Atomic Size Research Articles

Mechanical, Thermal Properties, and Extreme Phase Stability of High-Entropy Diborides (V0.2Nb0.2Ta0.2Cr0.2W0.2)B2.

High-entropy diborides (HEDBs) have gained significant attention in industrial applications due to their vast composition space and tunable properties. We propose a solid solution reaction at high temperatures and pressures that successfully synthesized and sintered a novel, dense, and phase-pure HEDB (V0.2Nb0.2Ta0.2Cr0.2W0.2)B2. A high asymptotic Vickers hardness of 26.3 ± 0.6 GPa and a bulk modulus of 320.5 ± 10.6 GPa were obtained. Additionally, we investigated the thermal oxidation process using TG-DSC from room temperature to 1500 °C and explored the phase stability of HEDBs under high-pressure conditions through in situ high-pressure synchrotron radiation X-ray diffraction. We analyzed the formation of lattice distortion, chemical bonding, and band structure in (V0.2Nb0.2Ta0.2Cr0.2W0.2)B2 using first-principles calculations. Surprisingly, we found that the predominant distortion in diborides occurs in the boron layer, supported by ELF. This may be due to uneven electron transfer rather than a straightforward correlation with the atomic radius. These results provide a novel synthesis process and additional experimental data on the mechanical and thermal properties and high-pressure phase stability of HEDBs. Our study offers further insights into the microscopic structure of lattice distortion in HEDBs, which could prove crucial for the selection and design of engineering advanced HEDBs.

Atomic size mismatch induced consecutive compressive strain on intermetallic compound towards boosted hydrogen evolution

AbstractModulating lattice strain in intermetallic compounds could effectively alter their electronic structure and binding energy, thus impacting catalytic activity. Strain is usually induced through lattice mismatch, achieved by constructing core‐shell nanostructures or metal‐substrate interfaces with complex reciprocity and distractors. However, in situ induced strain without interface‐construction or lattice mismatch presents challenges. In this study, we precisely manipulate consecutive compressive strain from −0.5% to −0.8% in CoPt3Pd intermetallic compound by inducing interior atomic radius mismatch. Precise strain control results in a negative shift of d‐band center, dynamic charge distribution, and facilitates water dissociation, leading to enhanced electrocatalytic activity. The CoPt3Pd catalyst with −0.5% compressive strain exhibits exceptional hydrogen evolution activity, with an overpotential of 169 mV at 1 A cm−2. Our approach offers a straightforward method to manipulate compressive strain on intermetallic compounds by atomic size mismatch, with broad implications for catalytic processes.

Enhancing elastocaloric performance: Ti-doped Co–V-Ga bulk polycrystalline alloys with minimal stress hysteresis

Currently, practical applications of shape memory alloy (SMA) solid elastocaloric refrigeration materials are limited by low elastocaloric effect (eCE), high applied stress, and large stress hysteresis (Δσhys). Here, we introduce a composition design strategy using Ti-doped Co–V-Ga SMAs to address these challenges. We combine first-principles calculations and experiments to verify this strategy. Our results show that the lattice distortion caused by the significant difference in atomic radius after Ti doping produces a solid solution strengthening effect inside the alloy, which significantly improves the superelasticity of the alloy, delays the plastic deformation of the austenite phase, and the volume fraction of martensitic transformation increases significantly. The newly developed Co51.7V31.3Ga16Ti1 bulk polycrystalline alloy exhibits a remarkable adiabatic temperature change (ΔTad) of −10 K at room temperature under a low stress of 400 MPa, a minimum Δσhys of 18 MPa, and a high coefficient of performance COPmat of 31.9. Importantly, the 100-cycle loading-unloading test at 350 MPa is done, and it reveals that the ΔTad for the Ti0 alloy was only 3.9 K, while it reached 6.2 K for the Ti1 alloy, marking a noteworthy 59 % performance enhancement. From the simplicity of the fabrication process to the comprehensive performance of the material, it exhibits a promising advantage for practical cooling applications This study presents a feasible design strategy for large-scale production of high-performance bulk polycrystalline alloys with high eCE, low stress, and Δσhys.

