Electronegativity Difference Research Articles

Cleavage of Homonuclear Chalcogen-Chalcogen Bonds in a Hybrid Platform in Response to X-ray Radiation Potentiates Tumor Radiochemotherapy.

Chalcogens are used as sensitive redox-responsive reagents in tumor therapy. However, chalcogen bonds triggered by external ionizing radiation, rather than by internal environmental stimuli, enable site-directed and real-time drug degradation in target lesions. This approach helps to bypass chemoresistance and global systemic toxicity, presenting a significant advancement over traditional chemoradiotherapy. In this study, we fabricated a hybrid monodisperse organosilica nanoprodrug based on homonuclear single bonds (disulfide bonds (S-S, approximately 240 kJ/mol), diselenium bonds (Se-Se, approximately 172 kJ/mol), and tellurium bonds (Te-Te, 126 kJ/mol)), including ditelluride-bond-bridged MONs (DTeMSNs), diselenide-bond-bridged MONs (DSeMSNs) and disulfide-bond-bridged MONs (DSMSNs). The results demonstrated that differences in electronegativities and atomic radii influenced their oxidation sensitivities and reactivities. Tellurium, with the lowest electronegativity, showed the highest sensitivity, followed by selenium and sulfur. DTeMSNs exhibited highly responsive cleavage upon exposure to X-rays, resulting in oxidation to TeO32-. Furthermore, chalcogen-hybridized organosilica was loaded with manganese ions (Mn2+) to enhance the release of Mn2+ during radiotherapy, thereby activating the the stimulator of interferon genes (STING) pathway and enhancing the tumor immune response to inhibit tumor growth. This investigation of hybrid organosilica deepens our understanding of chalcogens response characteristics to radiotherapy and enriches the design principles for nanomedicine based on prodrugs.

Lightweight single-phase Al-based complex concentrated alloy with high specific strength

Developing light yet strong aluminum (Al)-based alloys has been attracting unremitting efforts due to the soaring demand for energy-efficient structural materials. However, this endeavor is impeded by the limited solubility of other lighter components in Al. Here, we propose to surmount this challenge by converting multiple brittle phases into a ductile solid solution in Al-based complex concentrated alloys (CCA) by applying high pressure and temperature. We successfully develop a face-centered cubic single-phase Al-based CCA, Al55Mg35Li5Zn5, with a low density of 2.40 g/cm3 and a high specific yield strength of 344×103 N·m/kg (typically ~ 200×103 N·m/kg in conventional Al-based alloys). Our analysis reveals that formation of the single-phase CCA can be attributed to the decreased difference in atomic size and electronegativity between the solute elements and Al under high pressure, as well as the synergistic high entropy effect caused by high temperature and high pressure. The increase in strength originates mainly from high solid solution and nanoscale chemical fluctuations. Our findings could offer a viable route to explore lightweight single-phase CCAs in a vast composition-temperature-pressure space with enhanced mechanical properties.

Sulfur Modified Copper Nitride for Electrochemical CO2 Reduction Reaction

Metallic copper has been attracted attention as efficient catalyst for electrochemical CO2 reduction reaction (CO2RR). However, the activity of the catalyst with a single adsorption site is limited by the imbalance of the intermediate binding energy, so-called “scaling relationship”. [1] Therefore, it is crucial to break the scaling relationship between reaction intermediates in order to increase product selectivity and lower overpotential. One of the candidates to overcome this scaling relationship is metal sulfide. According to the computational study, since sulfur atoms work as an adsorption site, metal sulfide is expected to be a suitable catalyst for CO2RR with multiple adsorption sites.[2] In addition, surface modification by sulfur is also effective approach to enhance product selectivity in CO2RR. Increase of formate (HCOO-) selectivity by sulfur introduction on Cu has been reported in some previous reports.[3]-[5] On the other hand, the repulsion between the oxygen lone pair electrons of the CO2 molecule and the electronic clouds of the surface sulfur atoms become an obstacle on CO2RR.[6] A potential solution to this problem is the construction of sulfide-nitride composite. Because of the difference in electronegativity between nitrogen and metal or sulfur, it is considered that the electronic structure of the metal sulfide is altered to reduce the repulsion between oxygen and sulfur.[7] Based on these backgrounds, it is expected that the CO2RR activity of copper nitride (Cu3N) will be enhanced by sulfur introduction.Here, sulfur modified Cu3N with different amount of sulfur were synthesized by reflux method with some modification of previously reported method.[8] X-ray diffraction pattern and SEM-EDX elemental analysis result indicate that the sulfur ratio increases and copper sulfide (Cu2S) crystal phase appears with the amount of sulfur source precursor. CO2RR activity was evaluated in 0.1M KHCO3 electrolyte, and volcano trend was identified between the amount of sulfur and methane selectivity. Among all the catalysts including pure Cu3N and Cu2S which were synthesized by the same method, 4.2 mol% sulfur containing Cu3N showed the highest methane faradaic efficiency (41.4 %). This faradaic efficiency is more than 10 times higher than that of Cu3N (0.48 %) and Cu2S (1.3 %). This finding offers valuable insights into the sulfur role on the modified catalyst.

