Smaller Atomic Radius Research Articles

Синтез самоармованого порошкового матеріалу на основі високоентропійного сплаву

In this work, the formation of a self-reinforced HEA–WC powder material during the mechanical alloying (MA) of a mixture of elemental powders of the W-Fe-Co-Ni system in a planetary ball mill in a gasoline environment was investigated. X-ray diffraction (XRD), microstructural, and energy dispersive spectral (EDS) analysis revealed that after 20 hours of MA of the powders in a carbon-containing medium, a powder material based on a high-entropy alloy was formed. HEA based powder material contains two solid solutions with BCC and FCC crystal structure, as well as a carbide WC phase formed "in-situ" owing to the large negative value of the mixing enthalpy between carbon and tungsten. The “in-situ” formation of WC particles contributes to the enhancement of interfacial bonding with the metal matrix of the HEA. All phase components of the HEA–WC powder material are in the nanostructured state. The particles of the powder material have a close to spherical shape and a bimodal particle size distribution. The powder material consists of fine particles with a size of 1–10 μm and their agglomerates with a size up to 100 μm. The microstructure of the particles consists of the main gray phase of the BCC solid solution, dark spaces of the FCC solid solution and fine WC particles with a size of 0.1 μm to 1 μm evenly distributed in the HEA matrix. High-entropy alloys with the addition of carbon are promising in terms of practical application, because carbon, having a small atomic radius, dissolves as an interstitial element in the crystal lattice of the substitutional solid solutions of the HEA principal elements and, as a result, significantly affects their structure and phase composition, and, therefore, will contribute to the improvement of the mechanical properties of the self-reinforced powder material due to the effects of both solid-solution strengthening by interstitial atoms and the precipitation strengthening by the carbide phase particles.

Effects of Doping on Elastic Strain in Crystalline Ge-Sb-Te.

Phase-change random access memory (PcRAM) faces significant challenges due to the inherent instability of amorphous Ge2Sb2Te5 (GST). While doping has emerged as an effective method for amorphous stabilization, understanding the precise mechanisms of structural modification and their impact on material stability remains a critical challenge. This study provides a comprehensive investigation of elastic strain and stress in crystalline lattices induced by various dopants (C, N, and Al) through systematic measurements of film thickness changes during crystallization. Through detailed analysis of cross-sectional electron microscopy data and theoretical calculations, we reveal distinct behavior patterns between interstitial and substitutional dopants. Interstitial dopants (C and N) generate substantial elastic strain energy (~9 J/g) due to their smaller atomic radii (0.07-0.08 nm) and ability to occupy spaces between lattice sites. In contrast, substitutional dopants (Al) produce lower strain energy (~5 J/g) due to their similar atomic radius (0.14 nm) to host atoms. We demonstrate that N doping achieves higher elastic strain energy compared to C doping, attributed to its preferential formation of Ge-N bonds and resulting lattice distortions. The correlation between dopant properties, structural features, and induced strain energy provides quantitative insights for optimizing dopant selection. These findings establish a fundamental framework for understanding dopant-induced thermodynamic stabilization in GST materials, offering practical guidelines for enhancing the reliability and performance of next-generation PcRAM devices.

Phosphorus Doping Effects on the Optoelectronic Properties of K₂AgAsBr₆ Double Perovskites for Photovoltaic Applications

This work explores the modifications of optoelectronic properties in K₂AgAsBr₆ double perovskites induced by phosphorus doping. First-principles calculations using the CASTEP code with the PBE functional were carried out based on density functional theory (DFT). Our research investigates the electronic structure and optical behavior of the cubic Fm-3m phase of K₂AgAsBr₆, K₂AgAs₀.₈P₀.₂Br₆, and K₂AgAs₀.₆P₀.₄Br₆ to elucidate the impact of progressive phosphorus (P) substitution. P was chosen for its potential to modify the electronic structure due to its smaller atomic radius and different valence orbital energies compared to As. Our results reveal a systematic narrowing of the band gap with increasing P content, from 0.749 eV for the undoped compound to 0.587 eV for K₂AgAs₀.₈P₀.₂Br₆ and 0.424 eV for K₂AgAs₀.₆P₀.₄Br₆. This trend is attributed to the upward shift of the valence band maximum due to the higher energy of P 3p orbitals compared to As 4p orbitals. Analysis of the density of states confirms increased hybridization between P-p and As-p states at the valence band edge. Optical properties, including absorption coefficient, dielectric function, refractive index, and extinction coefficient, demonstrate a consistent red-shift and broadening of spectral features with P doping. Notably, P-substituted compounds exhibit enhanced absorption in the visible light region, with up to a 20% increase in the absorption coefficient at 550 nm for K₂AgAs₀.₆P₀.₄Br₆ compared to the undoped compound. This study reveals that elemental substitution offers a viable route to tailor optical and electronic properties of double perovskites, paving the way for the design of novel materials for next-generation photovoltaic and photoelectric devices.

