Atomic Size Research Articles

One-pot fabrication of high-entropy heterostructure cathode materials with excellent anti-poisoning properties in solid oxide fuel cells

Degradation of cathode performance in solid oxide fuel cells (SOFCs), which is poisoned by atmospheric CO2 and volatilized Cr from steel connecting plates, is a key factor limiting the long-term stable operation. In this work, high entropy heterostructure La0.5Ba0.5Fe0.2Co0.2Ni0.2Cu0.2Mn0.2O3-δ@Ba2CuO3 (HE-LBF@BCO) is designed and prepared by the one-pot method to improve the anti-poisoning ability of the electrode against CO2 and Cr. Meanwhile, the Ba2CuO3 (BCO) heterostructure formed by self-assembly using atomic size effect improves the electrochemical performance. The peak power density with HE-LBF@BCO cathode reaches 789 mW cm−2 at 800 °C with the polarization impedance of 0.34 Ω cm2. To further extend the three-phase interface and enhance oxygen catalytic activity, for HE-LBF@BCO-Gd0.1Ce0.9O2-δ(GDC) composite cathode, the peak power density reaches 789 mW cm−2 and the polarization impedance decreases to 0.16 Ω cm2 at 800 °C, exhibiting a brilliant application potential of the high entropy cathode. More importantly, HE-LBF@BCO-GDC shows an outstanding stability both in CO2 and Cr-containing atmosphere. After testing in Cr-containing atmosphere at 0.8V, the current density of the single cell with HE-LBF@BCO-GDC cathode decreases from 250.86 to 208.64 mA cm−2 at 700 °C. The results confirm the design of high-entropy heterojunction electrode materials provides a new strategy to address the enhancement of SOFC performance.

Structure, Synthetic Pathway, and Properties of Metastable Phosphorus Carbide, P4C3.

Due to electronegativity (EN) differences, changing from C3N4 to P4C3 is not as trivial as simply replacing nitrogen by phosphorus in the C3N4 structure. Hence, the nonexistent P4C3 phase is nominally the higher-homologue analogue of the well-known C3N4, but its structure and properties are practically unknown for fundamental reasons. Here we predict, by means of an extensive structure search, three energetically favorable yet metastable P4C3 phases adopting space groups P1̅, Cm, and Cmmm, followed by designing their synthetic routes. Different from the planar structural motifs of C3N4, P4C3 is likely to adopt various "puckered" (as regards the P atoms) forms, mainly related to the EN difference between nitrogen and phosphorus, the difference in atomic size, and also less favorable sp orbital mixing for phosphorus related to primogenic repulsion; hence, the P substructures are characterized by single and fractional P-P bonds with rectangular/linear motifs or those resembling simple-cubic P, including multicenter bonding as a function of the large electron count. As regards the carbon substructures, infinite polyacetylene-like motifs, carbon dimers, and infinite chains of cyclopentadienyl-like and polyphenyl-like units are predicted, with C-C bond orders larger than one. Band structure analyses indicate the metallic character of these three phases. The P1̅ polymorph exhibits a Dirac cone, whereas the Cmmm phase, being composed of metallic "phosphorene" units and infinite polyphenyl units, might show potential in applications, e.g., battery electrodes. Moreover, the monolayer of the P1̅ polymorph should be easy to exfoliate and exhibit a large anisotropy with regard to mechanical and electronic properties. The synthesis of P4C3 defining a new class of IV3V4 compounds should be attempted due to its predicted structural and physicochemical properties.

Mitigating Band Tailing in Kesterite Solar Absorbers: Ab Initio Quantum Dynamics.