(Invited) Defect Photoluminescence Generation in Boron Nitride Nanotubes by Chemical Functionalization Approaches

Boron nitride nanotubes (BNNTs) are structural analogues of carbon nanotubes (CNTs). They have nanocylindrical structures composed of rolled-up hexagonal boron nitride (h-BN) sheets. The BN framework consists of alternately connecting boron and nitrogen atoms with sp2 hybridization. Therein, a strong covalent bond with an ionic character is formed due to their electronegativity difference. Accordingly, BNNTs exhibit unique properties such as high mechanical strength, thermal stability, and a wide bandgap semiconducting feature [1]. The large bandgap (ca. 6 eV) is less dependent on tube diameters and chiralities, and optical absorption and emission for pristine tubes occur in deep UV regions (around 200 nm) based on the band edge transition. In typical BNNT samples, however, atomic vacancies in the BN framework are reported to provide longer wavelength photoluminescence (PL) in UV–vis regions [2].To date, chemical functionalization of single-walled CNTs (SWCNTs) have been developed to create luminescent defects emitting red-shifted and bright near-infrared PL [3-6]. In this study, we use the chemical functionalization method to produce luminescent defects in BNNTs [7].A reductive alkylation reaction for BNNTs was conducted using sodium naphthalenide and 1-bromohexane to synthesize hexylated BNNTs (h-BNNTs). In a PL spectrum of h-BNNTs, PL peaks appeared at 334 and 413 nm, which were not observed for unmodified BNNTs. X-ray photoelectron spectroscopy revealed that the hexyl group was covalently attached on the boron site of BNNTs, by which sp3 hybridized boron atoms were partly formed in the BN network as defects. The covalent attachment of the hexyl group was also confirmed by atomic-resolution transmission electron microscope observations. Chemical reaction conditions were found to be a key factor for the emission wavelength variations of the resultant defect PL. Therefore, it is revealed that the luminescent defect formation in BNNTs is achieved based on the chemical functionalization approach. The functionalized BNNTs would be applicable to advanced optical applications such as quantum light sources.[1] D. Golberg et al. ACS Nano,4, 2979 (2010). [2] L. Museur et al. J. Appl. Phys., 118, 084305 (2015). [3] T. Shiraki et al. Acc. Chem. Res., 53, 1846 (2020). [4] B. Gifford et al. Acc. Chem. Res., 53, 1791 (2020). [5] A. H. Brozena et al. Nat. Rev. Chem. 3, 375 (2019). [6] J. Zaumseil. Adv. Opt. Mater. 10, 2101576 (2022). [7] T. Shiraki et al. Chem. Lett. 52, 44 (2023). Figure 1

Metal V doping optimizes the binding affinity of CuCoO2 with OH- contributes to efficient oxygen evolution reaction

