Substitutional Solid Solutions Research Articles

More about the BaO(BaCO3)–Lu2O3–CuO system

The phase diagram of the BaO(BaCO3)–Lu2O3–CuO system was built at 900°C. It comprises of 8 single-phase, 15 two-phase, and 8 three-phase regions. The boundary oxide systems Lu2O3–CuO and BaO–CuO contain the phases Lu2Cu2O5 (structure type Ho2Cu2O5, Pearson symbol oP36, space group Pna21, a = 10.702(1), b = 3.412(1), c = 12.360(1) Å, RB = 0.076) and Ba44Cu45O90 (own structure type, cI400, Im-3m, a = 18.294(3) Å, RB = 0.114), whereas in the Lu2O3–BaO(BaCO3) system the oxide-carbonate Ba3Lu2[CO3]O5 (Ba3Yb2[CO3]O5, tP26, P4/mmm, a = 4.322(1), c = 11.862(2) Å, RB = 0.107) was identified under the conditions of the experiment. Two quaternary oxides were observed. The structure of BaLu2CuO5 was confirmed (BaY2CuO5, oP36, Pnma), whereas the structure of the phase with approximate composition Ba3LuCu2O6.5 still needs to be established. The electrochemical properties of BaLu2CuO5 as cathode material in Li-ion batteries were investigated. The existence of a (in part) substitutional solid solution BaLu2CuO5:Li was confirmed by the decrease of the unit-cell volume (–0.11 %). No traces of the formation of a phase with YBCO-type structure were detected at 900°C.

Investigation of Sr-substituted Ba1-xSrx(Zn1/3Nb2/3)O3 complex perovskites: structural, electrical and electrochemical properties

Herein we report the structural, dielectric and electrochemical properties of Ba1-xSrx(Zn1/3Nb2/3)O3 (BSZN, 0 ≤ x ≤1) solid solution synthesised by solid-state reaction. A complete substitutional solid solution was obtained, wherein the BSZN cubic perovskites of the space group of Pmm were obtained at x ≤ 0.6 while the pseudo-cubic phases were discernible at x > 0.6. The nano-sized crystallites, as determined by both Scherrer and Williamson-Hall analyses, supported the claim of large polyhedral grains of 0.1 to 0.3 μm by FE-SEM. Both ε′ and tan δ were found to vary consistently with increasing dopant concentration, except for an anomalous observation for the composition, x = 0.6 with the lowest tan δ of 0.0783 and the highest ε′ of 27.5. Such phenomenon could be attributed to the combined effects of larger grain size, higher relative density and stronger polarisation per molar volume. The impedance analysis revealed that these BSZN perovskites were of the negative temperature coefficient of resistance (NTCR) type. The combined plots of imaginary modulus (M″) and impedance (Z″) against frequency showed the short-range movement of localised charge carriers, suggesting a non-Debye-type relaxation process.

Effect of Ti/Ta ratio on the microstructure and mechanical properties of Hf20Mo15Nb25Ta20-xTi20+x refractory high-entropy alloys

The limited deformation capacity at room temperature remains a significant challenge in refractory high-entropy alloys (RHEAs). In this study, the fine-grained Hf20Mo15Nb25Ta20-xTi20+x (x = 0, 5, 10, 15) alloys were prepared by mechanical alloying and subsequent spark plasma sintering (SPS), based on precise component regulation. The impact of altering the Ti/Ta ratio (R, R = (20+x)/(20-x)) on the pre-alloyed powders and the as-sintered alloys were investigated. An increase in R-value led to larger powder particle sizes and lower powder yields, which was attributed to the improvement in the plasticity of the pre-alloyed powders. After SPS sintering, the as-sintered alloys were comprised of two BCC solid solution matrices and nanoscale precipitated phases. As the R-value increases, the stability of the microstructure decreases slightly, while the yield strength shows a slight improvement, and the plastic strain experiences a relatively significant enhancement. The as-sintered Hf20Mo15Nb25Ta20-xTi20+x alloys all exhibited an excellent balance of strength and plasticity. Theoretical calculations revealed that the yield strength of the alloys was the result of the combined effect of several strengthening mechanisms, predominantly substitutional solid solution strengthening. Furthermore, a systematic discussion was conducted on the reasons for the improvement in the plasticity of the as-sintered alloys. This study presents an effective approach to enhancing the room temperature deformation capacity of RHEAs, thereby facilitating their broader application.

