

The semi-hydrogenation(deuteration) of alkynes plays an essential role in high-value chemical production, and the reaction mechanism between H and D remains elusive. In this work, advanced microkinetic modeling is combined with the energetics from the first principles calculation to investigate the activity and selectivity of acetylene hydrogenation (acetylene-d2 deuteration) on Ag nanoparticles. By constructing a polyhedral model, it can be found that the olefin production on Ag nanoparticles converged when the size was at the diameter of 6 nm. Furthermore, it is found that the effective production rates are contributed by Ag(100) and Ag55 (corner site). The temperature considerably affects the free reaction energy (ΔG) between hydrogenation and deuteration. Consistent with the experiment, our kinetic simulations indicate that hydrogenation gives rise to a reaction rate approximately 3 times larger than the TOF of deuteration.

C2H2 selective hydrogenation over the single-atom Pt1/Cu catalysts: Unraveling the role of Pt active site type and its coordination environment in regulating catalytic performance

To unravel the role of active site type and its coordination environment in regulating catalytic performance, C2H2 selective hydrogenation over a series of single-atom Pt1/Cu catalysts was fully investigated using DFT calculations and microkinetic modeling. Four types of Pt active site, including the defect, step, corner, and terrace sites with the generalized coordination number (GCN) from 2.5 to 7.5, are examined. Our results indicate that Pt1/Cu catalysts with four types of active sites favor gas phase C2H4 formation in C2H2 hydrogenation process. C2H4 activity has an inverted volcanic-type curve relationship with d-band center and GCN of Pt active site. For the polymerization process, the corner and terrace sites with larger GCN values could prevent green oil. The screened PtGCN3.0 catalyst with corner site exhibits better C2H4 selectivity and activity and prevents green oil. Hence, tuning the type and GCN value of Pt active site well regulate C2H4 activity and selectivity, as well as catalyst stability, which provide useful structure information to rationally design Pt-based catalysts in C2H2 selective hydrogenation.

Kinetic Monte Carlo Simulation Studies of the Shape of Islands on Close-Packed Surfaces

Kinetic Monte Carlo simulations are used to study processes that affect the shape of islands during growth of close-packed surfaces. The difference in adatom binding energy at the two types of edges and the relative height of diffusion barriers together with the incident flux and temperature determine which of the two types of edges dominates. This in turn affects strongly whether the crystal grows layer-by-layer or forms three-dimensional islands. Several features of the energy landscape that affect the island shape are illustrated. An unexpected edge nucleation effect involving addimer formation near a corner where edges meet can strongly affect the shape of small islands especially at low flux. Since the barrier for an adatom to exit a corner site to an edge site is lowered by such dimer formation, the overall activation energy for transport from an edge with low diffusion barrier to an edge with high diffusion barrier is reduced. As a result, small islands mainly have edges for which the diffusion barrier is lower. However, for large islands, the adatom is more likely to find a kink on the edge that has smaller diffusion barrier so large islands mainly has edges where the diffusion barrier is higher.

Spin-Glass-Like Behavior in Mn3Ga0.3Sn0.7N Compound

The magnetic transition, thermal property, and the distance of Mn–Mn of Mn3Ga0.3Sn0.7N compound with the Sn element substitution of Ga in Mn3GaN compounds were investigated. Magnetic measurements indicate that the existence of spin glass system at high temperature (502 K) in Mn3Ga0.3Sn0.7N compound may be attributed to competing antiferromagnetic (AFM) and ferromagnetic (FM) interactions due to the doped Sn inducing ferromagnetic orders in Mn3GaN and the partially random Sn substitute Ga at a corner site of the lattice. It is not clear how much role the pure Sn power, which is not doped into Ga site completely, played in inducing the magnetic characteristic. This finding will be helpful to reveal the mechanism of the antiperovskites’ intriguing physics properties and to develop more smart materials.

Circuit quantum electrodynamics simulator of the two-dimensional Su-Schrieffer-Heeger model: higher-order topological phase transition induced by a continuously varying magnetic field.

