查看更多>>摘要：For the first time, the interaction of magnetic materials R2Fe17 (R = Nd, Sm, Ho) with hydrogen at 200 and 250 °C and a hydrogen pressure of up to 50 atm was studied by Calvet calorimetry. The dependences P = f(C), ΔHabs.(des.) = f(C) and ΔSabs. = f(C) were obtained (P is the equilibrium pressure of hydrogen, ΔH is the enthalpy of the reaction, ΔS is the entropy of the reaction, C = H/ IMC). It was found that the values of the enthalpy of the reaction of hydrogen with IMC (intermetallic compound) change with changes in the temperature of the process, the concentration of hydrogen in the metal matrix, as well as during the transition from one compound to another. On the plots of the dependence ΔHabs. (des.) = f (C) two sections can be distinguished where the enthalpy values are constant. It is suggested that the observed changes in the thermodynamic parameters of the process are related to the order of filling the interstitial sites 9e and 18g. The process of filling 9e interstitial sites occurs in two stages with different enthalpy (entropy) of the reactions.
查看更多>>摘要：The glass forming ability (GFA) is a problem of great concern in the research of amorphous materials. It is of great significance to understand the physical mechanism of GFA and to seek conditions and methods to improve it. In this study, we collected 820 experimental data from existing literature, and used gradient boosted decision trees (GBDT) model to predict the GFA. The GBDT model optimized by 10-fold cross-validation and grid search technology shows excellent predictive results. The determination coefficient (R2) and root mean square error (RMSE) are 0.652 and 2.85, respectively. Compared with the previously reported 27 criteria and ML models, GBDT model has the highest prediction ability. The result exhibit that the predictive performance of GBDT can be significantly improved by considering the atomic size difference, total electronegativity, mixing entropy and average atomic volume.
查看更多>>摘要：Single crystals of six new non-stoichiometric quaternary chalcogenides with a general formula Ba2?δLn1?xMn2?yQ5 (Ln = Pr, Nd, and Gd; Q = S and Se) have been synthesized by the molten flux method. Single crystal X-ray diffraction (SCXRD) studies show that these compounds are isostructural and crystallize in the monoclinic space group C2/m with two formula units. These structures show occupational disorder at the metal sites, and the SCXRD refined compositions of these compounds are Ba2Pr0.88(1)Mn1.79(1)S5, Ba2Nd0.83(1)Mn1.89(1)S5, Ba2Gd0.82(1)Mn1.77(1)S5, Ba1.86(1)Pr0.61(1)Mn1.88(1)Se5, Ba1.90(1)Nd0.57(1)Mn1.93(1)Se5, and Ba1.88(1)Gd0.56(1)Mn1.95(1)Se5. The sulfide structures have split positions for Mn atoms with the concomitant occupational disorder at the Pr and Mn sites. In contrast, the selenide structures do not exhibit split Mn sites. The Ba sites in these selenides also show occupational disorder along with partially occupied Ln and Mn sites. The crystal structures of the selenides are comprised of [2∞Ln1?xMn2?ySe5]n? layers separated by Ba2+ cations. The Ln atoms in these sulfides and selenides are octahedrally coordinated with six Q atoms, and each Mn atom is bonded with four Q atoms forming a distorted tetrahedral geometry. The charge balancing in these structures is difficult due to the metal vacancies. The optical absorption study on the polycrystalline Ba1.88Gd0.56Mn1.95Se5 sample reveals a direct bandgap of 1.73(2) eV in agreement with the reddish color of the sample. The density functional calculations are performed to study the atomic and electronic structures of Ba1.88(1)Gd0.56(1)Mn1.95(1)Se5.