Optimization of Co4Sb11.5Te0.5 thermoelectric performance through Al filling under high temperature and high pressure

So far, the method of optimizing the thermoelectric properties of skutterudite CoSb3 is usually to achieve a breakthrough in high-properties thermoelectric merit by selecting excellent doping atoms and determining a reasonable percentage of atoms. In this study, we achieved the preparation of small atomic radius Al-filled Co4Sb11.5Te0.5 compounds by high-temperature and high-pressure (HTHP) synthesis methods. The thermoelectric properties of the samples AlxCo4Sb11.5Te0.5 were optimized from two dimensions: synthesis pressures (1.0 GPa, 1.5 GPa, 2.0 GPa) and Al filling concentration (x = 0.1, 0.2, 0.3, 0.5), ultimately achieving effective decoupling of electron-phonon transport properties. The experimental results show that Al doping can optimize the electrical transport properties of materials effectively, rapid synthesis method of HTHP can introduce abundant grain boundaries, diversification of grain sizes, a large number of dislocations and widely distributed nano second phase, etc. These microstructures in bulk materials form a multi-scale phonon scattering network in situ, which can effectively scatter phonons and reduce the lattice thermal conductivity effectively. After optimizing the synthesis pressure and Al filling concentration through orthogonal transformation, the sample Al0.3Co4Sb11.5Te0.5 prepared at a synthesis pressure of 1.5 GPa obtained a minimum lattice thermal conductivity value of 0.88 W m−1 K−1, a maximum power factor of 40.96 μ W cm−1 K−2 and a maximum zT value of 1.18 at 773.15 K.

First-principles study of stability, order and disorder based on an entropy descriptor in noble and ferromagnetic transition metal alloys

Binary alloys AB composed of ferromagnetic metals A (Fe, Co, Ni) and the late 4d−5d noble metals B (Rh, Pd, Ag, Ir, Pt, Au) have been investigated using density functional theory with the generalized gradient approximation to understand the role of magnetism in the stability and the order–disorder transition which has an impact on their physicochemical properties, their applications and their possible implementation as precursors of high-entropy alloys. The enthalpy of formation related to the stability demonstrates that all the alloys are more stable in the ferromagnetic phase than in the nonmagnetic phase. The transition from ordered to disordered phases is quantified using a descriptor which is the standard deviation of the energy spectrum of a set of small nanoalloys with random atomic configurations. The study highlights the fact that the entropy-related descriptor, which is a quantity in determining the formation of a disordered phase as a solid solution or an ordered phase is highly dependent on the atomic environment. Despite the fact that the overall variation of this descriptor is supposed to be unpredictable, there is a noticeable trend showing that the environment-dependent ferromagnetism contributes to a chemical order in alloys and nanoalloys and that this order depends on the atomic radius of the species considered. The results indicate that species with small atomic radii, such as nickel, rhodium or iridium are more likely to form solid solutions than species with larger atomic radii and with more delocalized orbitals.