Open-circuit voltage deficits are limiting factors in kesterite solar cells. Addressing this issue by suppressing band tailing and nonradiative charge recombination is essential for enhancing the performance. We employ ab initio nonadiabatic molecular dynamics to elucidate the origin of band tailing and charge losses and propose a mitigation strategy. The simulations show that Cu-Zn disorder, associated with antisite defect clusters [CuZn+ZnCu], is a significant source of band tailing in kesterites, as evidenced by the much larger Urbach energy in disordered than ordered kesterites. Cu-Zn disorder gives rise to new sulfur-centered coordination polyhedra, increases structural inhomogeneity, changes electrostatic potential at sulfur centers, and shifts the S(3p) orbital energy. Differences in the S(3p)/Cu(3d) and S(3p)/Sn(5s) hybridization strengths and the S(3p) orbital energy shift reduce the band gap by 0.37 eV. Furthermore, Cu-Zn disorder enhances vibrational motion of sulfur anions and surrounding cations, increasing band gap fluctuations by 15 meV. The stronger electron-phonon interactions reduce charge carrier lifetimes and limit the kesterite solar cell efficiency. Partial substitution of Zn with Cd facilitates structural ordering and significantly suppresses band tailing, particularly in disordered systems. The improvement can be attributed to the larger atomic radius and mass of Cd, which weakens bonding around the anion, suppresses S-related vibrations within the covalent tetrahedra, and reduces nonadiabatic coupling, thereby increasing charge carrier lifetimes. The reported results establish the key influence of cation disorder on band tailing and reduced charge carrier lifetimes in kesterites and highlight cation disorder engineering as a strategy to achieve high-efficiency kesterite solar cells.

Local compressive strain-induced anti-corrosion over isolated Ru-decorated Co3O4 for efficient acidic oxygen evolution

Enhancing corrosion resistance is essential for developing efficient electrocatalysts for acidic oxygen evolution reaction (OER). Herein, we report the strategic manipulation of the local compressive strain to reinforce the anti-corrosion properties of the non-precious Co3O4 support. The incorporation of Ru single atoms, larger in atomic size than Co, into the Co3O4 lattice (Ru-Co3O4), triggers localized strain compression and lattice distortion on the Co-O lattice. A comprehensive exploration of the correlation between this specific local compressive strain and electrocatalytic performance is conducted through experimental and theoretical analyses. The presence of the localized strain in Ru-Co3O4 is confirmed by operando X-ray absorption studies and supported by quantum calculations. This local strain, presented in a shortened Co-O bond length, enhances the anti-corrosion properties of Co3O4 by suppressing metal dissolutions. Consequently, Ru-Co3O4 shows satisfactory stability, maintaining OER for over 400 hours at 30 mA cm−2 with minimal decay. This study demonstrates the potential of the local strain effect in fortifying catalyst stability for acidic OER and beyond.

Optical and surface properties of Schiff base ligands and Cu(II) and Co(II) complexes

Objectives. To study the transition of electrons in 1,2-phenyl(4’-carboxy)benzylidene Schiff base ligand and transition metal ions, optical properties, as well as the surface chemistry of supported transition metals using diffuse reflectance spectroscopy (DRS); to study the roughness and morphology of the Schiff base ligand and its complexes using atomic force microscopy (AFM).Methods. DRS, AFM, and Fourier-transform infrared spectroscopy instruments were used to identify electron transitions, optical properties, and surface morphology in Schiff base ligands and their complexes.Results. The DRS revealed the d–d transitions and charge transfer shifts of all compounds, and helped identify the structure of the ligand. One of the optical properties studied was the energy gap calculation of the ligand and its complexes. The copper complex exhibited more semiconducting behavior with surface morphology properties such as surface roughness parameters lower than those of the ligand and the cobalt complex. This can be attributed to the smaller size of the copper atom, as well as lower electron transitions compared to the cobalt complex and the square planar bonding shape.Conclusions. In Schiff base ligands, the reflectance spectrum bands reveal three electron transitions: n→π*, π→π*, and σ→σ* transitions. In cobalt complexes, four transitions are indicated: 4A2(F)→4T1(F), 4A2(F)→4T1(P), charge transfer bands, and tetrahedral geometry. Copper complexes exhibit three transitions: 2B1g→2A1g, 2B1g→2Eg, and charge transfer bands, with a square planar geometry for their structure. The energy gap calculations were 2.42, 2.29, and 2.30 eV, respectively. In the case of the SH ligands, copper complexes, and cobalt complexes, all compounds exhibited semiconductor properties. However, the complexes displayed increased conductivity due to the influence of the metal and coordination structure.