Densification, phase composition, microstructure and properties of spark plasma sintered La0.6Ce0.3Pr0.1B6 bulks

This paper studied the densification, phase composition, microstructure and properties of polycrystalline La0.6Ce0.3Pr0.1B6 bulks prepared by SPS. The dense specimen (98.9 % in relative density) with the average grain size of 15.46 μm has been determined to be a CsCl-type single-phase substitutional solid solution without any impurities or other secondary phases. The homogenous elemental distributions of La, Ce and Pr have been confirmed by both microscale and nanoscale. The room temperature (RT) Vickers hardness (Hv), indentation fracture toughness (KIC) and flexure strength of the dense specimen have been measured to be 23.0 GPa, 2.04 MPa m1/2 and 305.1 MPa, respectively. The Berkovich hardness (HB) and elastic modulus (E) of the dense specimen have been measured to be 30.0 GPa and 376.0 GPa, respectively, by nanoindentation tests at a maximum load of 40 mN. In comparison with the polycrystalline LaB6 bulk, the lower work function Φ of 2.64 eV evaluated by UPS and the larger thermionic emission current densities measured at the same operating condition suggest that the polycrystalline La0.6Ce0.3Pr0.1B6 bulk is a superior-performance thermionic cathode material.

Excitation energy transfer in gadolinium tantalum niobates activated with Eu3+ and Tb3+

Series of gadolinium tantalum niobates activated with Eu3+ and Tb3+ ((Gd1-y-zEuyTbz)NbxTa1-xO4 (x = 0, 0.3, 1; y = 0.6; z = 0.06; 0.15; 0.3)) were obtained for the first time. The formation of substitutional solid solutions was demonstrated. The obtained ceramic solid solutions had a monoclinic structure with I2/a space group. Electron probe microanalysis, photoluminescence (PL) and cathodoluminescence (CL) were used for studies of gadolinium tantalates and tantalum niobates series activated with Eu3++Tb3+. CL and PL spectra, concentration dependences of CL intensity and decay times, as well as excitation spectra for 5D0-7F2 Eu3+ and 5D4-7F5 Tb3+ bands were analyzed. It was shown for the first time that both energy transfer from Tb3+ to Eu3+ ions, and a reverse process – energy transfer from Eu3+ to Tb3+ ions are observed. This reverse process led to a decrease in CL intensity and decay times of europium bands in the presence of terbium 3+ in these materials. Presumably this phenomenon is influenced by anti-Stokes luminescence. This is confirmed by the dependences of anti-Stokes luminescence probability on temperature and excitation density.

Efficient Catalysts Based on Substitutional Solid Solutions and Palladium Intermetallic Compounds for the Selective Hydrogenation of Acetylene to Ethylene

Efficient Catalysts Based on Substitutional Solid Solutions and Palladium Intermetallic Compounds for the Selective Hydrogenation of Acetylene to Ethylene

Phase composition and microstructure of intermetallic alloys obtained using electron-beam additive manufacturing

The paper investigates the microstructure and phase composition of nickel- and aluminum-based intermetallic alloys obtained using two-wire electron-beam additive manufacturing (EBAM). Relevance of the research is related to the widespread use of intermetallic alloys based on nickel and aluminum (mainly Ni3Al) in various high-temperature applications and the need to use modern production methods when creating machine parts and mechanisms from these alloys. Using EBAM, the billets from intermetallic alloys with different ratios of the content of main components were obtained. Change in concentrations of the basic elements was carried out varying the ratio of feed rates of nickel and aluminum wires during additive manufacturing in the range from 1:1 to 3:1, respectively. The results of microscopic studies of the obtained alloys showed that, regardless of nickel content, the obtained alloys are characterized by a large–crystalline structure with grain sizes in the range of 100 – 300 μm for alloys with a component ratio of 1:1 and 150 – 400 μm for alloys with a component ratio of 2:1 and 3:1. At the same time, the alloy with an equal content of base components is characterized by more uniform grain and microstructure compared to those with high content of Ni. By changing the concentration ratio of the components, phase composition of the resulting billet can be purposefully controlled. In the case of an “equiatomic” content of the base components in the alloy, a NiAl-based compound with a small phase content based on the intermetallides Ni3Al5 and Ni3Al is formed. At high concent­rations of nickel, the intermetallic Ni3Al phase is formed, and at a component ratio of 3:1, structure of the resulting billet consists mainly of Ni3Al phase and the γ solid substitutional solution based on nickel. The paper demonstrates the possibility of direct production of intermetallic alloys with a given phase composition during electron-beam additive manufacturing.