Effect of Methylammonium Iodide (MACl) on MAPbI3-Based Perovskite UV-C Photodetectors

In this study, we fabricated deep ultraviolet (DUV) photodetectors based on perovskite thin films doped with halide materials using formamidinium bromide (FABr) and methylammonium iodide (MAI). The device was fabricated using a simple surface engineering technique by post-treating the MAPbI3 perovskite film with an FABr solution. This film acts as a light absorption layer, like a depletion layer with a p-i-n (PIN) structure, with n-type of SnO2-SDBS and p-type of spiro-OMeTAD. Adding 0.10 M MACl to the MAPbI3 precursor solution during the manufacturing process could effectively reduce the trap density compared with existing films. Films with MACl added in the two-step process can control a wide band gap and improve crystallinity. In addition, the Cl atom has a smaller atomic radius than iodine and a higher electronegativity of 3.16, which can improve phase stability, and the effect of the added Cl− increases the electron mobility of the perovskite, showing a fast response.

Incorporation of neodymium, holmium, erbium, and samarium (oxides) in zinc-borotellurite glass: Physical and optical comparative analysis

Investigating the effect of different types of rare-earth oxides on zinc borotellurite glass is important to determine the potential application in optical devices. The addition of rare-earth oxides in zinc borotellurite glass is well-known to enhance the optical properties due to the effects of 4f-4f transitions. In this work, we aim to compare the effect of different rare-earth oxides on zinc borotellurite glass denoted as ZBTNd, ZBTHo, ZBTEr and ZBTSm. The glass samples were successfully fabricated via the melt-quenched technique. The physical investigation of the glasses has been done by measuring the density and molar volume. It was found that ZBTNd glass has the lowest density than the other glasses due to the small atomic radius in neodymium oxide. High-density value for ZBTHo glass shows potential to be used as radiation shielding properties. The high value of molar volume for ZBTNd glass is advantageous for fiber optics as ZBTNd glass has good performance in elasticity. It was found that ZBTEr has a lower refractive index than the other glasses due to low dispersion characteristics. However, ZBTEr glass has good performance to be used in optical communication applications. It was found that the optical absorption shifts to a longer wavelength beginning from ZBTEr > ZBTHo > ZBTNd > ZBTSm. The optical band gap energy for ZBTEr glass is higher than the other glasses due to the Coulomb repulsion energy for erbium which is greater than neodymium and samarium and slightly higher than holmium. The pattern of electronic polarizability for all glasses was found as follows ZBTSm>ZBTNd>ZBTEr>ZBTHo. The optical basicity for ZBTEr was found highest which indicates a higher acidity, meanwhile, the ZBTNd glass has the lowest value which corresponds to a higher basicity.

Tunable optoelectronic performances of fluorinated benzene-EDOT based hybrid electrochromic polymers

Due to its high electronegativity and small atomic radius without undesirable steric hindrance, the incorporation of fluorine atoms into the benzene unit which started from the commercially available compounds is a feasible way to tune the energy levels of polymers, and its electrochromic application is expected to achieve a new breakthrough. Herein, in this paper, benzene units with different fluorine atom numbers were selected as the core and 3,4-ethylenedioxythiophene (EDOT) as the terminal unit, three fluorinated electrochromic precursors (FPh-EDOT, 2FPh-EDOT, and 4FPh-EDOT) were designed and synthesized by Stille coupling reaction, and the corresponding fluorinated π-conjugated electrochromic polymers (P(FPh-EDOT), P(2Ph-EDOT), and P(4FPh-EDOT)) were prepared by electrochemical polymerization method. The effects of different fluorinated benzene units on the photophysics, electrochemistry, and electrochromic properties of precursors and polymers were systematically investigated, and the structure-property relationship was further revealed. All of them have low initial oxidation potentials {FPh-EDOT (0.65 V), 2FPh-EDOT (0.72 V), and 4FPh-EDOT (0.70 V)}, which makes it easy to obtain high-quality new fluorinated polymers at low polymerization potential. With the increase of the number of F atoms, the UV–vis absorption spectra and emission spectra of fluorinated monomer firstly red-shifted and then blue-shifted. The corresponding fluorinated polymers have good electrochemical activity and stability (the P(2Ph-EDOT) activity remained 82.7% after 500 cycles), making it possible to realize their electrochromic devices. All these three fluorinated polymers show obvious color change from the neutral state to the fully oxidized state (P(FPh-EDOT) changes from brown to grayish blue, P(2FPh-EDOT) changes from brown to gray, and P(4FPh-EDOT) changes from dark blue to light blue). The kinetic study further shows that all of them have distinguish electrochromic properties with good optical stability, very short response time (0.9 s for P(2FPh-EDOT) at 700 nm), and favorable coloration efficiency (130.7 cm2 C−1 for P(FPh-EDOT) at 503 nm). Overall, all these three fluorinated polymers have low optical band gap, good redox stability and electrochromic properties, are very promising electrochromic materials, which is worthy for the further research and development.

