Atomic Arrangement Research Articles

Recent Development of Transition Metal‐based Amorphous Electrocatalysts for Water Splitting

AbstractElectrochemical water splitting, including the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), is a promising hydrogen production technology. However, in practice, the high overpotentials and sluggish reaction kinetics associated with the anode OER process are the major obstacles to the smooth progress of electrocatalytic water splitting. Amorphous electrocatalysts, a crucial family of functional materials, exhibit unexpected performance due to their special short‐range ordered and long‐range disordered atom arrangement, abundant defect sites and adjustable composition. To date, while numerous recent publications showcase promising results for transition metal‐based amorphous electrocatalysts, including amorphous metal phosphide and metal hydroxide electrocatalysts with remarkable HER and OER properties respectively, the utilization of single‐function HER or OER catalysts tends to augment system complexity for water electrolysis, thereby escalating the cost of hydrogen production. In this regard, amorphous HER/OER bifunctional electrocatalysts are desired. In this review, we summarize the recent development on transition metal‐based amorphous catalysts for electrochemical water splitting. The design strategies for constructing HER/OER bifunctional transition‐metal‐based amorphous electrocatalysts are highlighted here, also including the exploration of relationship between catalyst structures and their remarkably improved performance. Finally, the possibilities of amorphous bifunctional catalysts for practical industrial applications are evaluated and future research direction are suggested.

Preparation of Oriented Nanoporous Magnetite Films by a Template-Free Solution Process from Iron Oxyhydroxide Films

Nanoporous oxide films composed of nanocrystal assemblies with an aligned crystallographic orientation are key nanostructures for efficient interfacial reactions. However, a simple, template-free method for their formation remains a challenge. Layered metal hydroxide (LMH) films are a promising precursor for spontaneous formation of nanoporous oxide films.[1-4] LMHs have a layered structure comprising 2D sheets of edge-shared octahedral hydroxide, i.e., brucite structure, with or without interlayer anions and water molecules. Calcination of LMH results in dehydration, anion elimination, and volume shrinkage, leading to the spontaneous formation of nanoporous oxides.In this study, we have prepared nanoporous and ferrimagnetic magnetite (Fe3O4) films by using layered iron hydroxides, namely, green rust (GR), as a precursor. Generally, GR has a brucite-type structure containing Fe2+ and Fe3+ ions, and is highly susceptible to oxidation by oxygen in water and air, leading to the formation of iron oxyhydroxides (FeOOH). Here, GR films were electrochemically deposited on FTO substrates in an aqueous solution containing Fe2+ and NO3 − ions at room temperature. Drying the GR films in air resulted in the formation of two-type FeOOH films, depending on the electrodeposition condition. Characterization using X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, and FT-IR spectroscopy revealed that one is [010]-oriented γ-FeOOH films, and the other is [001]-oriented δ-FeOOH films. The obtained FeOOH films had a mille-feuille like morphology with 500–700 nm thickness. Heat treatment of these two-type FeOOH films under vacuum at 500 °C resulted in the formation of [110]- and [111]-oriented nanoporous Fe3O4 films. The obtained Fe3O4 films showed a ferrimagnetic behavior in VSM measurements and had a nanoporous structure comprising nanoparticles with 50–100 nm diameter.Finally, a possilble interpretation for the observed orientation relationships between the FeOOH and Fe3O4 was also discussed on the basis of pyrolysis intermediates of FeOOH and similarity in their atomic arrangements. References T. Shinagawa, M. Watanabe, T. Mori, J.-i. Tani, M. Chigane and M. Izaki, Inorg. Chem., 57, 13137 (2018).T. Shinagawa, M. Chigane and M. Izaki, ACS Omega, 6, 2312 (2021).T. Shinagawa, M. Chigane and M. Takahashi, Cryst. Growth Des., 22, 4122 (2022).T. Shinagawa, N. Kotobuki and A. Ohtaka, Nanoscale Adv., 5, 96 (2023). Figure 1

(Invited) Metallofullertubes or Metallofullerenes: Which Have We Isolated?