查看更多>>摘要：The low sulfur utilization and the serious shuttle effect of polysulfides severely hamper practical application of Li-S batteries. Herein, sulfur cathodes with the multi-functional structures, featured with double-layered hollow carbon sphere with up to 50 nm interlayer space (DLHC-50) in situ grown Co-SnS catalytic layer is designed and synthesized for lithium sulfur batteries. Co-SnS/DLHC-50 can encapsulate 72% sulfur, higher than 63% for Co-SnS/DLHC-20 due to the large interlayer spaces of DLHC-50. Meanwhile, polysulfides are also effectively restricted via physical entrapment from DLHC-50 as well as chemical binding between Co-SnS and polysulfides. Benefiting from the well-constructed host framework, Co-SnS/DLHC-50 @S shows higher specific capacity/capacity retention of 760.4 mA h g?1/72.9% after 500 cycles at 0.5 C, than that of 546.5 mA h g?1/62.2% and 668.9 mA h g?1/62.2%, for DLHC-50 @S, and Co-SnS/DLHC-20 @S, respectively. In addition, the strategy can be also extended to prepare other metal oxides (sulfides)/DLHC-50 for wide applications. Therefore, this work demonstrates a promising route to combat some bottlenecks such as low sulfur utilization, and the shuttle effect of polysulfides for Li-S batteries.
查看更多>>摘要：Achieving semi-insulating (SI) GaN epilayers with low threading dislocation density (TDD) on sapphire substrates is critically important but challenging for electronic and optoelectronic devices. To obtain low-TDD SI GaN within a thin layer, herein, we performed interfacial engineering for early regulating dislocation and impurity behaviors. It is found that introducing an ultrathin (10 nm) sputtered AlN interfacial buffer layer can effectively suppress dislocations and oxygen (O) impurities. Compared with GaN and thick AlN buffer layers, the ultrathin AlN buffer layer can be nano-pixelated into discrete islands with higher density, ensuring an adequate three-dimensional growth with locally quick coalescence. Hence, the TDD value of the GaN epilayer was rapidly decreased to a low level at the earlier stage of growth. In addition, benefiting from the high diffusion barrier of O in AlN, AlN buffers demonstrate a superior blocking effect of O impurities over GaN buffer, even if the thickness is only 10 nm. Finally, GaN epilayer with a TDD value of 2.7 × 108 cm?2 and a sheet resistance of 2.43 × 1011 Ω/sq can be achieved at the same time. The interfacial buffer engineering provides a simple and effective strategy to obtain high-crystalline-quality SI materials, without additional negative effects introduced.
查看更多>>摘要：We report the evolution of microstructure and hardness homogeneity in arc melted ingots (AMIs) and suction cast rods (SCRs) of CoCrFeNiNbx (0.45 ≤ x ≤ 0.65) eutectic high entropy alloys (EHEAs) solidified at cooling rates of ~10–103 K/s. The effect of cooling rate on the evolution of phase and microstructure, has been investigated thoroughly by using scanning electron microscopy, x-ray diffraction. Whereas the mechanical properties have been investigated by compression test and Vickers microhardness. The microstructure of the EHEAs comprised of FCC and Fe2Nb type Laves phase, which remained the same under different processing conditions. The AMIs exhibited a high yield strength of 1.4–2.0 GPa with high compressive fracture strain up to 17.4% at room temperature. The SCRs showed improved yield strength of 1.5–2.3 GPa, due to the higher cooling rate and nano-/ultrafine lamellae thickness (λw). The λw values and hardness vary between 130 and 220 nm and 581–620 HV, respectively, in fully eutectic x = 0.5 AMI pointing to the evolution of a homogeneous microstructure and homogeneous distribution of the alloying elements in the phases. The hardness in 3 mm? SCRs is 10% higher than that of AMI due to similar microstructure homogeneity and refinement of λw. The proeutectic FCC shows low Nb solubility with a partitioning coefficient of kNb <<1, and Laves phase with kNb>>1 shows higher Nb solubility and preferential dissolution due to the high melting temperature, large atomic radii and large negative enthalpy with other constituent elements.
查看更多>>摘要：FeRh films exhibit an extraordinary magnetic phase transition accompanied by structural and electrical variations. This study intentionally modified the local atomic environment using hydrogen irradiation to elucidate the transition characteristics. It was observed that with the increase in hydrogen irradiation, the initial residual-ferromagnetic state in the antiferromagnetic region (i.e., below the magnetic phase transition temperature) increased. In addition, the transition temperature decreased. Structural and chemical analysis revealed that the increased hydrogen irradiation enhanced local structural distortion and Fe-Frenkel defect formation. Furthermore, density functional theory calculations confirmed that the Fe-Frenkel defect affected the breakdown of hybridization between Fe and Rh. Therefore, it caused the increased residual ferromagnetic state below the transition temperature and decreased the transition temperature.