Exploring the roles of atomic radius on methane oxidation in different M(Y, Sm, and Ni)-doped CeO2 catalysts using operando DRIFTS-MS and DFT computation

Ce-based oxides doped with different metal ions can greatly improve CH4 catalytic activity, but the relationship between the surface microstructure and its activity is not clear. In this article, M(Y, Sm, and Ni)-CeO2 catalyst prepared by aerosol method is used as the research object. CH4 is used as a molecular probe for the study. Operando DRIFTS-MS and DFT computation are used to verify the structure-activity relationship between the surface structure and activity of M-CeO2. Ni-CeO2 with the smallest atomic radius ratio has the best CH4 oxidation performance (550 °C) and excellent redox characteristics. Operando DRIFTS-MS results show that the NiO is more likely to adsorb CH4 and form the intermediates CH3*, gas-phase CO2, CO, and H2O at low temperatures. At high temperatures, Ni-OH, Ni-O-Ce, and CeO further react with CH4. Among them, the formation of M-Ov-Ce has a positive role in promoting the decomposition of O₂. Importantly, carbonate is the rate-determining step that affects the activation of M-Ov-Ce. Monodentate carbonates decompose more easily at low temperatures. These findings reveal a novel doping effect and provide a new idea for the design and development of Ce based catalysts with high CH4 removal ability

In-situ deformation mechanisms of a novel Ti-5Mo-4Cr-1V-1Zr metastable β titanium alloy

To overcome the strength-plasticity trade-off in the structural titanium alloys, a novel metastable β titanium alloy Ti-5Mo-4Cr-1V-1Zr (Ti-5411) with high strength and high plasticity was designed by the d-electrons theory, average electron-to-atom ratio (e/α‾) and atomic radius difference (Δr‾) theory. Combined in-situ scanning electron microscope (SEM) and electron backscatter diffraction (EBSD), the deformation mechanisms of the novel Ti-5411 metastable β titanium alloy were systematically investigated. The results show that the Ti-5411 alloy exhibits excellent yield strength (∼689 MPa), tensile strength (∼930 MPa) and total elongation (∼39%). The in-situ tension indicates that slip activities, crystal rotation, stress induced martensite (SIM) α″ transformation and {332}<113> deformation twin are the major deformation mechanisms of Ti-5411 alloy. Besides, with the increase of strain degree (0–0.5 mm displacement), deformation twins increase, widen and interlace. At 0.35 mm tensile displacement, the orientation of the β grains rotates ∼6.65° to accommodate the increased macrostrain. Additionally, martensite α″ also assists the nucleation of twins. Some {332}<113> twins grow and merge by consuming martensite α″ during deformation, and the residual martensite α″ remains in the merged twins.

Composition-Structure-Property links in rocksalt AgMnGeSbTe high-entropy alloys: Insights from experiments and deep learning potential atomic simulations

High-entropy alloys (HEAs), particularly AgMnGeSbTex, are emerging as notable thermoelectric materials with excellent structural stability and tailored electronic properties. This study investigates these alloys through both experimental and computational methods. Thin films of AgMnGeSbTex with varying Te content (x = 1–4) were produced using magnetron co-sputtering on glass substrates. Structural analysis showed a transition from α-Ag2Te to a high-entropy rocksalt structure with increased Te content, with x = 4 yielding the optimal structure. Enhanced electrical properties, such as conductivity and Seebeck coefficient, were observed in the rocksalt films x = 3 and x = 4. Atomistic simulations using a deep learning potential (DLP) highlighted the importance of atomic size differences in mechanical behavior, with specific compositions showing increased ductility. Heating simulations revealed phase changes and amorphization at melting points. This research advances the understanding of the composition-structure–property relationships in high-entropy rocksalt alloys, with the x = 4 film showing promising thermoelectric potential. This study demonstrates the effectiveness of combining experimental and simulation approaches in exploring complex high-entropy systems for knowledge-driven materials design.