Effects of Lu-doping on the magnetic behaviour and ordering of (Ho[formula omitted]Lu[formula omitted])2Fe2Si2C

We have investigated the effects of Lu substitution on the magnetic behaviour and ordering of (Ho1−xLux)2Fe2Si2C (x = 0.32 and 0.46) by high-resolution neutron powder diffraction, magnetisation and specific heat over the temperature range 2 to 300 K. Our study has establised that the antiferromagnetic (AFM) state is weakened upon Lu substitution and that the Néel temperature TN shifts towards lower temperature with increasing Lu content. The replacement of the magnetic Ho3+ ion by the non-magnetic Lu3+ ion of smaller atomic radius, leads to a modification of the crystal field levels, as indicated by the specific heat measurements. Neutron diffraction data analysis reveals that the magnetic structure of undoped Ho2Fe2Si2C, which exhibits a commensurate, antiferromagnetic ordering of the Ho sublattice along the b-axis with a propagation vector k = [0, 0, 12], is maintained in the Lu-doped (Ho1−xLux)2Fe2Si2C compounds.

Design and fabrication of multiphase TiVCrZrW films with superior wear resistance and corrosion resistance

High entropy alloys (HEAs) have the potential to overcome the conflict between hardness and toughness by incorporating dual-phase or multiphase structures. Under unbalanced magnetron sputtering, HEA films with large atomic size differences tend to form non-monophasic structures. In this study, based on a phase diagram calculation simulation, a multiphase TiVCrZrW film with deposition temperature-induced phase separation was successfully designed. Interestingly, the TiVCrZrW film deposited at 600 °C exhibited a multiphase structure including a double body-centered cubic (BCC) phase and Laves phase by spinodal decomposition, realizing a balance between hardness and toughness. The tribological experiments showed that the multiphase TiVCrZrW film provided superior wear resistance, with a minimum wear rate of 2.63 × 10−6 mm3/(N·m). The electrochemical experiment demonstrated the outstanding corrosion resistance of the multiphase TiVCrZrW film, and the corrosive solution was effectively inhibited by the ZrO2 and Cr2O3 oxides passive film formed on the surface. According to the results of this study, TiVCrZrW protective films have a wide range of potential applications in various fields of marine engineering.

Effects of Scandium doping on the deuterium absorption and desorption behavior of titanium films

Understanding the effects of Scandium (Sc) on the hydrogen absorption and desorption capabilities and the underlying mechanisms within Ti–Sc alloys is crucial for their applications as hydrogen storage materials. In this study, we explore the influence of Sc on deuterium (D) behavior in Titanium (Ti) films through a combination of experimental characterization and theoretical simulations. The Sc-doped Ti films with different Sc ratio were prepared using magnetron sputtering. Our findings indicate that Sc doping raises the D absorption temperature from 350 °C to 500 °C, and the Sc-doped Ti deuteride films exhibit higher apparent activation energies and temperatures for D desorption. Results from both experiments and DFT calculations indicate that these phenomena are attributed to the atomic size effect, in which the larger Sc atoms reduce the Ti–H spacing, thereby strengthening the interaction between the adjacent Ti atoms and H atoms. The enhanced interaction presents a greater challenge for H atom diffusion within α-Ti and complicates the dissociation of TiH2. This study provides a vital theoretical and experimental basis for understanding the effects of Sc doping on the hydrogen absorption and desorption properties in titanium alloys.