查看更多>>摘要：Aluminum matrix composites with in situ core-shell structure were successfully prepared by powder metallurgy. And the microstructure, mechanical properties and tribological behavior of core-shell structure reinforced aluminum matrix composites were investigated in detail. The results indicate that double core-shells of Al3Ni and NiAl are formed between the Al matrix and Ni3Al reinforcements. The combined effect of Ni3Al reinforcements and the in situ core-shell structure enhance the mechanical and tribological properties of the composites, which is due to the improved strength of the composites and bonding strength between the reinforcements and matrix. Moreover, the serious adhesive wear is significantly alleviated for the composites. Overall, the N15 composite reinforced with 15 vol% Ni3Al exhibits good comprehensive properties, which shows the highest compressive strength of 248 MPa with a strain of 10%, and the optimal friction coefficient and wear rate of 0.74 and 6.45 × 10?5 mm3/(N m), respectively.
查看更多>>摘要：2D MXenes have been brought into sharp focus in electrochemical energy-storage devices due to their excellent electronic conductivity, high specific surface area, tunable layer structure, and large redox-active surface areas. Nevertheless, further applications of MXenes as electrode materials for supercapacitors are severely limited by the low theoretical specific capacity and self-restacking. Herein, a Ti3C2TX @NiO heterostructure is constructed firstly by uniformly deposition of NiO nanosheets on Ti3C2TX substrate, then the composite is incorporated into 3D porous hydrogel via an efficient graphene oxide (GO)-assisted self-convergence hydrothermal strategy with low temperatures. Owing to the synergistic effect among each components and the 3D porous interconnected architecture, the resultant 3D hierarchical Ti3C2TX @NiO-Reduced Graphene Oxide (RGO) heterostructure hydrogel not only takes both merits of highly conductive and outstanding pseudocapacitive, but also significantly prevents the aggregation and increases the surface utilization of Ti3C2TX @NiO. The 3D hierarchical Ti3C2TX @NiO-RGO heterostructure hydrogel electrodes (without binders) exhibit an enhanced electrochemical performance, with a superb specific capacitance up to 966 F g?1 at 1 A g?1 and long-term stability of 94.5% over 10,000 cycles. Importantly, a maximum energy density of 58.5 Wh kg?1 is obtained at power density of 550 W kg?1. Our work provides a facile and efficient approach to develop Ti3C2TX-based heterostructure hydrogels with improved overall performance, which expands the practical applications of MXenes in supercapacitors.
查看更多>>摘要：Nb-based dual-phase alloys are one of the most promising candidates for hydrogen purification. To solve their brittle fracture in hydrogen-containing atmospheres, the ductile-to-brittle transition-hydrogen concentration (DBTC) is a significant reference index, and the dissolved hydrogen concentration should be controlled below the lower limit of the DBTC, i.e., 0.72 H/M (atomic hydrogen to metal ratio). In this study, hydrogen permeable Nb-Ti-Fe alloys were designed and developed by using the above DBTC concept. Four hyper-eutectic Nb-Ti-Fe alloy membranes were prepared, and their hydrogen solubility was systematically analyzed by corresponding pressure-composition isotherms (PCT curves). The results show that all these samples had a linear relationship between the hydrogen concentration and square root of the hydrogen pressure between 0.1 and 0.4 MPa, which is in accordance with the Sieverts’ law. The hydrogen solubility of the specimens containing the primary TiFe phase was lower than 0.72 H/M, but the alloys with the primary Nb phase had a value that was much higher. The latter was completely broken during the test, even if the feed hydrogen pressure was reduced to 0.15 MPa. Based on the above results and DBTC concept, novel insights into the design of Nb-Ti-Fe hydrogen permeable alloys were elucidated; that is, an improvement in both the hydrogen permeability and hydrogen embrittlement resistance can be attained by controlling the hydrogen solubility. Following this concept, a Nb5Ti58Fe35Cu2 alloy was successfully developed that exhibited a high permeability of 4.32 × 10?8 mol H2 m?1 s?1 Pa?0.5 at 673 K, which is 2.7 times than that of a pure Pd membrane under the same test conditions. The present work demonstrated the feasibility and applicability of the DBTC concept in the design of dual-phase Nb-Ti-Fe hydrogen permeable alloy membranes.
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Elsevier