Machine learning-enabled prediction and optimization of hardness for Nb-Ti-V-Zr refractory high entropy alloy

High entropy alloy (HEA) design strategies have been limited to experimental trial-and-error approaches. However, due to the vast compositional space of HEAs, efficiently discovering new HEAs with exceptional performance using trial-and-error methodology is time-consuming and challenging. In this work, a machine learning (ML) framework was introduced for Nb-Ti-V-Zr refractory HEA (RHEA) design. This framework aims to streamline the design of Nb-Ti-V-Zr RHEA with a focus on improving hardness. This framework encompasses data collection, feature construction, four-step feature selection, and training of different ML models, followed by Fisher material pattern recognition and SHAP feature analysis. For the first time, three key features, including the atomic size difference (δ), the configurational entropy of mixture (Smix), and the average deviation of electronegativity (AdE) were identified as the most significant compositional factors impacting the hardness of Nb-Ti-V-Zr RHEA. Furthermore, the Support Vector Regression (SVR) model with a polynomial kernel was the best-trained model for hardness prediction compared to other ML models trained and tested in this work. The coefficient of determination (R) was 0.85 for the testing set and 0.91 for 5-fold cross-validation, while the root mean square error (RMSE) values were 0.9 and 0.74, respectively. Moreover, it was observed that high-hardness samples follow a particular combination of key features, providing important optimization insights. Finally, the analysis of key features revealed the negative effect of AdE, the positive effect of Smix, and the hybrid effect of δ on hardness.

Highly efficient adsorption of aqueous heavy metals by Co-derived metal-organic framework. Synergistic mechanism for enhanced water purification

This study opens up exciting possibilities for the application of Co-MOF, a Metal-Organic Framework ([Co(5-NH2-bdc)(bpy)0.5(H2O)]3·2H2O), in the efficient removal of heavy metals (Pb2+, Hg2+, Cd2+, Cu2+) from water. The removal mechanism combines ion exchange and adsorption, influenced by the ionic radius of the metal ions. Langmuir's model determined maximum adsorption capacities (Qm), showing a proportional increase with the ionic radius of heavy metals: 75.47 mg/g (Cu2+), 344.82 mg/g (Cd2+), 485 mg/g (Hg2+), and 526.31 mg/g (Pb2+). Free Gibbs energy, inversely proportional to the metal's ionic radius, was determined as −36.43 kKj/mol (Cu2+), −28.67 Kj/mol (Cd2+), −24.13 Kj/mol (Pb2+), and −21.67 Kj/mol (Hg2+). The pseudo-second-order mechanism explained heavy metal removal, except for Cu2+, due to continuous ion exchange. Reutilization experiments showed a decrement in efficacy in the second cycle. Filtration experiments demonstrated a lower removal percentage (close to 60 %) and confirmed the competitive activity of Co-MOF compared to other MOFs, particularly in Cd2+ removal, with superior rate constants and maximum adsorption capacities.

Insights into the optoelectronic, thermodynamic, and thermoelectric properties of novel BaYCuX3 (X = Se, Te) semiconductors from first-principles investigation

The widely used density functional theory was employed to study an intricate relationship of the optoelectronic, thermodynamic, and transport features of novel quaternary BaYCuX3 (X = Se, Te) semiconductors. The conduction band region is significantly impacted by the Ba-d and Y-d states, with negligible contributions from the S-s/p/d and Te-s/p/d states. The valence and conduction bands peak at the high symmetry Γ and Y sites, revealing an indirect energy band nature. The predicted band gaps for the BaYCuSe3 and BaYCuTe3 using the WC-GGA and TB-mBJ approximations are 0.96, 1.31 eV, and 0.54, 0.89 eV, respectively. The small atomic size of selenium in BaYCuSe3 material contributes to strong bonding, resulting in a larger energy gap as compared to BaYCuTe3. Maximum values of ε1(ω) drop as photon frequency increases, eventually approaching negative in some energy ranges. The absorption coefficient spectra shifted toward lower energy as the anion changed from Se to Te. Furthermore, the BaYCuTe3 has plasmon resonances at higher energies as compared to BaYCuSe3, resulting in increased energy loss. Furthermore, the BaYCuTe3 material exhibits maximum thermal conductivity than BaYCuSe3 across the whole temperature range.