CuCoO2 has been used in various catalytic fields because of its unique structure, but its oxygen evolution reaction (OER) performance still needs to be further improved. The current study did not delve into the effect of reaction intermediates on the OER performance of CuCoO2. Therefore, in this study, metal V was introduced to regulate the electronic structure of CuCoO2 and optimize the combination of catalyst and OER intermediates, thus promoting the improvement of OER performance of CuCoO2. In this study, V doped CuCoO2 nanocrystals were successfully synthesized through solvothermal method. The metal V influences the OER performance of CuCoO2 by modulating the crystal structure of CuCoO2. The electronegativity of V is lower than that of Cu, so V can be used to optimize the binding affinity of CuCoO2 with OH- by adjusting dz2 orbitals (O-Co). The electrochemical test results show that 1.5 at% V doped CuCoO2 (CVCO-1.5) yields excellent catalytic performance (η10 = 353 mV, Tafel slope = 69 mV dec−1). The main reason is that V promotes the formation of oxygen vacancies (VO) in CuCoO2 and optimizes the adsorption of reaction intermediates by CuCoO2, thus reducing energy barriers of the reaction. In this work, based on the difference of electronegativity between metals, the binding affinity of the catalysts for OH- is optimized by simple solvothermal method, which can be used as a reference for other delafossite oxide materials and even metal oxide materials.

Investigating the impact of alloying elements on hydrogen diffusion in Ti-based alloys via first-principles calculations

The diffusion of hydrogen in Ti-based alloys can lead to localized degradation of mechanical properties, resulting in hydrogen embrittlement. Therefore, identifying alloying elements that impede hydrogen diffusion is a crucial approach to mitigating hydrogen embrittlement and stress corrosion in Ti-based alloys. Utilizing first-principles calculations, we investigated the effects of 33 alloying elements on hydrogen diffusion in Ti-based alloys, including diffusion barriers and coefficients. Our findings demonstrate that elements such as Al, Ga, Si, and Zn increase the hydrogen diffusion barriers and decrease the diffusion coefficients in Ti-based alloys, thereby mitigating hydrogen embrittlement. It is revealed that the difference of electronegativity of Al, Si, Au, Ag, Pd, Ir, Zn, and Cu affects the hydrogen atom trapping ability. It also sheds light on strategies to mitigate hydrogen embrittlement in Ti-based alloys. This insight highlights their significant role in hindering the movement of hydrogen atoms within the alloys.

Modulation of Polarization in Sliding Ferroelectrics by Introducing Intrinsic Electric Fields.

The emergence of sliding ferroelectricity facilitates low-barrier ferroelectrics in two-dimensional materials, while limited electric polarizations impede practical applications. Herein, we propose an effective strategy to enlarge the polarization by introducing an intrinsic electric field, exemplified by Janus transition metal dichalcogenides (TMDs) with the first-principle calculations. The intrinsic electric field is introduced and regulated by leveraging the electronegativity differences among chalcogens. An improved polarization is achieved in the Janus TeMoS bilayer with a polarization of 1.18 pC/m, a 65% enhancement compared to normal TMD bilayers. Through differential charge density analysis, the inner mechanism is attributed to the effects of intrinsic electric fields on charge redistribution. Furthermore, the feasibility of polarization reversal is determined by evaluating switching barriers and the responses under an electric field. The provided proposal is applicable and available for broader systems and will pave the way for the development of novel electronic devices.

Designed inorganics doped gel electrolyte with enhancing ion transfer and diffusion effects for flexible interdigitated supercapacitors

Electrolyte enhancement strategy becomes a promising route to improve flexible interdigitated miniaturized supercapacitors (IMSCs) performance due to the less mass loading of electrode materials on interdigitated electrodes. Herein, we develop a flexible polyvinyl alcohol/KOH (PVA/KOH) gel electrolyte with homogeneous BN-PDA (polydopamine modified boron nitride nanosheets) doping for enhancing energy storage of IMSCs, in which the conductivity is up to 112.1 mS cm−1 with excellent mechanical strength and heat stability. The ionicity of BN-PDA caused by electronegativity difference between B and N atoms significantly facilitates KOH transfer in PVA gel and diffusion in electrode diffuse layer by rapping-pairing effect. Furthermore, the different phase transition behavior of BN-PDA and PVA in water provides additional ions transmission pathways and effectively disperses external forces. With such excellent electrolytes, ultra-high energy density (14.7 μWh cm−2) at a high power density (420 μW cm−2) has been achieved for IMSCs. Moreover, the capacitance of IMSCs can always be maintained at a very high level during the long-term charge and discharge process. Our work suggests a feasible pathway to design inorganic fillers uniformly modified gel electrolyte with high conductivity and increased energy storage capacity of IMSCs as well as other flexible energy storage devices.