In our labs, we are isolating several novel carbon-metal endohedral molecules of unknown structures with rare-earth metals. In this presentation, we will discuss the feasibility of using chemical reactivity differences (Round 1) to obtain samples enriched in their presence. Next, using a multiple column HPLC approach for further resolution (Round 2), we have isolated and begun a preliminary characterization (e.g., UV-vis) for these pristine samples. We know their chemical formulas, but we do not yet know the structural arrangement of metal and carbon atoms. When sufficient quantities are obtained, we will pursue X-ray crystallography to address the following big question. Namely, do we have metals in tubes (metallofullertubes) or do we have metals in big balls (metallofullerenes). An objective of this presentation is to update and share with the fellow scientific community our most recent advances and progress in the research area of larger carbon cage structural housings (e.g., C96-C120).

Seeding as a Decisive Tool for Increasing Space-Time-Yields in the Preparation of High-Quality Cu/ZnO/ZrO2 Catalysts

Aging is one of the key steps in the preparation of highly active Cu/ZnO-based catalysts for use in the production of methanol. If certain pH and temperature specifications are met, an initially amorphous precipitate transforms into the crystalline precursor phase of zincian malachite, which is characterized by a periodic arrangement of Cu and Zn atoms and has proven advantageous for the quality of the final catalyst. However, aging generally takes between 30 min and multiple hours until the desired phase transformation is completed. With our study, we show that aging can be significantly accelerated by seeding the freshly precipitated suspension with already aged zincian malachite crystals: the necessary aging time was reduced by 41% for seeding mass fractions as low as 3 wt.% and from 83 min to less than 2 min for 30 wt.% seeds. No negative influence of seeding on the phase composition, specific surface area, molar metal ratios, or the morphology of the aged precursor could be identified. Consequently, the catalyst performance in the synthesis of methanol from CO2, as well as from a CO/CO2 mixture, was identical to a catalyst from an unseeded preparation and showed small advantages compared to a commercial sample. Thus, we conclude that seeding is a vital tool to accelerate the preparation of all Cu/Zn-based catalysts while maintaining product quality, presumably also on an industrial scale.

Roadmap for the Development of Transition Metal Oxide Cathodes for Rechargeable Zinc-Ion Batteries

Continued efforts towards the decarbonization of the power sector through an uptake of renewable energy generation, namely solar and wind, play a key role in the fight against climate change. However, due to their variable nature, the simultaneous implementation of energy storage solutions capable of ensuring a reliable delivery of energy at any time of day is of the utmost importance. Aqueous rechargeable zinc-ion batteries (RZIBs) are a promising technology for this end. Offering several advantages over lithium-ion batteries in terms of cost, environmental impact, and material abundance, the investment in RZIB research continues to grow. However, the realization of commercial RZIBs is currently hindered by the lack of cathode materials with adequate performance for long-term storage solutions. This is the case for manganese (e.g., MnO2, Mn2O3, Mn3O4) and vanadium (e.g., V2O5, VO2) based oxides, which exhibit considerable capacity fade during realistic charge and discharge times. While simple transition metal oxides (MyOx, M=transition metal) are one of the most studied classes of materials for RZIB cathodes, a literature survey shows that there are still many unexplored redox active elements and redox pairs which may be employed in next-generation RZIBs. Therefore, to accelerate the discovery of these novel cathode systems, we mapped the theoretical Zn intercalation potential for simple oxides from 12 different transition metals using Density Functional Theory (DFT) calculated thermodynamic properties. The screened elements were chosen upon considering their commercial availability, toxicity, price, and existence of previously reported structures containing zinc. During the present analysis, the feasibility of Zn intercalation for each system was accounted for by analyzing the atomic arrangement in the charged and discharged phases. Experimentally obtained Pourbaix Diagrams were also used to probe the electrochemical stability of the cathodes in aqueous solution, with the possibility of electrolyte degradation (oxygen or hydrogen evolution reaction) and competing reactions (metal dissolution or solid phase change) also considered. Experimental validation of the computationally predicted potentials was also done for select materials. The result for the 35+ redox pairs evaluated in this study provides a clear roadmap for the future development of RZIBs cathodes.

