Difference In Atomic Radii Research Articles

Predicting single-phase solid solutions in as-sputtered high entropy alloys: High-throughput screening with machine-learning model

Searching for single-phase solid solutions (SPSSs) in high-entropy alloys (HEAs) is a prerequisite for the intentional design and manipulation of microstructures of alloys in vast composition space. However, to date, reported SPSS HEAs are still rare due to the lack of reliable guiding principles for the synthesis of new SPSS HEAs. Here, we demonstrate an ensemble machine-learning method capable of discovering SPSS HEAs by directly predicting quinary phase diagrams based only on atomic composition. A total of 2198 experimental structure data are extracted from as-sputtered quinary HEAs in the literature and used to train a random forest classifier (termed AS-RF) utilizing bagging, achieving a prediction accuracy of 94.6% compared with experimental results. The AS-RF model is then utilized to predict 224 quinary phase diagrams including ∼32,000 SPSS HEAs in Cr-Co-Fe-Ni-Mn-Cu-Al composition space. The extrapolation capability of the AS-RF model is then validated by performing first-principle calculations using density functional theory as a benchmark for the predicted phase transition of newly predicted HEAs. Finally, interpretation of the AS-RF model weighting of the input parameters also sheds light on the driving forces behind HEA formation in sputtered systems with the main contributors being: valance electron concentration, work function, atomic radius difference and elementary symmetries.

Relationship between hydrogen permeability and the physical-chemical characteristics of metal alloy membranes

Due to the vast compositional range of advanced hydrogen-selective alloys, quantitative and well-targeted development are extremely challenging. This paper examines a wide range of bond properties related to high-H2 permeability metal membranes. An investigation of the relationships between hydrogen (H2) permeability and physical-chemical characteristics, namely, atomic radius difference (δ), mixed entropy (ΔS), electronegativity difference (Δχ), and valence electron concentration (VEC), was proposed using a data set of 170H2 permeation experiments at 673 K collected from about 70 scientific literature references regarding Pd-, Ni-, Nb-, Ti-, V-, and Zr-based binary, ternary, or more complex alloy membranes. The following conclusions can be drawn from the selected experimental data collected in the literature: It seems that for the metal alloy membranes, the H2 permeation properties have a close correlation to bond parameters. On the whole, the H2 permeability increased as the VEC decreased, regardless of alloy membranes and other characteristics. If light VEC metals are considered to consist of any metal having a relatively low valence electron concentration, light VEC alloys are seen to be the greatest options for achieving high H2 permeability. Our physical-chemical criterion, which is based on the bond properties of metal alloy membranes, can be utilized to both create new H2-selective alloy membranes and improve the efficiency of currently studied membranes.

Theoretical prediction of two-dimensional II-V compounds

Graphene has attracted significant attention as a pioneer of two-dimensional zero gap semiconductors, but the development of new two-dimensional materials with a finite band gap has been actively pursued. In this study, the structural stability of double bilayers (DBs) of group II-V compounds (II: Be, Zn, and Cd; V: P, As, and Sb) has been systematically investigated using first-principles calculations based on density functional theory. The thermodynamic calculations have confirmed that BeP, BeAs, ZnP, and ZnAs can be produced through exothermic reactions from their constituent bulk systems. It has also been confirmed that all the compounds have phonon dynamical stabilities. Only CdP and CdAs have been found to have an AB-stacked DB structure with threefold symmetry, while the other compounds have ${\text{AB}}^{\ensuremath{'}}$-stacked DB structure with broken symmetry. The difference in atomic radii between group II and group V results in the so-called size effect, which determines the stacking pattern. The structural stability of II-V DB thin films is explained by analogy with the surface structural stability of compound semiconductors: The change in the atomic arrangement of the DB structure alters the electronegativity of the surface orbitals of the II-V thin film, which does not result in any unsaturated bonds, i.e., no metallic bands across the Fermi level appear. The various DB II-V compounds proposed in this study will join the ranks of atomic-level 2D semiconductor materials.