Higher-order topological insulator (HOTI) occupies an important position in topological band theory due to its exotic bulk-edge correspondence. Recently, it has been predicted that external magnetic field can induce novel topological phases in 2D HOTIs. However, up to now the theoretical description is still incomplete and the experimental realization is still lacking. Here we proposed a superconducting quantum circuit simulator of 2D Su-Schriffer-Heeger lattice, which is one of the most celebrated HOTI models, and investigate consequently the influence of the continuously varying magnetic field. By using the parametric conversion coupling method, we can establish in principle the time- and site-resolved tunable hopping constants in the proposed architecture, thus providing an ideal platform for investigating the higher-order topological phase transitions induced by continuously varying magnetic field. Our numerical calculation further shows that the higher-order topology of the lattice, which manifests itself through the existence of the zero energy corner modes, exhibit exotic and rich dependence on the imposed magnetic field and the inhomogeneous hopping strength. To probe the proposed magnetic-field-induced topological phase transition, we study the response of the lattice to the corner site pumping in the steady state limit, with results implying that the predicted topological phase boundaries can be unambiguously identified by the measurement of the corner sites and their few neighbors. Requiring only current level of technology, our scheme can be readily tested in experiment and may pave an alternative way towards the future investigation of HOTIs under various mechanisms including magnetic field, disorder, and strong correlation.

Metallic Nitride and Carbide Perovskites: History and Prospects

Energy-level diagrams for cubic metallic Fe4N and Mn4N were proposed by Goodenough in the late 1960s. Fe4N is ferromagnetic, but Mn4N is ferrimagnetic with a large moment on Mnc at the cube corner site and a much smaller antiparallel contribution from Mnf at the three face-centre sites. Neutron diffraction revealed noncollinear ferrimagnetism with no compensation where the Mnf moments form 120° triangular antiferromagnetic sublattices but are tilted out of the kagome (111) planes to give the small net sublattice moment. A rich variety of magnetic ordering exists in the ternary Mn3−xM′xN metallic perovskites. Partial substitution of nonmagnetic M′ on Mnc sites leads to a tunable ferrimagnetic compensation point. Two possible antiferromagnetic modes in the kagome planes are a topological Γ4g mode, and a nontopological Γ5g mode where the in-plane components of the Mnf spins lie, respectively, perpendicular and parallel to the edges if the triangles in the kagome planes . Interest in the metallic perovskites has revived with the availability of high-quality thin films that facilitate measurements of magneto-transport properties, strain effects and spin wave velocity. The range of magnetic structures, magnetotransport, magnetocaloric and magnetovolume effects is exceptionally large. The topological ferrimagnets exhibit large anomalous Hall effects. The magnetism is compared with materials where N is replaced by C.

A DFT investigation on the hydrodesulfurization mechanism of 4,6-dimethyldibenzothiophene over different Ni-Mo-S active sites via different direct desulfurization pathways

The computational method based on the first principle of numerical atomic functions of density functional theory (DFT) was established to investigate the effects of ferromagnetism for the auxiliary Ni species on the direct desulfurization (DDS) mechanism of 4,6-dimethydibenzothiophene (4,6-DMDBT) hydrodesulfurization via two different reaction paths on both the corner active site and the edge active site. It is less likely for 4,6-DMDBT undergoing the DDS reaction via both paths on the Ni-Mo-S edge active sites without considering the ferromagnetism due to the relative activation energy needed either for the cleavage of the first C–S bond or for the cleavage of the second C–S bond. However, 4,6-DMDBT can undergo the DDS reaction via the Path 2 DDS mechanism in which the cleavage of the first C–S bond is the reaction rate control step. On the corner site, 4,6-DMDBT inclines to undergo DDS via both the promoted paths and the cleavage of the first C–S bond is the reaction rate control step, the ferromagnetism of the Ni species lowered the activation energy for the reaction rate control step by approximately 4.8 kJ·mol−1. The activation energy for the cleavage of the second C–S bond in the Path 1 DDS mechanism reduced from about 217.92 kJ·mol−1 to 112.32 kJ·mol−1 after taking the ferromagnetism of Ni species into account. Thus, the ferromagnetism of Ni species has a crucial effect on the DDS of 4,6-DMDBT over both the corner active site and the Ni-Mo-S edge active site and should not be neglected.