Evolution of microstructure, mechanical properties and phase stability of CoCrFeMnNi high entropy alloys

In the present study, the microstructure and mechanical properties of various CoCrFeMnNi high-entropy alloys were investigated. Analytical studies were conducted to determine the optimal chemical composition, mixing entropy, mixing enthalpy, atomic radii, valence electron concentration (VEC), dimensionless parameter, and melting point on the Co-Cr-Fe-Mn-Ni system. The microstructure of the alloys was analyzed using FESEM, XRD, and TEM. The results showed that the microstructure of all HEAs had dendritic and interdendritic regions, with secondary precipitations detected along the grain boundaries of the alloy, mainly composed of Mn and Ni. High-density dislocation structures and nano-precipitates were predominantly present in the alloy. The mechanical characteristics such as microhardness and tensile properties are conducted at room temperature. The HEA Co25Cr25Fe10Mn30Ni10 exhibited the highest average microhardness, while the Co20Cr20Fe30Mn10Ni20 HEA had the lowest mean hardness value. This significant difference of 7.2 % may be attributed to the hard phases composed of Mn and Ni. The results of the tensile experiments indicate that the Co20Cr20Fe20Mn20Ni20 alloy has the most favorable overall properties, with an ultimate tensile strength of 441 MPa. This represents a significant increase of 37.8 % compared to 20Cr20Fe20Mn20Ni20. Furthermore, the study examines the instability of the solid-solution state caused by differences in the valence electron concentrations of the constituent elements and phase stability.

Determination of stability constants of Cu(II)2-bistren cascade complexes by cellmetry method

Cu(II)2-bistren cascade complexes were studied by cellmetry methodology where by choosing appropriate cell sizes of the box the logK values can be calculated by a plane wave DFT method. Different types of anions were chosen to study the effect of the size, shape, and bite length of the donor atoms on the stability constants. It was found that the ligand strain needs to be taken into account to calculate reasonable logK values. Correction factors were determined regarding the energy of the anions and the length of the bistren ligands which resulted in accurate calculated stability constants for all types of anions.

Revealing the effects of asymmetric M-O-Ce structure on CO oxidation over M(Cu, Mn, Fe, La and Zr)-doped CeO2 catalysts: Atomic radius and oxygen vacancies

Although CeO2 catalysts doped with different metal ions can significantly enhance CO activity, the intrinsic relationship between these activities and the catalyst structure is still not clearly understood. In this paper, M(Cu, Mn, Fe, La and Zr)-doped CeO2 catalysts prepared by aerosol method are used as research targets for CO oxidation. Cu-CeO2 with the smallest atomic radius ratio has the best redox capacity and more oxygen vacancy content. DFT results show that promoting the interface effect in the presence of Cu-Ov-Ce is conducive to enhancing CO adsorption capacity. Operando TPR-DRIFTS-MS results reveal that different types of oxygen species (including M=O, CeO, M-O-Ce, and M-OH) exhibit different reactivity on the surface of Ce-based catalysts. M(Cu, Mn, Fe, La and Zr)=O is more likely to react with CO above 100°C. CeO, M-O-Ce, and M-OH also react with CO to form oxygen vacancies (such as M-Ov-Ce and CeOv) and CO2 after reaching a certain temperature. Among them, the formation of M-Ov-Ce has a positive role in promoting the decomposition of O₂. Importantly, carbonate is the rate-determining step that affects the activation of M-Ov-Ce. Monodentate carbonates decompose more easily at low temperatures. These findings reveal a novel doping effect and provide a new idea for the design and development of Ce based catalysts with high CO removal ability.