Investigation of kesterite to stannite phase transition and band gap engineering in Cu2Zn1-xCoxSnS4 thin films prepared by sol-gel spin coating

In this study, the Cu2Zn1-xCoxSnS4 (CZn1-xCoxTS) films with partial cation substitution of cobalt are synthetized by sol gel spin coating, followed by sulfurization treatment. The incorporation of cobalt cation in the CZTS crystalline lattice as well as the phase transition from kesterite to stannite were confirmed by the X-ray diffraction (XRD) and Raman spectroscopy data. The XRD pattern shows peak-shifting toward higher 2θ by increasing the Co concentration, indicating a decrease in lattice parameters. The red shift of Raman peaks by increasing x from 0 to 0.6, confirms the phase transition. The CZn1-xCoxTS morphology was observed by scanning electron microscopy, showing large grain size as x increases and a good distribution of elements for all films. X-ray photoelectron spectroscopy was employed to study the valence of cations/anions and to probe the chemical bonds. The optical band gap showed a parabolic behavior versus the molar ratio Co/(Co + Zn), this deviation from Vegard’s law being induced by the difference in electronegativity between cobalt and zinc. The pure CZTS has a band gap of 1.47 eV, while for CZn0.6Co0.4TS the gap is 1.17 eV, which indicates that the incorporation of cobalt cation produces a red-shift of the band to band transition energy.

Machine learning-assisted prediction and interpretation of electrochemical corrosion behavior in high-entropy alloys

In this study, machine learning (ML) models were successfully employed to predict the short-term electrochemical corrosion behavior of high-entropy alloys (HEAs) based on their chemical compositions. Considering the vast compositional space of HEAs, which restricts the development of corrosion-resistant HEAs, and the lack of non-destructive methods to qualitatively assess their corrosion resistance, this work represents a significant advancement in the field. The “three-step” method was applied to select the optimal feature set from 38 features, and six ML regression models were trained and compared. The eXtreme Gradient Boosting (XGBoost) and Gradient Boosting Decision Tree (GBDT) algorithms demonstrated the highest predictive accuracy (R2 = 81.02 % and 84.64 %, respectively) among the six algorithms. The model’s robust generalization capabilities were confirmed through validation on an additional dataset. Moreover, the interpretability of the model was enhanced by employing two analysis methods, which revealed that pH as an environmental factor, electronegativity difference and average electronegativity as empirical parameters, and the concentrations of Cr and Cu as compositional parameters have the most significant impact on the corrosion resistance of HEAs. The proposed methodology and framework have the potential to optimize alloy composition, facilitating the design and development of new corrosion-resistant HEAs.

Stimulating Electron Delocalization of Lanthanide Elements through High-Entropy Confinement to Promote Electrocatalytic Water Splitting.

High-entropy alloys (HEAs) have aroused extensive attention in the field of catalysis. However, due to the integration of multiple active sites in HEA, it exhibits excessive adsorption behavior resulting in difficult desorption of active species from the catalyst surfaces, which hinders the catalytic efficiency. Therefore, adjusting the adsorption strength of the active site in HEA to enhance the catalytic activity is of great importance. By introducing rare-earth (RE) elements into the high-entropy alloy, the delocalization of 4f electrons can be achieved through the interaction between the multimetal active site and RE, which benefits to regulate the adsorption strength of the HEA surface. Herein, the RE Ce-modified hexagonal-close-packed PtRuFeCoNiZn-Ce/C HEAs are synthesized and showed an excellent electrocatalytic activity for hydrogen evolution reaction and oxygen evolution reaction with ultralow overpotentials of 4, 7 and 156, 132 mV, respectively, to reach 10 mA cm-2 in 0.5 M H2SO4 and 1.0 M KOH solutions, and the assembled water electrolysis cell only requires a voltage of 1.43 V to reach 10 mA cm-2, which is much better than the performance of PtRuFeCoNiZn/C. Combined with the results of in situ attenuated total reflection infrared spectroscopy and density functional theory (DFT), the fundamental reasons for the improvement of catalyst activity come from two aspects: (i) local lattice distortion of HEA caused by the introduction of RE with large atomic radius induces 4f orbital electron delocalization of RE elements and enhances electron exchange between RE and active sites. (ii) The electronegativity difference between the RE element and the active site forms a surface dipole in HEA, which optimizes the adsorption of the active intermediate by the HEA surface site. This study provides an insightful idea for the rational design of high-performance HEA- and RE-based electrocatalysts.