(Invited) Single-Atom Cu Catalysts for Electrochemical CO2 Reduction – Combining Theory, Synthesis and Electrochemical Characterization

Electrochemical CO2 reduction (CO2RR) is a leading sustainable approach for transforming atmospheric CO2 into valuable chemicals. This electrocatalytic process relies on a delicate balance of electron and proton transfer steps, resulting in the formation of diverse 1-carbon and some 2-carbon products, contingent on the surface properties. Extensive exploration of various transition metals for CO2RR has revealed that the binding strength of reaction intermediates on these metals significantly influences product selectivity. Notably, metals such as Au, Ag, Pd, Zn, Cd, Bi, Sn, and In, recognized for their activity in CO2RR, exhibit lower binding strengths for CO2 intermediates, leading to the predominant production of either HCOOH or CO as sole products. In contrast, Cu, with its moderate ability to bind CO2RR intermediates, yields multiple products during CO2RR, albeit with reduced selectivity [1]. Moreover, the overall efficiency of CO2 conversion is hampered by the simultaneous occurrence of the competing hydrogen evolution reaction (HER) at the potentials required for producing desired products. Thus, it is imperative to develop new, effective catalysts. Catalysts capable of suppressing HER while enhancing selectivity are essential for advancing the overall efficiency of CO2 conversion [2].Single-atom catalysts (SACs) are a relatively new class of materials that hold great promise due to their high specific activity and maximum atom utilization [3]. These catalysts often provide singular types of active sites, enhancing selectivity in reactions. However, the vast array of possible SACs, deployable on various supports, makes it impractical, if not possible, to use the traditional trial-and-error studies to yield high performing catalysts within reasonable timeframes. To navigate this complexity, theoretical investigations, especially DFT computations and machine learning techniques, have emerged as powerful tools. They can facilitate the identification of suitable catalyst structures and enable the precise engineering of atomic arrangement, therefore achieving targeted product formation from CO2 with enhanced conversion efficiency. Additionally, conventional synthesis methods suffer from various drawbacks, involving multiple steps, harsh conditions, and a lack of control over the metal site distribution in the carbon matrix, limiting the desired coordination structure [4, 5].Therefore, the work presented in this talk represents our combined experimental-theoretical effort. Specifically, Cu single atoms were strategically deposited onto defective carbon supports and systematically investigated for their performance as CO2RR electrocatalysts. These catalysts were inspired by DFT results showing how the product profile could be manipulated on catalyst surfaces, along with a prediction of the most likely products that would arise from the reaction.These catalysts were synthesized using a novel method denoted as switched solvent synthesis. This approach involves initially impregnating metals onto a carbon support, followed by switching the solvent from aqueous to an organic solvent with a higher dipole moment, and subsequently reducing the resulting mixture under an H2 environment. This innovative method offers notable advantages, enabling the efficient production of SACs in less time, at lower temperatures (~100-500 °C), and with high yields. In this study, Cu SACs were synthesized, and the influence of reaction parameters on the distribution of Cu metal atoms was systematically examined. The confirmation of SAC formation was achieved through various characterization techniques, including aberration-corrected STEM, XRD, and XPS.To assess the electrochemical activity and CO2 reduction abilities of the Cu SACs, electrochemical characterization techniques were employed under both He and CO2-saturated 0.1 M KHCO3 electrolytes. Furthermore, the product distribution and CO2 conversion efficiencies, including activity, stability, selectivity, and faradaic efficiency, of the Cu SACs were rigorously evaluated through electrolysis in a flow cell setup. Quantification of the results was performed using an integrated GC/MS instrument.

Understanding in-Plane Movement of Iridium in Proton Exchange Membrane Electrolyzer after Accelerated Stress Test