A strategy for high-entropy copper alloys composition design assisted by deep learning based on data reconstruction and network structure optimization

Complex mapping relationships between high-entropy alloy compositions and performances struggle to precisely elucidate by traditional machine learning models, hindering the accurate and efficient design of high-performance alloys. In this work, a novel alloy design strategy combined self-decision deep neural network, data reconstruction with network structure optimization was proposed, which effectively enhanced the model's ability to predict the mapping relationships between high-dimensional composition spaces and mechanical properties of alloy. Compared to other machine learning methods, significantly improves model prediction accuracy (hardness model: 97.98%; strength model: 94.40%). Through above model, the mechanical properties of 308 new (CuNiMn)-X high-entropy copper alloys was studied added other elements such as Al, Ti, Cr, and Fe, which designed and produced a novel (CuNiMn)60Al20Cr20 alloy with high hardness of 474 HV, high compressive strength of 2322 MPa, and high fracture strain of 25.20%. The primary factors influencing alloy performance and their respective thresholds were also quantitatively revealed (hardness: electronegativity deviation (0.02, 0.1) and nuclear charge deviation (0, 0.25); compressive strength: mean nuclear charge (25, 30) and mean atomic radius (134 p.m.)). These findings provide a new perspective and approach for the design and mechanism understanding of high-performance alloys with complex compositions.

High-throughput screening of single-atom catalysts on 1 T-TMD for highly active and selective CO2 reduction reaction: Computational and machine learning insights

The study of transition metals and various possible surface compositions has sparked great interest in low-cost materials, which exhibit high activity and selectivity in catalysis. While various single-atom catalysts loaded on transition metal dichalcogenide (TMD) substrates with excellent CO2 reduction performance have been identified, the relationship between catalytic activity and the intrinsic properties of TMD single-atom catalysts remains unclear. Hence, a high-throughput first-principle computational approach is proposed to screen 24 transition metals anchored on 8 TMD monolayers to determine their catalytic activity in CO2RR. The results show that Fe@CoS2, Pt@TiTe2 and Co@CoS2 exhibit exceptional performances with low CO2RR limiting-potentials of −0.045 eV, 0.75 eV, and 0.54 eV, respectively, showcasing selective pathways towards formic acid (HCOOH), methane (CH4), and methanol (CH3OH). Employing the Sure Independence Screening and Sparsifying Operator method(SISSO), key descriptors linking the performance of single-atom catalysts with their intrinsic features are identified, providing insights for the discovery of superior CO2RR catalysts. Moreover, it was observed that a feature of the anchored single atom, the difference between covalent radius and atomic radius (CR-R), is associated with multiple crucial reaction steps, exhibiting a strong linear relationship with the charge transfer of *COOH. This work not only identifies promising CO2RR catalysts but also establishes a predictive framework for screening catalysts based on their intrinsic properties, paving the way for future advancements in CO2 reduction research.

Noncentrosymmetric, transverse structural modulation in SrAl4 , and elucidation of its origin in the BaAl4 family of compounds

At ambient conditions SrAl4 adopts the BaAl4 structure type with space group I4/mmm. It undergoes a charge-density-wave (CDW) transition at TCDW=243 K, followed by a structural transition at TS=87 K. Temperature-dependent single-crystal x-ray diffraction (SXRD) leads to the observation of incommensurate superlattice reflections at q=σc* with σ=0.1116 at 200 K. The CDW has orthorhombic symmetry with the noncentrosymmetric superspace group F222(00σ)00s, where F222 is a subgroup of Fmmm as well as of I4/mmm. Atomic displacements mainly represent a transverse wave, with displacements that are 90 deg out of phase between the two diagonal directions of the I-centered unit cell, resulting in a helical wave. Small longitudinal displacements are provided by the second harmonic modulation. The orthorhombic phase realized in SrAl4 is similar to that found in EuAl4, except that no second harmonic could be determined for the latter compound. Electronic structure calculations and phonon calculations by density functional theory (DFT) have failed to reveal the mechanism of CDW formation. No clear Fermi surface nesting, electron-phonon coupling, or involvement of Dirac points could be established. However, DFT reveals that Al atoms dominate the density of states near the Fermi level, thus corroborating the SXRD measurements. SrAl4 remains incommensurately modulated at the structural transition, where the symmetry lowers from orthorhombic to b-unique monoclinic. The present work draws a comparison on the modulated structures of nonmagnetic SrAl4 and magnetic EuAl4 elucidating their similarities and differences, and firmly establishing that although substitution of Eu to Sr plays little to no role in the structure, the transition temperatures are affected by the atomic sizes. We have identified a simple criterion that correlates the presence of a phase transition with the interatomic distances. Only those compounds XAl4−xGax (X=Ba, Eu, Sr, Ca; 0&lt;x&lt;4) undergo phase transitions, for which the ratio c/a falls within the narrow range 2.51&lt;c/a&lt;2.54. Published by the American Physical Society 2024