ZnO/Ag multilayer for enhancing the catalytic activity against 4-nitrophenol

A multilayer thin film from zinc oxide and silver (ZnO/Ag multilayer thin film) has been synthesized via the technique of pulsed infrared laser deposition at 600 °C to be used as a portable catalyst for the degradation of 4-nitrophenol. The multilayer thin film was formed by two steps; the first one was making a thin film with a 300 nm thickness, followed by a 100 nm thin film from Ag, which was characterized by different characterization techniques. The XRD data demonstrated the presence of hexagonal Ag on ZnO in the formation of ZnO thin films and ZnO/Ag thin films. Also, it showed that crystallite size is decreasing as the Ag concentration rises because of the difference in atomic radius between Zn and Ag atoms in the crystal structure formation of ZnO coated with Ag. The crystal quality of ZnO and Ag was evaluated using photoluminescence (PL). The optical investigation showed the decrease in transmittance after coating ZnO film with Ag was due to ZnO films including more voids than ZnO/Ag films. From SEM images, the morphology of ZnO films was modified by the appearance of brilliant spots, which was related to the coating of the Ag layer as confirmed by elemental analysis. Then, based on the findings of catalytic experiments against 4-nitrophenol, the ZnO/Ag multilayer thin film shows an exceptional potential enhancement in compared to that of ZnO thin film.

Mechanism of nitrogen-doped biocharactivated peroxymonosulfate for degradation of 2,4-dichlorophenol.

Biocharactivated peroxymonosulfate has been widely used to degrade organic pollutants. However, the chemical inertness of the sp2 hybrid conjugated carbon framework and the limited number of active sites on the pristine biochar resulted in the low catalytic activity of the system, restricting its further application. In this study, nitrogen-doped biochar was prepared following a simple one-step synthesis method taking advantage of the similar atomic radius and significant difference in electronegativity of N and C atoms to explore the properties and mechanisms of biochar-mediated peroxymonosulfate activation to degrade 2,4-dichlorophenol. Results from degradation experiments revealed that the catalytic efficiency of the prepared nitrogen-doped biochar was approximately 37.8 times higher than that of the undoped biochar. Quenching experiments combined with Electron paramagnetic resonance (EPR) analysis illustrated that the generated singlet oxygen (1O2) and superoxide anion radical (O2•-) were the main reactive oxidative species that dominated the target organics removal processes. This work will provide a theoretical basis for expanding the practical application of nitrogen-doped biochar to remediate water pollution via peroxymonosulfate activation.

Extraordinary thermoelectric performance, thermal stability and mechanical properties of n-type Mg3Sb1.5Bi0.5 through multi-dopants at interstitial site

Mg3Sb2-based thermoelectric materials have attracted much interest since the discovery of their excellent n-type thermoelectric performance with excess Mg content and proper dopant. Herein, we proposed a doping diagram for Mg3Sb2-based material in a binary parameters space of electronegativity difference and atomic radius difference of extrinsic elements with Mg atom. Based on this doping diagram, we designed a multiple interstitial doped TMx:Mg3Sb1.5Bi0.5 (TM = CrMnFeCoCu) material, and achieved a high dimensionless figure of merit value of 0.76 at room temperature and 1.83 at 500 °C, respectively. The multiple interstitial dopants significantly suppress the formation of Mg vacancy, which is of great importance in protecting the electrical transport channel and improving the thermal stability. Besides, the mechanical properties are also enhanced due to the random distribution of elements in the matrix, impeding the migration of dislocations. Our work verifies the benefits of maximized sub-lattice disordering through the multi-elements doping strategy in the Mg3Sb1.5Bi0.5 material.

Solid solution strengthening and damping capacity of Mg−Ga binary alloys

The mechanical behaviors and damping capacities of the binary Mg−Ga alloys with the Ga content ranging from 1 to 5 wt.% were investigated by means of optical microscope (OM), scanning electron microscope (SEM), X-ray diffraction (XRD), hardness test, tensile test and dynamic mechanical analyzer (DMA). The hardness (HV0.5) increases with the increase of Ga content, which can be described as HV0.5=41.61+10.35c, and the solid solution strengthening effect Δσs of the alloy has a linear relationship with cn, where c is the molar fraction of solute atoms and n=1/2 or 2/3. Ga exhibits a stronger solid solution strengthening effect than Al, Zn or Sn due to the large atomic radius difference and the modulus mismatch between Ga and Mg atoms. The addition of Ga makes the Mg−Ga alloys have better damping capacity, and this phenomenon can be explained by the Granato−Lücke dislocation model. The lattice distortion and the modulus mismatch generated because of the addition of Ga increase the resistance to motion of the dislocation in the process of swinging or moving, and thus the better damping capacity is acquired.