In the rapidly evolving field of clean energy, proton exchange membrane water electrolyzers (PEMWEs) stand at the forefront, heralding a new era of sustainable hydrogen fuel production. PEMWEs need to operate for at least 10 years and material degradation is a challenge that needs to be overcome. Here we use H2NEW accelerated stress (AST) protocol to degrade 5 cm2 PEMWE cell having low iridium loadings on the anode side. Using X-ray fluorescence (XRF) mapping, we first assessed the iridium distribution at the beginning of life (BOL) of the electrolyzer cell and then afterwards at the end of life (EOL). Regular electrical characterization with specific time intervals was conducted, such as collection of polarization curves, electrochemical impedance spectroscopy and cyclic voltammetry. Identical location was selected for iridium mapping. To complement XRF mapping, we also conducted X-ray diffraction (XRD) studies at the BOL and at the EOL. XRD reveals the crystalline structure and phase transitions of iridium, crucial for understanding how iridium’s atomic arrangement adapts to operational stresses. This comprehensive approach, combining XRF and XRD, aims to provide a multifaceted view of iridium’s behavior, distribution, and structural changes from the BOL to EOL. This research aims to unravel the behavior of iridium after AST, particularly whether it migrates into the ionomer, moves to the cathode, or undergoes other transformational shifts.Figure 1.micro-XRF map of iridium distribution on the anode of the PEMWE at the BOL. The map is 2 mm x 2 mm. Figure 1

Effect of Bi content and temperature on the shear mechanical properties of Fe-Bi nanocomposites: a molecular dynamics study

In this study, the effects of Bi content and temperature on the mechanical properties of Fe–Bi nanocomposites were investigated using molecular dynamics simulation. The research reveals that the nanocomposite’s shear strength reaches a peak of 3.785 GPa at a Bi content of 0.15%, attributed to the impediment of dislocation movement by twin boundaries during shearing, resulting in a dynamic ‘Hall–Petch’ effect and exceptional shear performance of the material. The abundant twinning induced around Bi phase inclusions introduces orientational disparities within the crystal, leading to grain misalignments, with dislocations in the grains slipping near the twin boundaries. In the nanocomposites, <100> dislocations merely act as initial sites for reactions, reducing their impact on the material’s strength and fracture behavior. The maximum stress decreases with increasing temperature while the magnitude of atomic transformations increases. The proportion of atoms at grain boundaries is higher at higher temperatures, and the arrangement of atoms at grain boundaries is more complex. At a temperature of 100 K, the dislocation density is highest with the smallest variation, forming a reinforced region within the material. The above results have significant implications for the design of environmentally friendly Bi-containing free-cutting steels.

Preparation of high purity phase (Bi, Pb)-2223 superconducting films by sol–gel method

In this work, a (Bi, Pb)2Sr2Ca2Cu3O10+δ ((Bi, Pb)-2223) solution with good film-forming capability and chemical stability was synthesized through using metal acetates as raw materials, acrylic acid as an additive, and anhydrous methanol as a solvent to adjust the sol formula. Subsequently, (Bi, Pb)-2223 thin films were fabricated on LaAlO3 (LAO) single-crystal substrates via dip-coating technology at different heat treatment temperatures, and the structures and properties of (Bi, Pb)-2223 films were characterized. It was found that when the sol stoichiometric ratio of Bi: Pb: Sr: Ca: Cu was controlled at 1.9: 0.35: 2: 2: 3 and the gel film was heat-treated at 860 °C and dwelled for 120 min in an mixed atmosphere of N2: O2 = 96: 4, the prepared thin film with a pure (Bi, Pb)-2223 superconducting phase exhibited excellent biaxial texture, a dense surface structure, and had a T c of 106 K and a ΔT c of 6 K. The microstructure analysis revealed a layered epitaxial growth of the film along the LAO substrate with a regular arrangement of atoms and a consistent interlayer spacing.

Molecular dynamics analysis of subsurface brittleness mechanism of nanocrystalline 3C-SiC rough friction surface

To study the effect of polycrystalline 3C-SiC rough friction surface on the mechanism of subsurface brittleness during nanocrystalline grinding. Initial grinding models of polycrystalline 3C-SiC and diamond abrasive grains on rough friction surfaces are developed using molecular dynamics methods and the Voronoi method for constructing polycrystalline abrasive grains. The processing mechanism of 3C-SiC is analyzed by post-processing methods such as dislocation defect analysis, atomic arrangement analysis and stress analysis. At 2.6 nm, "stress concentration" occurs between the abrasive particles and the workpiece, forming irregular force shapes. The larger the grain size, the smaller the crystal hardness, the greater the possibility of crystal fracture, and it is obvious in the crystal of larger grains. At 8 nm, the crystal breaks and creates vacancies. The roughness of the polycrystalline 3C-SiC friction surface and the cross-cutting mechanism between grains with grain boundaries are found to be effective in ameliorating the damage in the subsurface layer.