Data-Driven Material Exploration of High Conductive Fluorides By Multi-Element Substitution

Barium fluoride (BaF2) has a fluorite-type structure and is attracting high attention as a solid electrolyte material for fluoride ion batteries that can be used under high voltage. Previous research has reported that the ionic conductivity increases by 4 to 5 orders of magnitude by partially replacing Ba in BaF2 with La. This indicates that elemental substitution is effective in improving the ionic conductivity of BaF2. However, single element substitution only explore much limited experimental space in elements, so that it should be difficult to discover innovative conductive compositions. By replacing various elements at the same time, the experimental space can be largely expanded and the possibility of finding the optimal composition increases. But, the combination numbers of multi-element substituted compositions are much over 10000, and exhaustive exploration of them is unrealistic. Therefore, we aimed to efficiently search for multi-element substitution compositions with high conductivity by creating a material-conductivity correlated exploring system under data-driven approach using large number of fluoride material database. The purpose of this research was to discover solid solution compositions in the multi-element substituted fluorides and understanding of the relationship between substitutional elements and solid solution formation.Approximately 20 types of multi-element substitution composition candidates were initially picked up using the D-optimal design (Dopt). The target compositions were synthesized to collect their XRD data. Next, we extracted the "number of peaks" from the XRD data as a feature values to express the degree of solid solution in the sample. Furthermore, we made a regression model with the element types and addition ratios as explanatory variables and the "number of peaks" as the objective variable. Using the regression model, approximately 20 candidate were predicted to form solid solution, in which we called as data-driven design of experiments (DOE) approach. Finally, the materials were actually prepared according to the proposal in DOE. The identification results were projected using the principal component analysis (PCA) to draw the material space.The obtained material space shows the number of peaks in the samples prepared using DOE decreased compared to those using Dopt. In detail, the Dopt-derived sample had 41.83 peaks, while the DOE-derived sample had 19.65 peaks on average. This result indicates that we were able to efficiently find preferable compositions that are advantageous for solid solution formation by using the data-driven method.In the presentation, we will also report the high-throughput composition exploration, their conductivities, and also development of virtual X-ray diffraction simulation system for over 10,000 kinds of multi-substituted composition of the fluorides. Acknowledgement s This research was partially supported by Knowledge Hub Aichi, the GIMRT Program of the Institute for Materials Research, Tohoku University (Proposal No. 202303-CRKKE-0048).

Efficient determination of free energies of non-ideal solid solutions via hybrid Monte Carlo simulations

Predicting the phase diagram of solid solutions is crucial for understanding their physical behavior under various conditions and at different compositions. However, conventional sampling methods face challenges in efficiently addressing configurational and vibrational disorder for substitutional solid solutions. Additionally, a persistent obstacle has been the lack of a robust theoretical approach for determining the free energy of interstitial solid solutions characterized by the fluid-like diffusion of interstitial species. The method presented in this paper overcomes both hurdles by coupling thermodynamic integration with hybrid Monte Carlo algorithms. We validate the accuracy of the method by computing the free energies of iron alloys described by a Lennard-Jones potential. We also showcase its efficiency by determining the phase diagram of the MgO-CaO system, described by a machine-learning interatomic potential. The high efficiencies achieved with this method pave the way to the determination of the free energies of solid solutions with ab initio accuracy.