Luminescence spectra and site-occupation of Eu3+ centres in lithium antimonate LiSbO3 lattice

It is a challenge to accurately determine the exact location of the rare earth ion (RE) in the lattice when there are significant differences in radius, electronegativity and valence between the lattice cation and the corresponding RE activator in a host material. This study presents the findings on the luminescence and site occupancy of Eu3+ emission centers in the lithium antimonate LiSbO3 lattice. The phase-formation, structures, elemental composition, band transition characteristics, luminescence properties, and lifetimes of the Eu3+-doped phosphors were investigated. Eu3+-doped LiSbO3 exhibits a typical 5D0→7F2 red luminescence transition at 613 nm. Site-selective excitation, luminescence, and decay properties at the 7F0→5D0 transition wavelength were measured using a tunable pulsed narrow-band dye laser. Two Eu3+ luminescence centers in LiSbO3 were identified across the temperature range from 10 K to 300 K. The doping of RE(Eu3+) in LiSbO3 consistently occupies two crystallographic positions of Li+ and Sb5+. Furthermore, the probability of RE(Eu3+) ions preferentially occupying the Li+ (M) sites is notably high. The decay curves and luminescence lifetimes of the two Eu3+ centers were determined. Drawing from the experimental data, we discuss the potential defects induced by Eu3+ doping in LiSbO3 and the mechanism of charge compensation. These results could be instrumental in the advancement of new RE-activated luminescent materials or serve as a reference for investigating the specific positioning of RE ions within a phosphor lattice.

Nature of the bond in intermetallic compounds

By studying 398 binary compounds crystallizing in five different crystal structures, it is shown that atomic radii of the elements RA and RB change to reach a constant radius ratio rA/rB(≡ϒ) in a cubic system. In systems of lower symmetry, a range of ϒ values, each corresponding to a certain axial ratio, is possible. Accurate charge values on atoms in solids are derived from the experimental internal radii rA and rB, using Shannon’s compilation of radii versus charge states for elements. It is found, for the first time, that charge transfer and radii change reverse their direction at the ϒ point. Electronegativity difference relative to its value at the ϒ point is recognized to correctly predict the charge transfer and radii changes with RA/RB. The deduced electronic structure of solids, based on spherical ions carrying partial charges, confirms that the metallic atom-pair bond is a resonating polar covalent bond. Identification of the number of electrons that contribute to cohesion and electrical conduction individually, allows successful prediction of electrical conductivity variation for transition metals and p-elements in the periodic table. From a knowledge of accurate valence of elements and of charge on the atoms, variation in the 197Au isomer shift of the gold compounds of CsCl type structure is predicted. The charges on atoms computed using the Quantum Theory of Atoms in Molecules (QTAIM) technique agree with those obtained in our work for compounds belonging to two of the structure types. For compounds belonging to the other three, the charge values obtained by the two methods do not agree. The disagreement correlates to not reckoning the role of the ϒ point. The effect of ϒ point is so fundamental and universal that most physical properties obtained by the secondary processing of primary DFT data, can be influenced by it.

A Review on Binary Alkaline‐Earth Trielides: an Overview of Compositions and Structures, of their Stabilities and Energetics and of Criteria for the Validity of the Zintl‐Concept

AbstractOmitting alloys with a compositional range we present a compilation of binary alkaline earth trielides AExTRy together with results of DFT calculations to estimate total energies and energies of formation in comparison and to analyse the distribution of charges at the atomic positions in a Bader analysis of the electron density. In a comparison of many structures, we furthermore analyse the effect of bonding on this charge distribution and reflect on the real bonding patterns in comparison with our expectations according to the Zintl concept, and we find mechanisms blocking an electron transfer as favoured by the electronegativity differences. We have subjected a variety of structural parameters together with the DFT results to a Principal Component Analysis to explore their relationship which we describe in the form of correlation matrices and biplots. The Zintl rules turn out to be a very slack guideline in rationalizing the structures of these compounds.