Amorphous Ru-based metallene with monometallic atomic interfaces for electrocatalytic hydrogen evolution in anion exchange membrane electrolyzer

Amorphous metallene is a prospective catalyst due to disordered atomic arrangement and abundant defects/edges. However, challenges persist in preparing amorphous metallene with atomic interface, primarily due to thermodynamic impediment of unconventional phase and difficulty in precise controlling of atomic interface. Here, we synthesized a new class of amorphous RuGa metallene (A-RuGa metallene) with abundant atomic interface by introducing trace atomic-dispersed Ga. The atomic interface between Ga-coordinated Ru and Ru0 achieves monometallic synergism during alkaline hydrogen evolution reaction. The turnover frequency value of A-RuGa0.06 metallene reaches 67 s−1 at −0.1 V vs. RHE. Meanwhile, the mass activity of A-RuGa0.06 metallene in anion exchange membrane electrolyzer reaches 5.2 A mgRu−1 at 2.0 V, firstly surpassing commercial Pt/C (1.0 A mgPt−1). The trace atomic dispersed Ga could change the local valence state of monometallic Ru, thus promoting water adsorption and dissociation, optimizing H* adsorption and accelerating H* transport at the atomic level.

Revaling the mechanism of microscopic kinking phenomena in Hf6Ta2O17 superstructures

As a promising candidate for a new-generation thermal barrier coating material, Hf6Ta2O17 is characterized by its unique long-period superstructures and excellent mechanical properties. In this study, the unique "kinking" phenomenon of the atomic arrangement in Hf6Ta2O17 crystals is directly visualized via high-resolution transmission electron microscopy for the first time. The evolution of the microstructure, and particularly the micro-mechanism of the "kinking" phenomenon, have been further explored by first-principles calculations. The study suggests that this phenomenon is primarily triggered by the rotation of the polyhedral structure, resulting from the partial elongation or shortening of the Ta-O bond length. These structural alterations are believed to directly influence the macroscopic mechanical properties and can improve the tensile properties of the Hf6Ta2O17 crystals. The findings of this study provide an important microscopic perspective for understanding the strain-induced crystal structure transformation. The quantitative analysis of the strengths of Ta-O and Hf-O bonds in different coordination polyhedra reveals the electronic structure changes behind the crystal structure transition, thus providing a new theoretical basis for an in-depth understanding of the behavior of crystals under the external stress.

Electrons redistribution of palladium-copper nanoclusters boosting the direct oxidation of methane to methanol

The direct oxidation of methane to methanol (DOMM) at mild conditions is an enormous attractive yet highly challenging, which is known as the “Holy Grail” reaction. In this work, we prepare the PdxCuy NCs supported on mesoporous sulfur-carbon materials and investigate their catalytic DOMM performance. The Pd14Cu1 NCs exhibits the excellent DOMM performance with the productivity of 34.3 mmol g−1 h−1 and the selectivity of 92.3 % at 150 °C when H2/O2 as active oxygen species, which was obviously superior to other PdCu catalysts. The enhanced performance of Pd14Cu1 NCs in DOMM is attributed to the non-crystalline atomic arrangement of tiny cluster structures and the synergistic electronic effect between Pd and Cu atoms, which can reduce the desorption temperature for methane, improve the in-situ generation of H2O2, and provide more active oxygen. The time-resolved in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) demonstrated that a radical-involved reaction pathway on Pd14Cu1 NC. This work provides the understanding for synergistic effect dual metallic and helps to design highly efficient and selective catalysts for the direct oxidation of CH4.