Changes in physicochemical properties of old stabilized sand dunes due to atmospheric sediments and diversity of clay minerals in a dry area

Abstract Sand dune hills were stabilized by petroleum mulch and biological methods in southwest Iran. The present study aims to identify the effects of these landscapes on airborne dust entrapment in five regions, including uphill (UH), downhill (DH), and canopy tree positions after 54 years. These locations were at different distances from dust sources and prevailing winds. The results revealed that salinity in the study areas showed the following trend: canopy > UH > DH. Silt particles were entrapped in the corner 4 times greater than the inner areas. Moreover, silt deposition flux ranged from 54 gm−2 yr−1 (the minimum) in the inner site (Al-Baji) to 207.4 g m−2 yr−1 (the maximum) in the corner site (SG). Unlike silt, clay flux was maximal in both inner (124.4) and corner (123.4) locations due to the movement of fine materials in high elevations. The total deposition of materials (silt + clay) was maximal (330.8) and minimal (155.6 g m−2 yr−1) in the corner and inner sites, respectively. The clay mineralogy indicated that these hills had two groups of minerals. Primary minerals, i.e. carbonates and silicates, were inherited from parent materials. Secondary minerals were identified in surface soil, and peaks in the subsurface were very weak. Wind sediments added these clays to the surfaces. The abundance of these clays showed the following trend: palygorskite > smectite > vermiculite. It was found that these areas do not disturb the atmosphere by dust and play an important role in air purification because the surface roughness of these hills was promoted by artificially planted trees.

Dielectric response of BaTiO[formula omitted] electronic states under AC fields via microsecond time-resolved X-ray absorption spectroscopy

For the first time, the dielectric response of a BaTiO3 thin film under an AC electric field is investigated using microsecond time-resolved X-ray absorption spectroscopy at the Ti K-edge in order to clarify correlated contributions of each constituent atom on the electronic states. Intensities of the pre-edge eg peak and shoulder structure just below the main edge increase with an increase in the amplitude of the applied electric field, whereas that of the main peak decreases in an opposite manner. Based on the multiple scattering theory, the increase and decrease of the eg and main peaks are simulated for different Ti off-center displacements. Our results indicate that these spectral features reflect the inter- and intra-atomic hybridization of Ti 3d with O 2p and Ti 4p, respectively. In contrast, the shoulder structure is not affected by changes in the Ti off-center displacement but is susceptible to the effect of the corner site Ba ions. This is the first experimental verification of electronic contribution of Ba to polarization reversal.

Effects of Cr content on compositional evolution and precipitation kinetics of γ′ phase in Ni–Al–Cr alloy: 2D phase-field simulation

The two-dimensional phase-field simulation coupled with the sublattice model is utilized to simulate the γ′ precipitation in Ni-12 Al-x Cr at.% (x = 8, 9, 10) alloys aged at 1073 K for 831 h. The compositional evolution of Cr and Al, and the precipitation kinetics of γ′ phase are studied. At the nucleation and growth stage, the concentration distribution of Cr and Al is characterized by an Al enrichment and Cr depletion at the γ/γ′ interface. As Cr content increases from 8 to 10 at.%, the partition ratio of Al and Ni into γ′ phase is promoted, and the equilibrium volume fraction of γ′ phase is increased, while the Al and Ni atoms at the corner site of L12-Ni3(Al, Cr) sublattice are replaced by Cr atoms partly. Besides, the coarsening rate constants of steady-state coarsening (166.2 < t < 831 h) are less than that of growth and coarsening stage (4.2 < t < 50.0 h), the increased Cr content promotes the coarsening of γ′ phase, and the average radius of γ′ phase obeys the time exponent 1/3 well for a high Cr content alloy.

Molecular Nanowire Bonding to Epitaxial Single-Layer MoS2 by an On-Surface Ullmann Coupling Reaction.