CALCULATION OF ELECTRONIC PROPERTIES OF LiBX3 (B = Pb AND Sn; X = Br, Cl AND I) CUBIC PHASE BY DENSITY FUNCTIONAL THEORY

Perovskite solar cells utilize perovskite as the active material to convert sunlight into electrical energy. Perovskite is a compound with a crystal structure of ABX₃, where A and B are cations, and X is an anion, usually a halide. Research continues to find perovskites with high efficiency. This efficiency is related to the electronic structure, which can be analyzed using Density Functional Theory (DFT). In this study, the electronic structure of cubic phase LiBX₃ perovskites (B = Pb and Sn; X = Br, Cl, and I) is investigated using Quantum ESPRESSO software. Various parameters such as cut-off energy, k-points, and lattice constants were modified to obtain optimal values. From the optimization results, the band gap, DOS, and PDOS values for the six perovskites were obtained. The resulting band gap energy (Eg) are LiPbBr₃ at 1,71 eV, LiPbCl₃ at 1,87 eV, LiPbI₃ at 1,43 eV, LiSnBr₃ at 0,51 eV, LiSnCl₃ at 0,65 eV, and LiSnI₃ at 0,28 eV. These results show that the band gap energy values increase with the change in atomic radius from Sn to Pb and decrease with the change in atomic radius from Cl, Br to I. The electronic structure calculations of LiBX₃ (B = Pb and Sn; X = Br, Cl, and I) show semiconductor properties that have the potential to be used as light-absorbing materials in perovskite solar cells. This study states that LiBX₃ has great potential in solar cell applications and offers a deep understanding of the relationship between crystal structure and its electronic properties.

Tailoring ZrWNb-Based Refractory High Entropy Alloys: A Multidirectional Characterization Through Elemental, Physical, Thermodynamic, and Nuclear Radiation Attenuation Properties

This study explores the development and characterization of 18 novel ZrWNb[(X)(Y)] (where XY are Hf, Ta, Mo, V, Ti) refractory high entropy alloys (RHEAs) designed to enhance mechanical robustness, thermodynamic stability, and radiation shielding effectiveness. Through a rigorous analysis, we evaluated the elastic modulus, entropy, and enthalpy of mixing, atomic size difference, valence electron concentration, and the omega parameter to understand the alloys’ phase behavior and structural integrity. Our findings revealed a broad range of elastic modulus values, indicating diverse mechanical adaptability suitable for high-stress applications. The thermodynamic assessment highlighted several RHEAs with favorable phase stability, particularly ZrWNbTaHf and ZrWNbTiTaHf, which are poised for high-performance usage due to their balanced mixing entropy and enthalpy. This study also benchmarks the RHEAs against conventional alloys, with sample R1 exhibiting the lowest fast neutron effective removal cross section, underscoring its superior neutron shielding capabilities. Additionally, R1 demonstrated exceptional photon attenuation, as evidenced by its competitive half-value layer performance across an extensive energy spectrum. Collectively, these results position R1 as a standout candidate, offering a significant advancement in materials science for applications demanding stringent radiation shielding, such as in nuclear reactor environments and space exploration.

Prediction of the thermal-physical properties of amorphous nickel alloys Ni2B, Ni44Nb56, Ni62Nb38 according to component data

The replacement of traditional materials with amorphous alloys and the operation of products made from them are determined by the structural, temporal and temperature stability of disordered environments. In particular, the thermal stability of an amorphous alloy directly depends on its thermophysical characteristics. Therefore, the article demonstrates the applicability of the rule of mixing components and the use of their data on thermophysical properties in the crystalline state to evaluate similar characteristics of alloys from the metal – metalloid and transition metal – transition metal groups in the amorphous phase. It has been established that for the transition metal – transition metal group, the assessment of the heat capacity of amorphous nickel alloys gives a better approximation to the experimentally established values than for an alloy from the metal – metalloid group. The reasons for the discrepancy between the assessment and experimental data for an alloy from the metal – metalloid group are possibly the covalency of the atomic bonds in contrast to the metallic bond for alloys from the transition metal – transition metal group, the smaller size of the metalloid atoms, its greater mobility and the effect on the refinement of alloy grains. The possibility of an amorphous alloy inheriting some properties of one of the components is indicated, which requires experimental verification.

Phase stability of solid solution La1-xRxRh3B (R = Gd, Lu and Sc) compounds with cubic anti-perovskite type structure

We have investigated the solid solution range of single phase La1-xRxRh3B (R = Gd, Lu and Sc) compounds with a cubic anti-perovskite type structure. The behaviors of lattice parameters, hardness, and thermogravimetry–differential thermal analysis (TG-DTA) were also investigated. The cubic anti-perovskite phase exists over the entire composition range x from 0.0 to 1.0 for all La-Gd, La-Lu and La-Sc systems. Both the lattice parameters and the hardness in all La-Gd, La-Lu and La-Sc systems show a linear dependence on the degree of the substitution x of La atom. The results of TG-DTA measurements indicate that oxidation of the compounds in air begins at about 500–600 K. The mixed phases of RBO3, R2O3 and Rh are identified as oxidized products around x = 0.4 to 0.6 composition. The oxidation onset temperature, and weight gains due to the oxidation depend on the degree of substitution x. The behavior of crystallographic and physical/chemical properties in the present compounds La1-xRxRh3B strongly depend on the atomic size of the rare-earth atoms that form the cubic framework.