Atomistic descriptor optimization using complementary Euclidean and geodesic distance information

Descriptors are physically-inspired, symmetry-preserving schemes for representing atomistic systems that play a central role in the construction of models of potential energy surfaces. Although physical intuition can be flexibly encoded into descriptor schemes, they are generally ultimately guided only by the spatial or topological arrangement of atoms in the system. However, since interatomic potential models aim to capture the variation of the potential energy with respect to atomic configurations, it is conceivable that they would benefit from descriptor schemes that implicitly encode both structural and energetic information rather than structural information alone. Therefore, we propose a novel approach for the optimisation of descriptors based on encoding information about geodesic distances along potential energy manifolds into the hyperparameters of commonly used descriptor schemes. To accomplish this, we combine two ideas: (1) a differential-geometric approach for the fast estimation of approximate geodesic distances [Zhu et al., J. Chem. Phys. 150, 164103 (2019)]; and (2) an information-theoretic evaluation metric – information imbalance – for measuring the shared information between two distance measures [Glielmo et al. PNAS Nexus, 1, 1 (2022)]. Using three example molecules – ethanol, malonaldehyde, and aspirin – from the MD22 dataset, we first show that Euclidean (in Cartesian coordinates) and geodesic distances are inequivalent distance measures, indicating the need for updated ground-truth distance measures that go beyond the Euclidean (or, more broadly, spatial) distance. We then utilize a Bayesian optimisation framework to show that descriptors (in this case, atom-centred symmetry functions) can be optimized to maximally express a certain type of distance information, such as Euclidean or geodesic information. We also show that modifying the Bayesian optimisation algorithm to minimise a combined objective function – the sum of the descriptor ↔ Euclidean and descriptor ↔ geodesic information imbalances – can yield descriptors that not only optimally express both Euclidean and geodesic distance information simultaneously, but in fact resolve substantial disagreements between descriptors optimized to encode only one type of distance measure. We discuss the relevance of our approach to the design of more physically rich and informative descriptors that can encode useful, alternative information about molecular systems.

A catalyst family of high-entropy alloy atomic layers with square atomic arrangements comprising iron- and platinum-group metals.

We report a catalyst family of high-entropy alloy (HEA) atomic layers having three elements from iron-group metals (IGMs) and two elements from platinum-group metals (PGMs). Ten distinct quinary compositions of IGM-PGM-HEA with precisely controlled square atomic arrangements are used to explore their impact on hydrogen evolution reaction (HER) and hydrogen oxidation reaction (HOR). The PtRuFeCoNi atomic layers perform enhanced catalytic activity and durability toward HER and HOR when benchmarked against the other IGM-PGM-HEA and commercial Pt/C catalysts. Operando synchrotron x-ray absorption spectroscopy and density functional theory simulations confirm the cocktail effect arising from the multielement composition. This effect optimizes hydrogen-adsorption free energy and contributes to the remarkable catalytic activity observed in PtRuFeCoNi. In situ electron microscopy captures the phase transformation of metastable PtRuFeCoNi during the annealing process. They transform from random atomic mixing (25°C), to ordered L10 (300°C) and L12 (400°C) intermetallic, and finally phase-separated states (500°C).

Rotational Spectroscopy as a Tool to Characterize Sweet Taste: The Study of Dulcin.

According to old theories of sweetness, the perception of sweet substances is closely linked to the arrangement of atoms within them. To assess the validity of these theories, we conducted an analysis of the structure of the artificial sweetener dulcin for the first time, utilizing microwave spectroscopy and a laser ablation source. These techniques have enabled the identification of two conformers, which are stabilized by an intramolecular hydrogen bond between the amino group and the phenyl ring. The observed conformations were examined in light of the Shallenberger-Acree-Kier molecular theory of sweet taste, and they align with the hypothesized criteria. Furthermore, the study illustrates how conformational relaxation can alter the equilibrium conformational distribution, resulting in the absence of certain conformers in the conformational landscape.

Amorphous Nanomaterials: Emerging Catalysts for Electrochemical Carbon Dioxide Reduction

AbstractIn the past decades, the rapid depletion of non‐renewable energy sources has caused growing energy crisis and increasing emissions of carbon dioxide (CO2), which aggravates global warming and catastrophic climate change. Electrocatalysis is regarded as an effective method for consuming atmospheric CO2 and simultaneously alleviating the energy problem by converting CO2 into high value‐added chemicals. Amorphous nanomaterials with long‐range disordered structures possess abundant highly unsaturated atomic sites and dangling bonds on their surfaces, thus providing a large number of active sites, and show unique electronic structures compared to their crystalline counterparts due to the distinct atomic arrangements. Therefore, amorphous nanomaterials are recently demonstrated as highly efficient catalysts for diverse electrocatalytic reactions, including electrocatalytic CO2 reduction reaction (CO2RR). Here the rational synthesis and electrocatalytic performance of newly emerging amorphous nanomaterials will be outlined for electrocatalytic CO2RR. Importantly, the intrinsic merits of these amorphous catalysts in CO2RR processes will be summarized and highlighted. Finally, these perspectives on the remaining challenges and some potential future directions in this emerging field will also be provided.