Lateral heterostructures consisting of 2D transition metal dichalcogenides (TMDCs) directly interfaced with molecular networks or nanowires can be used to construct new hybrid materials with interesting electronic and spintronic properties. However, chemical methods for selective and controllable bond formation between 2D materials and organic molecular networks need to be developed. As a demonstration of a self-assembled organic nanowire-TMDC system, a method to link and interconnect epitaxial single-layer MoS2 flakes with organic molecules is demonstrated. Whereas pristine epitaxial single-layer MoS2 has no affinity for molecular attachment, it is found that single-layer MoS2 will selectively bind the organic molecule 2,8-dibromodibenzothiophene (DBDBT) in a surface-assisted Ullmann coupling reaction when the MoS2 has been activated by pre-exposing it to hydrogen. Atom-resolved scanning tunneling microscopy (STM) imaging is used to analyze the bonding of the nanowires, and thereby it is revealed that selective bonding takes place on a specific S atom at the corner site between the two types of zig-zag edges available in a hexagonal single layer MoS2 sheet. The method reported here successfully combining synthesis of epitaxial TMDCs and Ullmann coupling reactions on surfaces may open up new synthesis routes for 2D organic-TMDC hybrid materials.

Áthangszerelt finálé - Hard Rock Hotel | Budapest, Nagymező utca

Architects: László SZÁSZ and Erzsébet HAJNÁDY Following the established business model of the Hard Rock company design concepts are handled by their local franchise partner. Here the decision was made to respect the existing building's elevations, whilst adding a three storey high golden crown that responds to the location, Nagymező Utca's, Broadway like ambitions. To lift a corner site architecturally with a bold, traditionally, out of context statement. This approach completes the problem of a poorly massed streetscape whilst adding a taste of Rock 'n' Roll rebellion.

EPR Spectroscopy of Iron- and Nickel-Doped [ZnAl]-Layered Double Hydroxides: Modeling Active Sites in Heterogeneous Water Oxidation Catalysts.

Iron-doped nickel layered double hydroxides (LDHs) are among the most active heterogeneous water oxidation catalysts. Due to interspin interactions, however, the high density of magnetic centers results in line-broadening in magnetic resonance spectra. As a result, gaining atomic-level insight into the catalytic mechanism via electron paramagnetic resonance (EPR) is not generally possible. To circumvent spin-spin broadening, iron and nickel atoms were doped into nonmagnetic [ZnAl]-LDH materials and the coordination environments of the isolated Fe(III) and Ni(II) sites were characterized. Multifrequency EPR spectroscopy identified two distinct Fe(III) sites (S = 5/2) in [Fe:ZnAl]-LDH. Changes in zero field splitting (ZFS) were induced by dehydration of the material, revealing that one of the Fe(III) sites was solvent-exposed (i.e., at an edge, corner, or defect site). These solvent-exposed sites featured an axial ZFS of 0.21 cm-1 when hydrated. The ZFS increased dramatically upon dehydration (to -1.5 cm-1), owing to lower symmetry and a decrease in the coordination number of iron. The ZFS of the other ("inert") Fe(III) site maintained an axial ZFS of 0.19-0.20 cm-1 under both hydrated and dehydrated conditions. We observed a similar effect in [Ni:ZnAl]-LDH materials; notably, Ni(II) (S = 1) atoms displayed a single, small ZFS (±0.30 cm-1) in hydrated material, whereas two distinct Ni(II) ZFS values (±0.30 and ±1.1 cm-1) were observed in the dehydrated samples. Although the magnetically dilute materials were not active catalysts, the identification of model sites in which the coordination environments of iron and nickel were particularly labile (e.g., by simple vacuum drying) is an important step toward identifying sites in which the coordination number may drop spontaneously in water, a probable mechanism of water oxidation in functional materials.

The Effect of Pulse Electrodeposition of Bismuth on Electrochemical Reduction of Carbon Dioxide to Formate

Efficient electrochemical reduction of CO2 to formate is demonstrated by fabricating Bi nanoflake with pulse electrodeposition. The effect of pulse voltage on morphology of the Bi nanoflake and electrochemical property was investigated. The pulse voltage of 80 mVAg/AgCl with six pulse cycles successfully produces ultrathin Bi nanoflakes. The finite-element-based simulation shows that the two-dimensional geometry with large lateral dimensions and ultrathin thickness can localize a strong electric field at the corner site of the flakes, resulting in facilitating efficient reduction of CO2 to formate. As a result, formate Faradaic efficiency of the Bi nanoflakes showed over 90% at − 0.8 VRHE. Also, the formate production rate reached 69 µmol/cm2/h at − 0.8 VRHE. The pulse electrodeposition provides highly dense and uniform and tailored nanostructures in the large area without the requirements of high vacuum or high temperatures process.