A highly stable insertion type V1-xTixP solid solution as an anode material for high-rate lithium-ion batteries

As electric vehicles (EVs) grow in popularity, the demand for lithium-ion batteries (LIBs) simultaneously grows, and the fast-charging capability is becoming increasingly important. However, it is generally believed that graphite anode still suffers from a poor rate capability for fast-charging applications, and other insertion-type oxide anodes with a high rate capability exhibit too high Li+-ion insertion/extraction potential, which cannot meet a requirement for high energy density anodes. In this work, the hexagonal structure of V1-xTixP (x = 0.0, 0.25, and 1.0) phases were introduced as insertion-type anode materials for LIBs with a low reaction potential of Li+-ion insertion/extraction. The crystal structure and the corresponding electrochemical reaction mechanism of insertion-type anodes of TiP, VP, and MoP were compared. A facile strategy forming a substitutional solid solution is suggested to improve the electrochemical properties of anode materials by combining the end members among insertion-type VP, TiP, and MoP as forming V1-xTixP and V1-xMoxP compounds. V1-xTixP (x = 0.25) electrode, substituting V atoms with Ti atoms in VP structure, shows excellent long-term cycle stability at 1 A/g with a cycle retention of 87.7 % during 2500 cycles, delivering a two times higher capacity of 211.1 mAh g−1 compared to that of the commercial graphite electrode.

Effect of sintering temperature on microstructure and mechanical properties of MoNbVTa0.5Cr high-entropy alloys fabricated by powder metallurgy method

To address the challenges posed by the high density and low plasticity at room temperature of traditional refractory high entropy alloys (RHEAs), the MoNbVTa0.5Cr RHEA was synthesized through a combination of mechanical alloying (MA) and spark plasma sintering (SPS) techniques. The effects of different sintering temperatures on the microstructure and mechanical properties of the alloy were systematically studied. The MoNbVTa0.5Cr RHEA milled up to 60 h was found to have a metastable dual-phase containing a major BCC (a = 3.1474 Å) and Nb-Ta (a = 3.3058 Å) phase. The sintered MoNbVTa0.5Cr RHEA was composed of BCC phase and a small amount of Ta2VO6 at different sintering temperatures. There were a lot of edge dislocations in the BCC matrix near the BCC/Ta2VO6 interface. With the increase of sintering temperature, the grain size of sintered MoNbVTa0.5Cr RHEA gradually increased, while the mechanical properties gradually decreased with the increase of sintering temperature. When the sintering temperature was 1500 °C, the grain size of the alloy was 2.33 μm, the yield strength was 2783 MPa, the compressive strength was 3346 MPa, and the fracture strain was 20.45 %, showing the best comprehensive properties. And the density of MoNbVTa0.5Cr RHEA was 9.11 g·cm−3 and 26 % lower than that of WNbMoTaV RHEA. The specific yield strength of MoNbVTa0.5Cr RHEA prepared in this research was 295.28 kPa·m3·kg−1, which was superior to most RHEAs reported so far. This sintered MoNbVTa0.5Cr RHEA showed an excellent room temperature compression performance, which can be attributed to the co-existence of BCC phase along with the minor Ta2VO6 phases. The high yield strength of MoNbVTa0.5Cr RHEA was mainly attributed to the substitutional solid solution strengthening of metal atoms, the interstitial solid solution strengthening of O atoms and the grain boundary strengthening of ultrafine grains, with contributions to yield strength of 41 %, 28 %, and 24 %, respectively.