Cocktail effect on RT5-type (R = rare earth, T = 3d transition metal) high entropy intermetallic compounds

The alloys with normal compositions of (Sm1/2Ce1/2)(Co1/3Cu1/3Ni1/3)5, (Sm1/2Pr1/2)(Co1/3Cu1/3Ni1/3)5, (Sm1/2Nd1/2)(Co1/3Cu1/3Ni1/3)5, (Sm1/3Ce1/3Pr1/3)(Co1/3Cu1/3Ni1/3)5, and (Sm1/3Ce1/3Nd1/3)(Co1/3Cu1/3 Ni1/3)5 are designed by mixing RCo5, RNi5, and RCu5 for studying their cocktail effects. These designed alloys are prepared by vacuum Arc melting technology. Their single-phase characteristics are experimentally confirmed by X-ray diffraction and scanning electron microscope with energy dispersive spectrum, and also theoretically confirmed by the reported single-phase formation rule of high entropy alloys: atomic radius difference within 6%, nonpositive mixing enthalpy, and high configuration entropy above 1.50R. The designed alloys are suggested to be the high entropy intermetallic compounds due to their single-phase characteristics and high configuration entropy. The magnetic cocktail effect is observed in magnetic measurements. These intermetallic compounds show low-temperature magnetic transition and field-induced ferromagnetic characteristics. The cocktail effect is suggested to be modulated by the spins with random directions at rare earth and transition metal sublattices caused by mixture of the multiple individual RCo5, RNi5, and RCu5 intermetallic compounds.

Interface charge induced self-assembled (Co(OH)2)4@La(OH)3 heterojunction derived from Co4-MOF@La(HCO2)3 to boost oxygen evolution reaction

Interface engineering as an effective material modification method can regulate local corresponding interfacial geometry and electronic structures, thus enabling a higher intrinsic activity for the oxygen evolution reaction (OER). Herein, we carefully designed p-p heterojunction precursor Co4-MOF@La(HCO2)3 with internal electric field through electrostatic adherence, which then in-situ transformed into p-p type heterojunction electrocatalyst (Co(OH)2)4@La(OH)3 under KOH activation strategy. The one-step in-situ conversion of (Co(OH)2)4@La(OH)3 generated the interface with significant difference in metal atomic radius and exhibits fascinating nanostructures, which enhances the specific surface area and increases the number of active sites compared with the parent material. Impressively, the obtained material (Co(OH)2)4@La(OH)3 demonstrates satisfying electrocatalytic activity in OER with a low overpotential of only 233 mV to reach a current density of 20 mA cm−2, and excellent stability for 50 h at 10 mA cm−2 in alkaline medium. In-situ Raman technique indicates that multivalent Co centers are the true active sites during the OER process. Based on density functional theory (DFT) calculation results, La atoms possess empty d orbitals, which are beneficial to facilitate charge transfer from Co to La at the heterojunction interface. Meanwhile, the introduction of La atoms changes the coordinated environment around the adjacent atoms at the interface, which induces the upshift of the d-band center for Co atoms and increases the binding strength of the adsorbed oxygen intermediate.

A Strategic Design Route to Find a Depleted Uranium High-Entropy Alloy with Great Strength

The empirical parameters of mixing enthalpy (ΔHmix), mixing entropy (ΔSmix), atomic radius difference (δ), valence electron concentration (VEC), etc., are used in this study to design a depleted uranium high-entropy alloy (HEA). X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were used to assess the phase composition. Compression and hardness tests were conducted to select alloy constituents with outstanding mechanical properties. Based on the experimental results, the empirical criteria of HEAs are an effective means to develop depleted uranium high-entropy alloys (DUHEAs). Finally, we created UNb0.5Zr0.5Mo0.5 and UNb0.5Zr0.5Ti0.2Mo0.2 HEAs with outstanding all-round characteristics. Both alloys were composed of a single BCC structure. The hardness and strength of UNb0.5Zr0.5Mo0.5 and UNb0.5Zr0.5Ti0.2Mo0.2 were 305 HB and 1452 MPa, and 297 HB and 1157 MPa, respectively.