Effects of vanadium content on the microstructure and tensile properties of NbTiVxZr high-entropy alloys

Vanadium boasts a relatively small atomic radius among numerous refractory alloying elements, yet its effects on the microstructure and mechanical behavior of refractory alloys remain enigmatic. In this work, a series of NbTiVxZr high-entropy alloys (HEAs) with low density were formulated to explore the evolution of microstructures and mechanical properties with varying vanadium content. When the vanadium content was low, the matrix exhibited the single-phase body-centered cubic structure. Excessive vanadium contents (NbTiV0.75Zr, NbTiVZr) disrupted phase stability and tended to aggregate at grain boundaries, forming V-rich and Zr-rich phases. These precipitated phases pinned grain boundaries, impeding grain growth and resulting in both grain boundary strengthening and precipitation strengthening, albeit at the expense of grain boundary cohesion, ultimately leading to brittleness. However, these deleterious phases were redissolved, and fracture elongation increased more than 2 times after water quenching at 1200 °C. The microstructural changes induced by heat treatment were corroborated by alterations in grain boundary relaxation behavior, where the redissolution of precipitated phases after water quenching caused a shift of the grain boundary relaxation internal friction peak to a lower temperature and an increase in peak height. This study elucidates the intrinsic relationship between mechanical properties and microstructures with vanadium content in NbTiVxZr alloys, offering insights for the design of TiV-based lightweight refractory HEAs with high strength and excellent ductility.

Probing hydrogen content in steel using the thermoelectric effect

The issue of hydrogenation of steel is a serious technological problem. Due to its small atomic radius, hydrogen is difficult to analyze quantitatively and qualitatively. Non-destructive estimation of hydrogen content would significantly improve the quality control process. In this work, we attempt to develop a new methodology for the determination of hydrogen content in 4340 steel using the thermoelectric effect. For this purpose, we investigated the mechanisms of hydrogenation, structural and microstructural changes caused by hydrogenation, and performed theoretical calculations of the influence of hydrogen on the electronic structure of steel. Measurements of the Seebeck coefficient were performed using the specially developed μm-resolution scanning thermoelectric microscope (SThM). The KKR-CPA calculations show that hydrogen located at T-voids strongly modifies electronic properties and influences the Seebeck coefficient of the material. Ultraviolet photoelectron spectroscopy (UPS) proves that hydrogenated samples exhibit the valence band onset shift towards higher binding energies concerning the non-hydrogenated materials. Theoretical and experimental studies of the Seebeck coefficient dependence on the total hydrogen content confirm a measurable decrease in the Seebeck coefficient (18.5 µV/K for 0.136 ppm and 13.5 µV/K for 1.03 ppm). Plotted calibration curves for 4340 steel were used for preliminary kinetic studies of the spontaneous dehydrogenation in this material. This work demonstrates that the thermoelectric effect can be used as the basis of a new fast and non-destructive analytical method for the determination of the hydrogen content in 4340 steel.