Structure and mechanical properties of TiAlTaN thin films deposited by dcMS, HiPIMS, and hybrid dcMS/HiPIMS

The quaternary Ti1-x-yAlxTayN system exhibits superior thin film properties compared to Ti1-xAlxN. Apart from the Ta content, the sputtering method has a crucial effect on the structural and mechanical properties. High power impulse magnetron sputtering (HiPIMS) produces denser thin films with improved hardness compared to direct current magnetron sputtering (dcMS), but at lower deposition rates. However, a hybrid dcMS/HiPIMS process combines the advantages of dcMS and HiPIMS and is, therefore, a suitable method to synthetize Ti1-x-yAlxTayN thin films. To analyze the effect of the sputtering technique on the structural and mechanical properties, Ti1-x-yAlxTayN is sputtered from TiAlTa compound targets with Ta fractions up to 0.2 by dcMS, HiPIMS, and dcMS/HiPIMS.The Ta metal fraction within Ti1-x-yAlxTayN steadily increased up to y ≈ 0.25, while the Al content notably decreased at higher Ta levels. This reduction was most pronounced in HiPIMS, resulting in an order of decreasing Al content as dcMS, dcMS/HiPIMS, and HiPIMS. All thin films exhibit a Ti1-x-yAlxTayN substitutional solid solution with a linearly increasing lattice parameter corresponding to higher Ta contents. At similar Ta contents, HiPIMS-Ti1-x-yAlxTayN and dcMS/HiPIMS-Ti1-x-yAlxTayN show larger out-of-plane lattice parameters compared to dcMS/HiPIMS-Ti1-x-yAlxTayN, indicating elevated compressive stresses within the thin films. The Ti1-x-yAlxTayN thin films show a column-like structure, with HiPIMS promoting the formation of a denser morphology with less columns. The HiPIMS-Ti1-x-yAlxTayN with H = 41 GPa and dcMS/HiPIMS-Ti1-x-yAlxTayN with H = 40 GPa achieve their peak hardness at a lower Ta metal fraction of y ≈ 0.12–0.13, in contrast to dcMS-Ti1-x-yAlxTayN, which reaches H = 38 GPa at y ≈ 0.25. The shift to lower Ta contents for the maximum hardness in HiPIMS-Ti1-x-yAlxTayN and dcMS/HiPIMS-Ti1-x-yAlxTayN is due to higher compressive stresses and smaller crystallite sizes in these films at low Ta metal fractions. The H/E and H3/E2 ratios of the HiPIMS-Ti1-x-yAlxTayN and dcMS/HiPIMS-Ti1-x-yAlxTayN exhibited a similar trend of increasing values, reaching a maximum, and then decreasing with higher Ta content. Consequently, the hybrid dcMS/HiPIMS process produces Ti1-x-yAlxTayN thin films with mechanical properties comparable to pure HiPIMS, making it a suitable sputtering method for the synthesis of Ti1-x-yAlxTayN.

Сhemical synthesis of solid solutions of mercury sulfide-selenide films in the presence of sodium tartrate

Solid solutions films of mercury sulfide-selenide (HgS1–xSex) were synthesized on glass substrates by the chemical bath deposition method. Theoretical calculations of the boundary conditions for the HgS and HgSe formation in the mercury-tartrate-thiourea-selenosulfate system were made. The boundary conditions of HgS1–xSex were defined by the overlap area between the constructed HgS and HgSe formation zones. The X-ray diffraction and elemental analysis showed that the obtained films are single-phase and consist of HgS1–xSex substitutional solid solutions in zincblende modification. The effect of Na2SeSO3 concentration on the degree of S-Se substitution, as well as on the optical and morphological properties of HgS1–xSex films, was investigated.

Formation of Corrosion‐Resistant Nitride Coatings Based on Ti–Al–Cr–Fe–Ni High‐Entropy Alloy

The purpose of the work is to study the features of the phase and structure formation of coatings (Ti–Al–Cr–Fe–Ni)N formed by vacuum arc deposition and to study the influence of technological parameters of the deposition process on their corrosive properties. It is established that on the basis of the selected elements, it is possible to form a high‐entropy compound in the form of a solid solution. The structure of nitride coatings based on high‐entropy compounds formed by vacuum arc deposition is studied. It is established that the phase composition of coatings largely depends on the ratio of titanium and aluminum, which is determined by the technological parameters of deposition. An analysis of the results of the electrochemical behavior of coatings (Al,Ti,Fe,Cr,Ni)N shows that an increase in the corrosion resistance of these coatings is due to the synergistic effect of the formation of a solid substitution solution with a dense nanoscale structure and an increased relative aluminum content in them.