The microstructure and properties of Fe55Cr15Ni(30-x)Nbx eutectic high-entropy alloys

The emergence of eutectic high entropy alloys (EHEAs) provides new insights for the design of the next generation structural alloys. In this paper, a set of low-cost Co-free Fe55Cr15Ni(30-x)Nbx (x = 0, 3, 6, 9, 12 and 15 at.%) EHEAs was successfully designed and prepared by vacuum arc melting. With the increase of Nb content, the solidification structure of the EHEAs change from single-phase FCC (x = 0) to divorced eutectic structure (x = 3) containing FCC and Laves phase, hypoeutectic structure (x = 6 and 9) and eventually becomes hypereutectic structure (x = 12 and 15). The FCC phase is rich in Fe, Cr and Ni, and the Laves phase is rich in Nb. The addition of Nb result in the increase of the volume fraction of the hard Laves phase which improved the room temperature strength. Solid solution strengthening and second phase strengthening are the main factors affecting the properties of the alloys. In this study, Fe55Cr15Ni21Nb9 alloy shows the best comprehensive mechanical properties, the compressive fracture strength, fracture strain and yield strength are 1216 MPa, 32% and 749 MPa, respectively. Phenomenologically, when the Nb content is in the range of 0–15 at.%, the yield strength of the alloy is a function of the Nb content: σ0.2=550×ex/15.81−256. For (Co)CrFeNi-based high-entropy alloys, a new phase prediction criterion is proposed in this paper. When the d-orbital energy level of the alloy is Md ≤ 0.92, the atomic radius difference is δ ≤ 2.88 or the mixing enthalpy meets −4.16≤ΔHmix≤0, single-phase FCC will be formed. If this is not the case, the FCC + TCP phase will be formed.

Effect of Alkaline Earth Metal on AZrOx (A = Mg, Sr, Ba) Memory Application

Zr can be stabilized by the element selected, such as Mg-stabilized Zr (MSZ), thus providing MSZ thin films with potentially wide applications and outstanding properties. This work employed the element from alkaline earth metal stabilized Zr to investigate the electrical properties of sol–gel AZrOx (A = alkaline earth metal; Mg, Sr, Ba) as dielectric layer in metal-insulator–metal resistive random-access memory devices. In addition, the Hume–Rothery rule was used to calculate the different atomic radii of elements. The results show that the hydrolyzed particles, surface roughness, and density of oxygen vacancy decreased with decreased difference in atomic radius between Zr and alkaline earth metal. The MgZrOx (MZO) thin film has fewer particles, smoother surface, and less density of oxygen vacancy than the SrZrOx (SZO) and BaZrOx (BZO) thin films, leading to the lower high resistance state (HRS) current and higher ON/OFF ratio. Thus, a suitable element selection for the sol–gel AZrOx memory devices is helpful for reducing the HRS current and improving the ON/OFF ratio. These results were obtained possibly because Mg has a similar atomic radius as Zr and the MgOx-stabilized ZrOx.

Revised Semiempirical Approach to Predict the Occurrence of Twinning in Titanium Alloys.

A revised semiempirical approach, considering the average values of the valence electron to atom ratio (e/a̅) and a difference in atomic radii of alloying element/s and the base element (Δr̅), is proposed to predict the twin formation in titanium alloys. The revised e/a̅ versus Δr̅ diagram is plotted, considering the reported results of 90 titanium alloys fabricated using various processing methods. A new twin/slip boundary has been plotted and recommended based on the revised e/a̅ versus Δr̅ diagram. The conventional maximum limit reported for the twinning in titanium alloys is e/a̅ = 4.20; however, it has been found that twinning in titanium alloys is possible up to the e/a̅ of 4.30.