Thermoelectric properties of heavily Co-doped β-FeSi2

Element doping is a widely employed strategy to enhance the thermoelectric (TE) properties of various materials. β-FeSi2 is a promising low-cost high-temperature TE material with exceptional thermal stability; however, the doping limit of β-FeSi2 is usually very low, which limits the tunability of electrical and thermal properties. Recently, a high doping content of 0.16 in β-FeSi2 has been achieved by the introduction of iridium (Ir), leading to the highest reported figure of merit (zT) of 0.6 in β-FeSi2. Motivated by the successful heavy doping with Ir, this work aims to explore element heavy doping in β-FeSi2 with cobalt (Co), a cheaper, more readily available dopant with a smaller atomic radius and closer electronegativity to iron (Fe). In this study, we successfully obtained a record-high doping content of 0.24 in Co-doped β-FeSi2 through a prolonged annealing process. Despite the absence of a substantial enhancement in the zT of Co-doped β-FeSi2 at high doping levels, with a maximum zT of 0.3 at 900 K in Fe0.92Co0.08Si2, we observed a transition in the carrier transport mechanism as a function of Co doping content, attributed to changes in the band structure. At a low Co doping content (x ≤ 0.12), Fe1–xCoxSi2 demonstrates dominant carrier transport via impurity levels within the band gap, exhibiting hopping conduction. As the Co doping content increases (x > 0.16), the impurity levels overlap and form an impurity band, and the carrier transport turns into the impurity band conduction. The observed band conduction behavior of Fe1–xCoxSi2 (x > 0.16) mirrors that of Ir-doped β-FeSi2, but Fe1–xCoxSi2 shows much lower mobility, which can be attributed to the localized feature of the impurity band introduced by the Co doping. Overall, this study provides insights into the heavy Co doping and its influence on the TE properties and carrier conduction mechanisms in β-FeSi2, helpful for the further development of this TE system.

Effects of polymer precursor conjugation length on the optoelectronic properties of fluorinated benzothiadiazole-based D–A systems

Due to their high electronegativity and small atomic radius without undesirable steric hindrance, the incorporation of fluorine atoms onto a conjugated backbone has been proven to be a very effective way to tune the energy levels of organic semiconductors.

Exploring the influence of cosegregation on mechanical properties of Mg [formula omitted] twin boundaries: A first-principles investigation

This study employs first-principles calculations to investigate the impact of solute segregation on the mechanical properties of the Mg twin boundary (TB). The investigation delves into single-element segregation and multielement cosegregation at the Mg{101¯1} twin boundary. Several parameters, including segregation energy, solubility energy, and strengthening/embrittlement energy, are determined, and Voronoi volume and electronic structure evolution are analyzed. The study discloses the effects of 21 solute single-segregation, as well as the segregation mechanism of Ca, Y, and Zn solute elements in paired combinations. A comparative assessment of the optimal combination for cosegregation of Ca/Y atoms with larger atomic radii and Zn atoms with smaller atomic radii reveals that the solute elements Ca and Y induce more robust energy changes at the interface segregation than Zn. Additionally, electronic structure analysis suggests that charge transfer between solute atoms with large atomic radii and solute atoms with small atomic radii can strengthen the chemical bond at the twin boundary, thereby enhancing the maximum tensile degree, ductility, and formability of the material. The outcomes of this investigation have significant theoretical implications for composition design and the development of novel high-performance multielement magnesium alloys.

The effect of borate on acellular bioactivity of novel mesoporous borosilicate bioactive glasses for tissue engineering

Four novel mesoporous borate-based 13–93 bioactive glass has been synthesized by a modified Stöber method. Thermogravimetric analysis, Inductively coupled plasma atomic emission spectroscopy, Fourier Transform Infrared Spectroscopy, X-Ray diffraction, Brunauer–Emmet–Teller and Barrett–Joyner–Halenda, nuclear magnetic resonance and Scanning Electron Microscope attached with Energy-dispersive X-ray spectroscopy analyses were carried out to investigate the physicochemical properties, in-vitro acellular bioactivity, and the degradation rate of the bioactive glasses in simulated body fluid across a range of times up to 21 days. The characterization data indicates that the bioactive glasses are amorphous and possess mesoporous properties. Likewise, an increase in boron content reduced the surface area and pore volume of the bioactive glass series. The observed decline is attributed to borate units' smaller atomic radius than silicate. The ability to deposit a new apatite layer in the bioactive glasses depends on the borate concentration. As such, an increase in boron content resulted in a decrease in apatite formation. Additionally, the studies showed that bioactive glasses made of borate degraded more quickly than their silicate counterpart. Overall, borate-based 13–93 bioactive glasses were effectively synthesized, and the in-vitro results showed potential usage for these bioactive glasses in tissue engineering situations where it is desirable to control bone growth or delay the onset of bioactivity.