Bond Structure Engineering Induced the Mn Redox Stabilization Toward High‐Energy Mn‐Based Phosphate Cathode

AbstractManganese (Mn) ‐based phosphate is poised for commercial applications driven by its cost‐effectiveness, robust NASICON framework, and multi‐dimensional Na+ pathways. However, it encounters insufficient redox reactions and rapid structural collapse with severe lattice distortion as the culprit. Herein, one meticulously engineered substitutional solid solution cathode (integrating Na4MnCr(PO4)3 and Na3MnTi(PO4)3, denoted NMCTP) is proposed to regulate the local crystal structure of Mn─O bond to stabilize and promote the Mn redox reaction for optimizing the electrochemical performance. It is uncovered that the bulk framework with structural stability is constructed by strongly symmetric Mn─O bond lengths of MnO6 octahedrons and strengthened Mn─O covalency. In addition, the sufficient utilization of Mn redox is tightly correlated with redistributed Na2 occupancy and enhanced diffusion kinetics with accelerated electron transportation. By virtue of the above merits, The NMCTP performs ultra‐high capacity (150.3 mAh g−1 at 0.1 C) and appealing cycling stability (84.7% retention over 1000 cycles). Sodium storage mechanisms and potential factors at high potentials are unveiled in NMCTP materials. This work sheds light on fire‐new solid solution strengthening in view of the Mn─O bond structure for high‐performance Mn‐based phosphate cathodes.

Cyclic deformation response of annealed low-carbon steel: Insights from ratcheting and LCF experiments

Low cycle fatigue (LCF) and ratcheting experiments were carried out on annealed low-carbon steel at room temperature within a laboratory environment, utilising stress and strain control modes. The annealed low-carbon steel consistently demonstrates a cyclic softening response over its LCF lifespan, across all tested strain amplitudes. Notably, it was observed that ratcheting strain rises while ratcheting life declines with both rising mean stress and stress amplitude. Annealed low-carbon steel, being entirely ferritic and lacking precipitation or substitutional solid solution strengthening or hard phase strengthening, exhibits a restricted ability to withstand or alleviate the accumulation of ratcheting strain, particularly under very low mean stress conditions. In both LCF and ratcheting, significant substructure formation was detected. Nevertheless, there was no discernible difference in substructure formation between LCF and ratcheting when employing electron channelling contrast imaging techniques. The existing mean stress-based fatigue life prediction model has successfully forecasted ratcheting and LCF life within the 102–105 cycles range. A novel approach utilising modulus is introduced to characterise the cyclic hardening/softening behaviour of alloys in stress and strain-controlled experiments. The cyclic hardening model based on modulus effectively captures the responses observed in cyclic hardening/softening during LCF and ratcheting experiments.

Electron Transport Properties of Eu(Cu1 − xAgx)2Si2 (0 ≤ x ≤ 1): Initiation of Transition Eu2+ ↔ Eu2.41+ in the Intermediate Valence State

The article presents the results of studies of the chemical composition, crystal structure, lattice parameters, microstructure, the valence state of the europium ion (at 300 K), electrical resistivity, and differential thermopower (6–400 K) of samples in the Eu(Cu1 − xAgx)2Si2 (0 ≤ x ≤ 1) substitutional solid solutions. A transition of the europium ion from the valence-stable state of Eu2+ in EuAg2Si2 to the state of intermediate (homogeneous) valence (IV) of the europium ion in EuCu2Si2 with an effective valence ϑeff = 2.41 (300 K) has been initiated by a successive replacement of silver atoms by copper atoms. With appropriate sample compositions, the transition passes through a Kondo-type state. The research subject is the patterns of transformations (when the composition of the sample changes), the electronic state, and, accordingly, the electronic transport properties. The simultaneous coexistence of europium ions in different electronic states is assumed. The substitutional solid solution Eu(Cu1 − xAgx)2Si2 (0 ≤ x ≤ 1) exhibits properties related to the competition between the state of the Kondo system, intermediate valence (IV), and magnetic ordering.