First-principles analysis of the grain boundary segregation of transition metal alloying elements in γFe

In this study, first-principles calculations were carried out for the first time to systematically investigate the grain boundary segregation of transition metal alloying elements (Ti, V, Cr, Mn, Co, Ni, Cu, Nb, and Mo) in paramagnetic γFe and its dependence on the grain boundary character. The segregation energies of each element and site were comprehensively calculated for nine [001] symmetric tilt grain boundary models with Σ values from 5 to 41; the paramagnetic state was simulated by the antiferromagnetic double-layer (AFMD). By calculating the effective segregation energy for each grain boundary model from the obtained segregation energies, the grain boundary segregation behavior for each alloying element and its dependence on the grain boundary character were investigated. The segregation energy of transition metal elements is dominated by the Voronoi volume of Fe at the segregation site and arises from the elastic energy derived from the difference in atomic radii between the host and solute metals. Ti, Cu, Nb, and Mo have negative effective segregation energies (indicating a tendency toward segregation) at all investigated grain boundaries, and the absolute values of the effective segregation energy increase in the order of Cu < Mo < Ti < Nb in all of the grain boundary models. In contrast, the sign of the effective segregation energies for V, Ni, and Co changes depending on the grain boundary, and the effective segregation energies for Cr and Mn are positive at all grain boundaries. These results corresponded well with the experimental results. The results obtained in this study provide important basic data for the material design of high-strength steels and are useful for understanding the effects of alloying elements in γFe.

Structure and Physical Properties of Cast and Splat-Quenched CoCr0.8Cu0.64FeNi High Entropy Alloy

The article investigates the structure and physical properties of the multicomponent high-entropy alloy CoCr0.8Cu0.64FeNi in the cast and quenched state. The composition of the alloy under study is analyzed using the criteria available in the literature for predicting the phase composition of high-entropy alloys. These parameters are based on calculations of the entropy and enthalpy of mixing and also include the concentration of valence electrons, the thermodynamic parameter Ω, which takes into account the melting point, entropy of mixing, and enthalpy of mixing. Another important parameter is the difference in atomic radii between the alloy components δ. Cast samples of the CoCr0.8Cu0.64FeNi alloy of nominal composition were prepared on a Tamman high-temperature electric furnace in an argon flow using a copper mold. The weight loss during the manufacture of ingots did not exceed 1%, and the average cooling rate was ~ 102K/s. Thereafter, the cast ingot was remelted, and films were obtained from the melt. The splat quenching technique used in this work consisted of the rapid cooling of melt droplets when they collide with the inner surface of a rapidly rotating (~ 8000 rpm) hollow copper cylinder. The cooling rate, estimated from the film thickness, was ~ 106 K / s. X-ray structural analysis was performed on a DRON-2.0 diffractometer with monochromatic Cu Kα radiation. Diffraction patterns were processed using the QualX2 program. The magnetic properties of the samples were measured using a vibrating sample magnetometer at room temperature. The microhardness was measured on a PMT-3 device at a load of 50 g. In accordance with theoretical predictions confirmed by the results of X-ray diffraction studies, the structure of the alloy, both in the cast and in the quenched state, is a simple solid solution of the FCC type. The lattice parameters in the cast and liquid-quenched states are 0.3593 nm and 0.3589 nm, respectively. Measurements of the magnetic properties showed that the CoCr0.8Cu0.64FeNi alloy can be classified as soft magnetic materials. In this case, quenching from a liquid state increases the coercivity. On quenched samples, increased microhardness values were also obtained. This can be explained by internal stresses arising during hardening.

Machine learning assisted prediction of the Young\u2019s modulus of compositionally complex alloys

We identify compositionally complex alloys (CCAs) that offer exceptional mechanical properties for elevated temperature applications by employing machine learning (ML) in conjunction with rapid synthesis and testing of alloys for validation to accelerate alloy design. The advantages of this approach are scalability, rapidity, and reasonably accurate predictions. ML tools were implemented to predict Young’s modulus of refractory-based CCAs by employing different ML models. Our results, in conjunction with experimental validation, suggest that average valence electron concentration, the difference in atomic radius, a geometrical parameter λ and melting temperature of the alloys are the key features that determine the Young’s modulus of CCAs and refractory-based CCAs. The Gradient Boosting model provided the best predictive capabilities (mean absolute error of 6.15 GPa) among the models studied. Our approach integrates high-quality validation data from experiments, literature data for training machine-learning models, and feature selection based on physical insights. It opens a new avenue to optimize the desired materials property for different engineering applications.