Enhanced Thermoelectric Performance in Flexible Sulfur-Alloyed Ag2Se Thin Films.

Flexible thermoelectric generators can directly convert thermal energy harvested from the human body into electricity. The Ag2Se flexible film, a promising material for wearable thermoelectric generators, normally demonstrates an inferior electrical transport property due to its weakened in-plane mobility. In this study, the in-plane electrical transport properties of flexible Ag2Se films were optimized by alloying with additional sulfur. This optimization is achieved by leveraging the differences in elemental electronegativity and the preferred orientation of the Ag2Se films. The sulfur-alloyed Ag2Se thin film, with a nominal ratio of 3 atom %, can reach a maximum mobility of 1150 cm-2 V-1 s-1 at 300 K. So, the optimized room-temperature power factor increases to 1935 μW m-1 K-2. Furthermore, the Ag2Se film alloyed with 3 atom % sulfur exhibits excellent flexibility even after 1000 bending cycles with a radius of 5 mm, characterized by a relative resistance increment of less than 3%. In addition, the corresponding π-type flexible thermoelectric generator possesses a maximum power density of 51 W m-2 at a temperature difference of 50 K.

High-Throughput Screening of All-d-Metal Heusler Alloys for Magnetocaloric Applications.

Due to their versatile composition and customizable properties, A2BC Heusler alloys have found applications in magnetic refrigeration, magnetic shape memory effects, permanent magnets, and spintronic devices. The discovery of all-d-metal Heusler alloys with improved mechanical properties compared to those containing main group elements presents an opportunity to engineer Heusler alloys for energy-related applications. Using high-throughput density-functional theory calculations, we screened magnetic all-d-metal Heusler compounds and identified 686 (meta)stable compounds. Our detailed analysis revealed that the inverse Heusler structure is preferred when the electronegativity difference between the A and B/C atoms is small, contrary to conventional Heusler alloys. Additionally, our calculations of Pugh ratios and Cauchy pressures demonstrated that ductile and metallic bonding are widespread in all-d-metal Heuslers, supporting their enhanced mechanical behavior. We identified 49 compounds with a double-well energy surface based on Bain path calculations and magnetic ground states, indicating their potential as candidates for magnetocaloric and shape memory applications. Furthermore, by calculating the free energies, we propose that 11 compounds exhibit structural phase transitions and suggest isostructural substitutions to enhance the magnetocaloric effect.

Polarization loss in rutile TiO2 doped with acceptor ions for microwave absorption

With an increase in electromagnetic (EM) pollution, inducing polarization loss using lattice defects has become one of the main strategies for the design and optimization of a new generation of microwave absorbers. In this study, point defects in TiO2 absorbers are designed and controlled using a sol–gel method. The influences of the electronegativity difference and the ionic valence states of the dopant ions on the microwave absorption (MA) performance of rutile TiO2 composites are investigated. The results show that the defects such as oxygen vacancy (VO∙∙) and Ti3+ can be adjusted continuously at a high-temperature sintering process. Cu2+, which has a larger electronegativity than Ti4+ (Cu2+χ = 1.90 > Ti4+χ = 1.54) promotes the localization of electrons. Furthermore, compared with Ag+, which has a similar electronegativity (Ag+χ = 1.93 ≈ Cu2+χ = 1.90), polyvalent copper ions (Cu2++e→Cu+) enhance the electron-hopping process. The formed electron-pinning defect dipole clusters (TiTi′, VO∙∙, CuTi″, CuTi″′, Ti3+→VO∙∙←Ti3+, Ti3+→VO∙∙←Cu2++e, Cu2++e→Cu+, Ti4++e→Ti3+) produce a stronger polarization relaxation process, which regulates the MA performance of TiO2 absorbers. Therefore, this study provides an essential reference for refining the EM wave attenuation performance of simple oxide absorbers.