VASE: A High-Entropy Alloy Short-Range Order Structural Descriptor for Machine Learning.

The short-range order (SRO) structure in high-entropy alloys (HEAs) is closely associated with many properties, which can be studied through density functional theory (DFT) calculations. Atomic-scale modeling and calculations require substantial computational resources, and machine learning can provide rapid estimations of DFT results. To describe SRO information in HEAs, a new descriptor based on Voronoi Analysis and Shannon Entropy (VASE) is proposed. Based on Voronoi analysis, the Shannon entropy is introduced to directly characterize atomic spatial arrangement information except for composition and atomic interactions, which is necessary for describing the disorder atomic occupancy in HEAs. The new descriptor is used for predicting the formation energy of FeCoNiAlTiCu system based on machine learning model, which is more accurate than other descriptors (Coulomb matrices, partial radial distribution functions, and Voronoi analysis). Moreover, the model trained based on VASE descriptors exhibits the best predictive performance for unrelaxed structures (24.06 meV/atom). The introduction of Shannon entropy provides an effective representation of atomic arrangement information in HEAs, which is a powerful tool for investigating the SRO phenomena.

A Fundamental Correlative Spectroscopic Study on Li1‐xNiO2 and NaNiO2

AbstractThe intricate relationship between local atomic arrangements and electronic states significantly influences the electrochemical properties of Li‐ion battery cathode materials. Despite decades of investigation, a consensus regarding the local atomic and electronic structure of LiNiO2 remains elusive. This ambiguity stems from the potential distortion of Ni sites, either via Jahn‐Teller (JT) distortion or bond disproportionation (BD), complicating the understanding of the charge compensation mechanism involving Ni and O. This study compares the structures of LiNiO2 and NaNiO2, a JT system, using an innovative approach that integrates bulk spectroscopy techniques on standardized interoperable samples for enhanced reliability. While X‐r and theoretical calculations fail to differentiate between the proposed scenarios, Raman spectroscopy highlights local structural distinctions between monoclinic NaNiO2 and rhombohedral LiNiO2. HAXPES confirms various formal oxidation states for Ni, supported by RIXS data indicating 3d8 states, emphasizing negative charge transfer from Ni and some bond disproportionation in LiNiO2. Regarding charge compensation, XRS and RIXS suggest oxygen hole involvement in redox activity, whereas Raman spectroscopy does not detect molecular oxygen. This comprehensive spectroscopic analysis highlights the importance of correlative characterization workflows in elucidating complex structural‐electrochemical relationships.

Nearly close-packed atomic arrangements in BaTi2O5 glass

Recent advancements in glass synthesis have led to the creation of novel oxide glasses without tetrahedral corner-sharing networks. Of particular interest are glasses with high atomic packing densities, showcasing improved functionalities. Conventional analyses revealed the presence of not only four-coordinated polyhedra but also five- or six-coordinated polyhedra, which are connected via corner-sharing, edge-sharing, or face-sharing linkages. This study adapted the reduced atomic arrangement (RAA) method to analyze densely packed oxide glasses. The RAA method revealed a near-close-packed structure within a 10 Å range throughout BaTi2O5 glass, with Ba2+ and O2− ions arranged accordingly. Moreover, the structural model derived from relaxing the closest-packed arrangement via molecular dynamics simulations faithfully replicated the X-ray diffraction data. These findings suggest that minor deviations from the closest-packed atomic arrangement can initiate glass formation without corner-sharing tetrahedral networks. The RAA method proves highly effective in understanding glass formation mechanisms in unconventional oxide glasses.