Effect of laser energy density on microstructure and critical current of YGBCO and HGBCO films fabricated by PLD

Y0.5Gd0.5Ba2Cu3O7-σ (YGBCO) and Ho0.5Gd0.5Ba2Cu3O7-σ (HGBCO) targets with similar densities were prepared by solid-phase reaction. Pulsed laser deposition (PLD) technology was used to fabricate superconducting films with these targets. During the experiments in this paper, we varied the laser energy by adjusting the optical lens. The structure and texture of RE0.5Gd0.5Ba2Cu3O7-σ (REGBCO, where RE = Y, Ho) thin films were analyzed by X-ray diffraction (XRD). The surface morphology was observed by atomic force microscopy (AFM) and scanning electron microscopy (SEM), and the superconducting critical current was measured at 77 K using the standard four-probe method. The laser energy density and different doping elements can affect the properties of REGBCO films. This may be related to the ejection process of target particles and the size of rare earth atoms. Additionally, we prepared a 510-meter long second-generation high-temperature superconducting tape with the optimized parameters. The critical current of the tape is 350 A, and the current density is 3.9 × 106 A/cm2.

Enhancing the Strength and Ductility Synergy of Lightweight Ti-Rich Medium-Entropy Alloys through Ni Microalloying.

Medium-entropy alloys (MEAs) have attracted considerable attention in recent decades due to their exceptional material properties and design flexibility. In this study, lightweight and non-equiatomic MEAs with low density (~5 g/cm3), high strength (yield strength: 1200 MPa), and high ductility (plastic deformation: ≧10%) were explored. We fine-tuned a previously developed Ti-rich MEA by microalloying it with small amounts of Ni (reducing the atomic radius and increasing the elastic modulus) through solid solution strengthening to achieve a series of MEAs with enhanced mechanical properties. Among the prepared MEAs, Ti65Ni1 and Ti65Ni3 exhibited optimal properties in terms of the balance between strength and ductility. Furthermore, the Ti65Ni3 MEA was subjected to thermo-mechanical treatment (TMT) followed by cold rolling 70% (CR70) and cold rolling 85% (CR85). Subsequently, the processed samples were rapidly annealed at 743 °C, 770 °C, 817 °C, and 889 °C at a heating rate of 15 °C/s. X-ray diffraction analysis revealed that the MEA could retain its single-body-centered cubic solid solution structure after TMT. Additionally, the tensile testing results revealed that increasing the annealing temperature led to a decrease in yield strength and an increase in ductility. Notably, the Ti65Ni3 MEA sample that was subjected to CR70 and CR85 processing and annealed for 30 s exhibited high yield strength (>1250 MPa) and ductility (>13%). In particular, the Ti65Ni3 MEA subjected to CR85 exhibited a specific yield strength of 264 MPa·cm3/g, specific tensile strength of 300 MPa·cm3/g, and ductility of >13%.

Navigating the 18-n+m Isomers of PdSn2: Chemical Pressure Relief through Isolobal Bonds and Main Group Clustering.