Quantitative analysis of element substitution in mixed-vanadate LuxGd1-xVO4 single crystals at the atomic scale

In mixed crystals, two or more elements exhibit comparable properties and can be substituted freely. As a special type of “substitutional doping,” the properties of materials can be adjusted by altering the doping ratio of elements. Mixed-vanadate crystal LuxGd1-xVO4 is a promising laser host material with excellent chemical stability, mechanical property and thermal conductivity. The substitutional doping ratio of the two rare-earth elements determines the value of x. The thermal, optical, and laser properties of the material vary with x. However, the two types of atoms showing little difference in the same location in mixed crystals form substitutional solid solutions with alike atomic radii as well as electronic structures. Therefore, distinguishing comparable elements in mixed crystals at the atomic scale and quantitatively analyzing the doping ratio in mixed crystals are challenging. In this study, combining high-angle annular dark field (HAADF) and electron energy-loss spectroscopy (EELS), we accurately characterize the atomic structure of mixed-vanadate single crystal LuxGd1-xVO4 along the [111] orientation as well as the distribution of two rare-earth elements at the atomic scale. The ratio of Lu and Gd and the doping rules in the crystals are quantitatively analyzed. In addition, combined with the energy dispersive X-ray spectroscopy (EDS) results of the [100] crystal orientation, a uniform random distribution of Lu and Gd in the LuxGd1-xVO4 crystal is confirmed. This study provides a new means of understanding mixed-crystal structures and solves the problem of quantitative analysis of elemental doping in materials at the atomic scale, thus laying the foundation for exploring the relationships among composition, structure, and function in materials.

Cerium Dioxide as an Electron Buffer to Stabilize Iridium for Efficient Water Electrolysis

AbstractSustaining the steady state for highly active non‐stoichiometric iridium (Ir)‐based oxide (IrOx) at low Ir loading remains challenging primarily due to the continuous oxidation and sequent dissolution of Ir active sites during the oxygen evolution reaction (OER). In this context, a new iridium–cerium (Ce) substitution solid solution oxide (SSO) has been developed, featuring uniformly dispersed Ir atoms within Ce dioxide (CeO2) matrix as electron buffer, which delivers remarkable acidic OER catalytic activity and enhanced stability. The electron‐buffering capacity of CeO2 facilitates the charge transfer toward Ir atoms, leading to abundant active low‐valence Ir sites and effectively prevent their oxidation and dissolution. As a result, Ir─Ce SSO demonstrates an overpotential of merely 238 mV@10 mA cm−2. Proton exchange membrane water electrolyzer employing Ir─Ce SSO at a low Ir loading of 396 µgIr cm−2 operates consistently for over 100 h@500 mA cm−2. Density functional theory (DFT) calculations corroborate that the electron‐buffering effect of CeO2 enriches the density of IrIII and substantially increases the dissolution energy barrier of Ir atoms. This study presents a viable approach to addressing the issues of instability and low efficiency in Ir‐based OER electrocatalysts for acidic water electrolysis.

Substitutional and interstitial atoms co-doping overcomes the strength–ductility trade-off in lightweight refractory medium-entropy alloys

Interstitial or substitutional solid solution strengthening is a common method for enhancing material mechanical properties, however, it is unclear whether their synergy can lead to better mechanical properties in materials. Here, we have demonstrated that the synergy of interstitial and substitutional elements can overcome the strength-ductility trade-off, which was substantiated in an O and Al co-doping (TiZrNb)94.5O0.5Al5 (O0.5Al5) lightweight refractory medium-entropy alloy (LRMEA) with a density ∼6.0 g/cm3. The co-doping LRMEA exhibits a simultaneous enhancement in strength and ductility with a yield strength of ∼1025 MPa and a fracture elongation of ∼35%, compared with the O or Al single doped alloys, i.e. (TiZrNb)99.5O0.5 (O0.5) and (TiZrNb)95Al5 (Al5). This combined increase in strength and ductility was attributed to synergistic interstitial and substitutional solid solution strengthening and the modification of dislocation motion mode from planar slip delocalization to a relatively diffuse, three-dimensional dislocation pattern, effectively alleviating stress concentration. This work provides valuable insight into the development of high-performance lightweight alloys.