Comprehensive improvement of AB2 hydrogen storage alloy: Substitution of rare earth elements for different A-side alloys

Rare earth substitution enhances the activation, absorption/desorption properties of hydrogen storage alloys, a crucial research area. Despite the extensive variety of A-site elements in multicomponent alloys, there remains a scarcity of reports on how to enhance the hydrogen storage capacity of alloys by substituting different elements with rare earth elements at the A-site, which needs to be further explored. In this study, the AB2 type Ti-Mn based hydrogen storage alloy was selected as the research object, and the effect of replacing different elements in the A-position by rare earth elements with equal atomic ratios was systematically analyzed by replacing the hydrogen absorption elements Ti/Zr with the rare earth metal Ce. The result reveals that Ce substitution significantly enhances the hydrogen storage and cyclic performance of the alloys, with Ce substituting for Ti showing superior performance. Theoretical calculations indicate that Ce substitution for Ti in alloys leads to lower formation energy and easier hydrogen absorption than Ce substitution for Zr. Beyond the influence of the Lundin’s theory, this work proposes for the first time that the difference in electronegativity between substituent elements may one of the crucial factors affecting the hydrogen storage performance of alloys. The greater difference in electronegativity may lead to a higher hydrogen storage capacity of the hydrogen storage alloy. This opens a new avenue for research into doping/substitution modifications of hydrogen storage alloy elements. These findings not only enrich the knowledge on element doping modification but offer valuable insights for future research on rare earth-doped modification of hydrogen storage alloys.

Effect of sputtering power and substrate bias on microstructure, mechanical properties and corrosion behavior of CoCrFeMnNi high entropy alloy thin films deposited by magnetron sputtering method

The CoCrFeMnNi high entropy alloy thin films with crystalline (solid solution) structure or amorphous state were fabricated by magnetron sputtering process at different target powers and different substrate bias. Effects of the target power and substrate bias on the characteristics of the CoCrFeMnNi thin films such as microstructures, morphology and surface topography, as well as mechanical properties and corrosion behavior were studied. Phase prediction was calculated by using thermodynamic and kinetic criteria under various deposition conditions. The enthalpy, entropy, δ and Ω parameters, and electronegativity differences influenced the solid solution stability of thin films. These parameters led to the formation of solid solutions with crystalline or amorphous structures under specific limits, which corresponded to the practical XRD and TEM analysis results. Using a substrate bias in the deposition of CoCrFeMnNi thin film changed the amorphous structure to a crystalline (solid solution (BCC + FCC)) at higher target powers (200 and 300 W). On the other hand, the film structure was entirely amorphous at all sputtering target powers without the substrate bias. The mechanical properties, such as hardness, Young's modulus, film strength, and fracture toughness of CoCrFeMnNi thin film, can be enhanced by using the substrate bias and increasing the sputtering power. The potentiodynamic polarization test in 3.5 wt% NaCl aqueous solution indicated that the deposition of CoCrFeMnNi thin films at different sputtering powers and without substrate bias could increase the corrosion resistance of 304 stainless steel substrate. Using the substrate bias of −100 V in the fabrication of CoCrFeMnNi thin film decreased the corrosion current density and increased its polarization resistance.

Tailoring local chemical fluctuation of high-entropy structures in thermoelectric materials.

In high-entropy materials, local chemical fluctuation from multiple elements inhabiting the same crystallographic site plays a crucial role in their unique properties. Using atomic-resolution chemical mapping, we identified the respective contributions of different element characteristics on the local chemical fluctuation of high-entropy structures in thermoelectric materials. Electronegativity and mass had a comparable influence on the fluctuations of constituent elements, while the radius made a slight contribution. The local chemical fluctuation was further tailored by selecting specific elements to induce large lattice distortion and strong strain fluctuation to lower lattice thermal conductivity independent of increased entropy. The chemical bond fluctuation induced by the electronegativity difference had a noticeable contribution to the composition-dependent lattice thermal conductivity in addition to the known fluctuations of mass and strain field. Our findings provide a fundamental principle for tuning local chemical fluctuation and lattice thermal conductivity in high-entropy thermoelectric materials.