Effect of carbon on microstructure and mechanical properties of TiZrNb0.5V0.5 lightweight refractory high entropy alloy

The single-phase body-centered cubic TiZrNb0.5V0.5 lightweight refractory high entropy alloy exhibits good plasticity but poor strength. Therefore, C is added to this alloy to enhance its strength and improve its mechanical properties in this paper. The influence of varying C content on the microstructure, phase composition, and mechanical behavior of TiZrNb0.5V0.5C x RHEAs is investigated in detail. The results indicate that C addition leads to the dissolution of alloying dendrites and induces the formation of the FCC – MC carbides phase. The carbide volume fraction increases in proportion to the carbon content, thereby enhancing the alloy's yield strength and hardness. The yield strength increases by 36%, while the hardness increases by 39%. The physical parameters of the alloy are analyzed, which reveals that the introduction of C increases the alloy's electronegativity and atomic radius difference, thus promoting the formation of carbides.

Synthesis of π-Extended [1.1]Paracyclophanes, [1.1][n]PCP (n=2, 3, and 4), and Their Through-Space Conjugation.

[1.1][n]Paracyclophanes ([1.1][n]PCPs) (3) with n=2, 3, and 4, which consist of two [n]paraphenylene units connected by methylene bridges, were synthesized using short synthetic pathways with good overall yields. Single-crystal X-ray diffraction analyses reveal that the paraphenylene unit in 3 is bent, resulting in an elliptic core structure of 3. The facing bridgehead carbons of the paraphenylene units are separated by a distance much shorter than the sum of the van der Waals radii of sp2-carbon atoms. UV-vis absorption spectra, fluorescence spectra, electrochemical measurements, and theoretical calculations were used to demonstrate the presence of through-space (TS) conjugation in 3. Furthermore, host-guest complex formation between 3D (n=3) and tetracyanoquinodimethane in the solid state was revealed.

Optimizing strength-ductility synergy of the solid-solution Ti50–ZrVNbCr MEAs via coordinately adjusting VEC and lattice constant

In this study, a series of Ti50–ZrVNbCr alloys were designed under with the constant atomic radius mismatch. It was suggested that valence electron concentration (VEC) and lattice constant, which evolve oppositely in the series of the Ti50–ZrVNbCr alloys, jointly influence the mechanical properties. Based on modeling, the evolution of ductility and yield strength of the designed alloys was predicted. Ductility was predicted to be superior in the VEC range from 4.22 to 4.25, with the lattice constant correspondently ranging from 3.340 Å to 3.334 Å. The optimization of strength-ductility synergy was discussed in terms of coordinately adjusting VEC and lattice constant. The experimental results were quite consistent with the prediction results, showing that the alloy with the VEC value of 4.25 and the lattice constant of 3.334 Å, which consisted of 50 at.%Ti, 28.1 at.%Zr, 9.4 at.%V, 9.4 at.%Nb, and 3.1 at.%Cr, possessed the best ductility and superior strength-ductility synergy.

Bending-induced enhanced spatial separation of dopants and long-lived conventional nanoribbon p-n junctions.

The spatial separation of dopants is crucial in extending the lifetime of nanoribbon p-n junctions, which is traditionally realized via van der Waals heterostructures at a high cost. In this study, we employ atomistic quantum mechanical simulations to demonstrate that a simple in-plane bending deformation can lead to an enhanced doping preference in conventional nanoribbons. Dopants with larger atomic sizes than those of host atoms tend to reside on the tensile side close to the outermost edge of the bent nanoribbons, while dopants with smaller atomic sizes than those of host atoms tend to reside on the compressive side close to the innermost edge of the bent nanoribbons. We also show that this doping preference induces an enhanced spatial separation of n-type and p-type dopants with different atomic sizes. As conventional nanoribbons are easier to synthesize and cost-effective, our results provide a pathway for modulating dopant distribution and designing long-lived nanoribbon p-n junctions via inhomogeneous strain engineering.