The 18-n electron-counting rule provides structural guidelines for electronically feasible transition metal (T)-main group (E) phases, contributing toward the goal of material design. However, the availability of numerous potential structure types at any electron count creates a challenge for the prediction of the preferred structures of specific compounds, as is illustrated by the concept of 18-n+m isomerism. In this Article, we explore the driving forces stabilizing one 18-n+m isomer over another with an analysis of the structure of PdSn2, a layered intergrowth of the fluorite and CuAl2 structure types. The DFT-reversed approximation Molecular Orbital (DFT-raMO) method reveals that PdSn2 and its hypothetical parent structures all adhere to bonding schemes approximating the electronic configurations expected from the 18-n rule, with various degrees of isolobal Pd-Pd bonding and Sn clustering. However, partial electron transfer between the Pd 5p orbitals to the Sn 5s orbitals contributes to the absence of convincing electronic pseudogaps near their Fermi energies. As such, there is no clear electronically driven preference among the structure types. This situation allows for atomic packing effects to prevail: DFT-Chemical Pressure (DFT-CP) analysis illustrates that in the fluorite-type parent structure, positive Pd-Sn CPs lead to overcompression of the Pd atoms and a stretching of the relatively open Sn sublattice. In contrast, in the CuAl2-type parent structure, Sn atoms cluster into tetrahedra, opening space for an expanded Pd environment and the formation of Pd-Pd interactions. However, the tetrahedral packing of the Sn atoms here leads to frustration between negative and positive Sn-Sn CPs. Through the development of the angular CP correlation function (CPcor+) as a tool to quantify frustration among interatomic interactions, we demonstrate how the observed PdSn2 structure balances these effects by tuning the degree of Sn-Sn clustering and expansion of the Pd environment. These observations point to generalizations for most 18-n+m isomers, where increased main group ligand clustering (+m) and isolobal bonds (+n) can accommodate compositions with different T and E atomic sizes.

Fabrication, microstructure, and properties of Dy‐doped (Y1−xDyx)3Si2C2 ceramics fabricated by in situ reactive spark plasma sintering

AbstractDysprosium (Dy)‐doped (Y1−xDyx)3Si2C2 (x = 0, 0.1, 0.3, 0.5) solid solution ceramics were successfully fabricated using an in situ reaction spark plasma sintering technology, for the first time. The effect of various Dy doping contents (x) on the microstructure, mechanical, and thermal properties of (Y1−xDyx)3Si2C2 ceramics was investigated. The (0 2 0) crystal plane spacing of (Y0.5Dy0.5)3Si2C2 was 7.813 Å, which was smaller than that of Y3Si2C2, due to the fact that the atomic radius of Dy is smaller than that of Y. The Dy doping facilitated the consolidation of (Y1−xDyx)3Si2C2, thus a highly dense (Y0.5Dy0.5)3Si2C2 ceramic material with a low open porosity of 0.14% was successfully obtained at a relatively low temperature of 1 200°C. As the content of Dy doping (x) increased from 0 to 0.5, the purity of (Y1−xDyx)3Si2C2 ceramics increased from 88.3 to 90.7 wt.%, while the grain size of (Y1−xDyx)3Si2C2 ceramics decreased from 0.59 to 0.46 µm. As a result, the Vickers hardness and thermal conductivity of the (Y0.5Dy0.5)3Si2C2 material was 7.1 GPa and 9.8 W·m−1·K−1, respectively.

Mechanistic understanding of speciated oxide growth in high entropy alloys

Complex multi-element alloys are gaining prominence for structural applications, supplementing steels, and superalloys. Understanding the impact of each element on alloy surfaces due to oxidation is vital in maintaining material integrity. This study investigates oxidation mechanisms in these alloys using a model five-element equiatomic CoCrFeNiMn alloy, in a controlled oxygen environment. The oxidation-induced surface changes correlate with each element’s interactive tendencies with the environment, guided by thermodynamics. Initial oxidation stages follow atomic size and redox potential, with the latter becoming dominant over time, causing composition inversion. The study employs in-situ atom probe tomography, transmission electron microscopy, and X-ray absorption near-edge structure techniques to elucidate the oxidation process and surface oxide structure evolution. Our findings deconvolute the mechanism for compositional and structural changes in the oxide film and will pave the way for a predictive design of complex alloys with improved resistance to oxidation under extreme conditions.