The formation of sigma phase in the CoCrFeNi high-entropy alloys

The as-cast CoCrFeNi high-entropy alloys show simple FCC structure and outstanding deformation ability at room temperature. Respectively, after 50% of deforming at room temperature and annealing at intermediate temperature range of 600 °C–800 °C for 2 h, CoCrFeNi alloys still show simple-phase FCC structure. It is noteworthy that CoCrFeNi high-entropy alloys can’t be strengthened by means of annealing, while deformation is an effective way to strengthen the alloys. It is investigated that the formation of sigma (σ) phase in high-entropy alloys is closely related to the difference of atomic radius (δ), the concentration of valence electron (VEC) and paired sigma-forming element (PSFE) content, and PSFE plays an crucial role. When PSFE > 40 at.%, 6.75 ≤ VEC ≤ 7.86, 4.0 ≤ δ ≤ 7.2, σ phase is prone to form in high-entropy alloys. In addition, alloying and processing route are two important factors that affect the sigma-formation in CoCrFeNi high-entropy alloys.

Glass-forming ability of Ni-Zr-Al alloys: the interplay of thermodynamic and geometric factors

ABSTRACT Despite decades of intensive rehearses, we still lack robust and physically clear methods to discover new metallic alloys with high glass-forming ability (GFA). Different empirical criteria proposed to estimate GFA have limited applicability. Here we address the impact of thermodynamic and geometric factors on GFA of Ni-Zr-Al alloys. Using the ideal associated solution model, we calculated the Gibbs energy and the mixing enthalpy of the system and compared the results with available experimental and theoretical data. The results show that the model used is a good approximation for calculating the thermodynamic properties of liquid alloys if both binary and ternary compounds are explicitly taken into account. However, we conclude that it is hardly possible to address GFA of Ni-Zr-Al alloys using only thermodynamic properties. We test a few different criteria, proposed in the literature, and show that they also fail to explain GFA in the system. Then, we propose new parameters based on Gibbs mixing energy and effective difference in atomic radii, which allows localising the composition domain corresponding to the best GFA in Ni-Zr-Al alloys. Our findings open up the prospects to develop reliable theoretical methods for discovering new metallic glasses.

Vibrational properties of High Entropy Alloy based metal hydrides probed by inelastic neutron scattering

The vibrational properties of several High Entropy Alloy (HEA) based metal hydrides are investigated by inelastic neutron scattering (INS). HEAs have recently emerged as a new type of materials with a wide range of intriguing properties and potential applications such as hydrogen storage. The special properties of HEAs are believed to originate from the disordered lattice and internal strain that is introduced from the differences in atomic radii. This makes HEA hydrides provide an intriguing situation for the local H coordination, of several different transition metals. INS spectra were collected on a series of HEA-based metal hydrides starting with TiVNbHx and subsequently adding Zr and Hf to increase the atomic size mismatch. A general feature of the spectra are the optical peaks centered around an energy loss of 150 meV that can be attributed to hydrogen vibrations in a tetrahedral environment. Upon the addition of Zr and Hf, a shoulder appears on the optical peak at lower energy transfers that after comparison with in silico calculated INS spectra is indicative of hydrogen also occupying octahedral sites in the structure.

Study on strengthening effects of Zr-Ti-Nb-O alloys via high throughput powder metallurgy and data-driven machine learning

Multi-principal elements alloys (MPEAs) have been attracted extensive attention in industry due to their extraordinary properties. However, owning to their large degree of freedom in composition design, finding the principal influence factors of the material properties and further coordinating a desirable combination of conflicting properties is always a challenge. In this respect, we have developed a strategy on studying the MPEAs for its composition design in a certain mechanical property by high throughput preparation of powder metallurgy and by machine learning. We chose Zr-Ti-Nb-O alloys as target materials. To unveil key features that mainly influence the mechanical properties, models selection, featuresscreening, and further features importance ordering were performed. The results indicate that the strength and plasticity are dominated by Λ parameter, difference of atomic radius, difference of shear modulus, etc. The prediction error for the strength and plasticity can reach to below 10% and 16%, respectively. According to analysis of the key features, a strength model is modified and used for evaluating the contributions of solid solution strengthening among principle and trace elements. The strategy proposed here will be applicable on element selections for a large variety of material property modulations in the MPEAs prepared by powder metallurgy.