A CuZnMnNiSi alloy interlayer reinforced W alloy/304 stainless steel composite with excellent interfacial strength

Diffusion bonding was successfully applied to join 90 W-7Ni-3Cu (W alloy) with 304 stainless steel (304SS) using CuZnMnNiSi high-entropy alloy (HEA) foil as an interlayer, and the effect of bonding temperature on microstructure and strength of joints was investigated. The present study shows that a sound W alloy/CuZnMnNiSi/304SS joint with sufficient mutual diffusion across the interfaces is obtained at a relatively lower bonding temperature of 900 °C. It is revealed by SEM and HRTEM that the interlayer elements preferentially diffuse into the base materials due to their smaller atomic radius and high activity. At the W alloy/interlayer interface, the Zn and Mn elements in the interlayer diffuse into the (Ni, Cu)ss phase to form (Ni, Cu, Zn, Mn)ss solid solution, while the W phase/interlayer phase forms a semi-coherent bonding. At the interlayer/304SS interface, the Cu and Zn elements in the interlayer diffuse into the 304SS to produce a γ-(Fe, Cu, Zn)ss supersaturated solid solution layer, while the interlayer phase/γ-Fe phase also generate a semi-coherent bonding. In addition, Cu0.64Zn0.36 particles which are judged to be precipitated form the γ-(Fe, Cu, Zn)ss supersaturated solid solution during the cooling process are discovered in the diffusion layer. The joint bonded at 900 °C shows an excellent tensile strength of 403 MPa with good ductility. The tensile fracture occurs at the interface of 304SS/interlayer, showing a mixed fracture mode of intergranular fracture and plastic fracture.

EFFECT OFTHE SUBSTITUTION OF Bi→Sb ON THE STRUCTURE CHANGES WITHIN THE AgBi1-xSbxS2 (x = 0 - 1) SOLID SOLUTION

The work is devoted to study effect of the isovalent substitution on the parameter of structure elements of the crystal structure of the AgBi1-xSbxS2 (x = 0 – 1) solid solution. The limited isostructural phases of the solid solution have a cubic system with space group Fm-3m. The samples of individual composition of the AgBi1-xSbxS2 (x = 0 – 1) solid solution were obtained in quartz vacuumed ampoules in an electric muffle furnace with MP-30 software control of technological processes. The X-ray powder diffractograms that were recorded with using the DRON 4-13 diffractometer have been analyzed using WinCSD software package. The visualization of the crystal structure has been made with VESTA program. It is worth noting that the method of solid phase reactions allows synthesizing sufficiently pure materials, which are suitable for the measure of physical properties. The change of cell parameters within a solid solution is described by a positive deviation from the Vegard’s law. Only all octahedral voids are filled in the structure. It is important to see the prospect of possible alloying by atoms with small atomic radii, which may be localized in tetrahedral voids. The change of volume of the octahedral voids is linear.
 Keywords: crystal structure; solid solution; unit cell.

Study on neutron diffraction and correlated magnetic properties of (R1−xZrx)Fe12−yMoy with low Mo concentration

In order to determine the Zr occupancy site, neutron diffraction study on (R1−xZrx)Fe12−yMoy (R = rare earth) were performed at 300 K and 573 K respectively. It is found that Zr occupies the 2a site, like the R atoms behavior. Zr is the first neighbor of Y in the periodic table, and has a similar chemic property as Y, but with a smaller atomic radius. Due to the suitable chemic property and atomic dimension, the addition of Zr at 2a site facilitates forming of the 1–12 phase, allowing more Fe atoms to enter the 8i site and decreasing Mo content from 1.5 to 0.8. As a result, Sm0.9Zr0.1(Fe0.75Co0.25)11.2Mo0.8 shows a large saturation magnetization σs of 137.6 emu/g, a high Curie temperature TC of 775 K and a strong anisotropy field Ha of 87.5 kOe, and its estimated value of maximum magnetic energy product (BH)max is up to 50.4 MGOe, favorable for permanent magnet applications. At present, almost rare-earth sintered magnets are made of Nd2Fe14B, causing the price of the raw material Nd to soar. Therefore, the development of low-cost Sm-Fe based hard magnetic materials is of particular significance.