High-throughput screening of the potential alloying elements for high-strength Mg alloys based on solid-solution strengthening

Abstract 49 types of alloy atomic dopants and their effects on the doping stability and micro-mechanical behaviour of magnesium matrix were investigated using density functional theory and high throughput first-principles calculations. Geometry optimization was performed for each doping system, and the ability of atom doping into the magnesium matrix was assessed based on the doping energy and atomic radius. Results show that the transition metal elements have negative or near negative doping energy, especially for the elements with a radius that similar to Mg. The micro-mechanical properties of the doping system were evaluated by computing the fracture energy and theoretical tensile stress. Through a screening on the doping stability and strengthening effect of 49 types of alloy atoms, a set of elements (Re, Os, Ir, Tc and W, etc.) are screened out that could strengthen the magnesium matrix with a good doping stability. The high throughput screen results serve as a theoretical guide for the selection of appropriate alloy elements for designing the high-strength magnesium alloys in the regime of solid solution strengthening effects.

Metal single-atom interaction with graphitic C3N4 surface based on density functional theory calculations and linear regression analysis

This paper discusses the adsorption of metal single-atoms (SAs) on graphitic C3N4 (gCN) multilayered surface models based on density functional theory (DFT) calculations. We systematically searched stable adsorption sites on gCN and showed that the cavity site is preferred for metal SAs. We also discussed the usefulness of several descriptors, such as the distance between the SA and gCN, charge donation (electron transfer), and atomic radius, for evaluating the SA adsorption energy, based on the linear regression method. In addition, the most stable adsorption energy for fifth- and sixth-row metals can be predicted using only the “group” descriptor of the periodic table. The group descriptor is closely related to the atomic radius, and hence the stability of fifth- and sixth-row metals is determined from the fit between the SA radius and the gCN cavity size. The study findings facilitate the development of various metal-dopant techniques for gCN-based applications.

Specifics of Al substitution into boron carbide: A DFT study

Boron carbide (B4C), known for its hardness and low density, is prone to local amorphization under high non-hydrostatic loads, limiting its applications. Aluminum doping is promising due to aluminum's atomic size, fitting into the B4C crystal lattice, particularly the intericosahedra chain, potentially reducing amorphization. This work uses first-principles calculations to study aluminum placement in B4C. We examine the potential for Al substitution in the icosahedron and intericosahedra chain, identifying possible locations. Results show that aluminum can't replace atoms in the icosahedron, but substituting one central atom in the intericosahedra chain with aluminum is energetically favorable and likely changes the chain configuration to an angular one. Additionally, aluminum can substitute one carbon in the (C-B-C) chain of B12(C-B-C) boron carbide. Comparative analysis suggests these configurations may coexist. Our study offers a theoretical model that can guide future experimental efforts and provides valuable insights into the structural specifics of aluminum-doped boron carbide.

Insights of the Multimode Orientation-Dependent Initial Oxidation of Aluminum by First-Principles Theory Calculations.

A fundamental understanding of the oxidation mechanisms of aluminum (Al) alloys is of great importance for its applications in corrosion, catalysis, sensors, etc. In this work, we systematically investigated the first-stage oxidation behaviors of three low-index Al facets with O coverage up to two monolayers (ML) by using density-functional theory (DFT). The large negative adsorption energies indicated favorable oxidation on all three facets. However, distinctive structural and electronic changes induced by the adsorption of oxygen have led to different oxidation modes. More specifically, the oxidation process proceeded by "intercalating" into the subsurface region along the (111) plane out of the (110) facet with spontaneous O ingress into (110) far below one ML, as revealed by the electron density distribution, whereas the oxide ad-layer grew in a "layer-by-layer" mode on Al(111) and (001) facets. Moreover, various Al-O complexes with different atomic coordination numbers (CN), configurations, and sizes may be indicators of the tendency of an Al surface to be oxidized. Besides, the oxide phases formed on (111)/(001) and (110) assembled the Al-O bond distribution within α-Al2O3 and γ-Al2O3, respectively.