Microstructure and properties of Al0.5NbTi3VxZr2 refractory high entropy alloys combined with high strength and ductility

Novel lightweight Al0.5NbTi3VxZr2 (x = 0.5, 1.0, 1.5) refractory high entropy alloys were synthesized by vacuum arc melting. The microstructure evolution and mechanical properties of Al0.5NbTi3VxZr2 alloys were analyzed. All Al0.5NbTi3VxZr2 alloys have a single BCC structure, and the addition of V does not change the microstructure of the alloys. At elevated temperatures, V1.0 alloy shows good phase stability, and the compressive yield strength of V1.0 alloy is 898 MPa at room temperature, 706 MPa at 873 K, and 110 MPa at 1073 K, respectively. Al0.5NbTi3VxZr2 alloys reveal excellent compression deformability, all samples can be compressed to more than 50% strain at room and elevated temperatures without fracture. At room temperature, V1.0 alloy still possesses the best tensile properties, with the yield strength of 694 MPa. The enhancement strength is due to the addition of V element with small atomic radius, which is caused by a variety of strengthening mechanisms, including solid solution strengthening and grain refinement strengthening. Most of the reported Al–Nb–Ti–V–Zr system refractory high entropy alloys have poor deformability at room temperature, and most of the work is focused on their compression properties. The Al0.5NbTi3VxZr2 refractory high entropy alloys prepared in the present work not only have excellent compression deformability, but also excellent tensile properties. Our present study not only promotes the development of toughening Al–Nb–Ti–V–Zr system refractory high entropy alloys to challenge engineering applications, but also provides guidance for the design of lightweight high temperature materials with a variety of strengthening mechanisms.

Effect of Group-10 Element M (Ni, Pd, Pt) on Electronic Structure of Icosahedral M@Au12 Cores of MAu24L18 (L = Alkynyl, Thiolate)

Heterometal doping into chemically modified gold clusters is a straightforward method to modulate their electronic structure. Although examples exist of alloy clusters containing a series of heterometeal dopants from different groups of the periodic table, it is rare for a complete set of alloy clusters to contain dopants from the same group. In this work, we newly synthesize Ni-doped gold clusters with NiAu24L18 [L = ArFC≡C– (ArF = 3,5-(CF3)2C6H3), PhC2H4S–] by using hydrogen-containing phosphine-protected NiAu clusters as precursors. The synthesis of the Ni-doped counterpart allows us to compare the geometric and electronic structures of prototypical alloy clusters with a M@Au12 core (M = Ni, Pd, Pt). Single-crystal X-ray diffraction analysis indicates that due to the small atomic radius of Ni, NiAu24L18 has a slightly contracted core than clusters with M = Pd or Pt. Voltammetry and optical absorption spectroscopy suggest that the modified jellium model cannot solely explain the period-dependent doping effect because the Ni@Au12 core contracts. MAu24L18 clusters (L = PhC2H4S–) are paramagnetized by single electron reduction, and their magnetic properties are investigated by using electron spin resonance spectroscopy. This work thus provides a guide for designing gold clusters by heterometal doping within a given group of the periodic table.

Research on a fluorine-containing asphaltene dispersant and its application in improving the fluidity of heavy oil

The high viscosity characteristics of heavy oil make it difficult to extract, transport and process. Therefore, enhancing the fluidity of heavy oil can effectively improve the economic benefits of heavy oil resource development. Aggregation and precipitation of asphaltenes are the main causes of high viscosity of heavy oil. Asphaltene molecules are able to self-associate by intermolecular forces such as hydrogen bonding and π-π interactions, resulting in the formation of supramolecular aggregates with large particle size, leading to the increasing of viscosity of heavy oil. Fluorine is the most electronegative element and has a strong ability to form hydrogen bonds. This is due to the special role of the element fluorine, including high electronegativity and small atomic radius. In this study, the fluorine-containing copolymer was synthesized and used to disperse asphaltenes. This copolymer was also used for viscosity reduction on heavy oil in a block in Xinjiang, and the viscosity reduction rate (VRR) reached 70.25% at 600 ppm. Possible mechanism of asphaltene dispersion was proposed by fluorescence microscopy, X-ray diffractometry (XRD), scanning electron microscope (SEM), atomic force microscope (AFM) and transmission electron microscopy (TEM). The mechanism of interaction between copolymer and asphaltene by hydrogen bonds was further analyzed by infrared spectroscopy.