查看更多>>摘要：Mg-25Sn (wt%) mixtures were prepared by mechanical alloying (MA), and then cold-compacted into preforms. Correlation of milling time with phase evolution during MA and their thermal stability in the subsequent heating-up process was investigated. The raw nano-sized Sn powder is conductive to the accelerated synthesis of Mg2Sn phase, by which nano cubic and hexagonal Mg2Sn could be obtained after 5 h and 20 h MA, respectively. During the heating process, the residual Sn in the short-time ball milling (5 h, 10 h) transforms mainly into Mg2Sn bulk through melting and subsequent diffusion reactions. However, the 20 h MAed mixture has experienced inverse eutectic and subsequent thixotropic reactions, in which metastable-to-equilibrium transition of Mg2Sn occurs. Mg2Sn phase formed in the two cases are nanosized. A uniform dispersion of fine Mg2Sn phase and the retention of inverse eutectic liquid phase primarily account for the improvement in mechanical properties of the sintered material.
查看更多>>摘要：Topologically close-packed (TCP) phases such as μ and Laves phases formed during solidification has an important influence on the mechanical properties of superalloys. Understanding the formation and elimination mechanism of TCP phases is the key to promote the development of superalloys. In this study, C15-Laves phase was first found in a Hf-containing Co-based superalloy, meanwhile, the formation mechanism and thermal stability of the C15-Laves phase were clarified. The results showed that the formation of C15-Laves phase was associated with the segregation behavior of alloying elements during solidification: Co, W and Cr segregated to the dendrite core, and Hf, Ta, Ti, Mo, Ni, Al, Si segregated to the interdendritic region. In the final stage of solidification, the C15-Laves phase enriched in Hf, Ta and Ti formed, and it had similar lattice parameters to the C15-Co2Hf phase. The incipient melting point of C15-Laves phase was between 1170 ℃ and 1180 ℃, and it gradually decomposed to form the Hf-rich MC carbide during solution treatment. The large formation energy differences between the MC carbide and C15-Laves phase promoted a rapid elimination of the C15-Laves phase, which reduced solution treatment time of the alloy. The results can provide a theoretical basis and experimental data support for the composition design and heat treatment process optimization of multicomponent novel Co-based superalloys.
查看更多>>摘要：Magnetic, pseudogap, topological, magnetostructural, and elastic behaviors of Mn3Sb have been unraveled. The ferrimagnetism (FIM) is described by localized and delocalized electron magnetism resulting in different magnetic moments on Mn atoms, confirming the neutron diffraction data. The identified magnetostructural properties are due to the non-equivalent Mn atoms in its lowest symmetry structure. The electronic structure is also unique due to variable valance states of Mn atoms. The magnetic moment (4.10 μB) of non-equivalent Mn1 atom is antiparallely aligned with the magnetic moments (2.34 μB) of Mn2 and Mn3 atoms. The estimated Curie temperature, TC, is higher than the room temperature, which may have above the room temperature applications in spintronic devices. The band structure and density of states (DOS) show the characteristics of band topology (opening of a gap in Dirac-like band features) and pseudo-gap, respectively, around the Fermi level. While expanding the unit cell, the tetragonal FIM ground state transforms to the cubic primitive FIM phase, however, the contraction transforms it to the L12 ferromagnetic (FM) phase. The estimated elastic constants, bulk to shear modulus ratio, and elastic anisotropy factor indicate that Mn3Sb exhibits mechanically stable, ductile, and anisotropic behaviors, respectively.
查看更多>>摘要：High-temperature ferromagnetism in materials composed of non-magnetic constituents is one of the most intriguing aspects in condensed matter physics as well as materials science. Beyond oxide compounds where the ferromagnetism is mainly induced by dilute magnetic dopants, a variety of unusual ferromagnetic materials, mostly fabricated artificially to control the magnetic and electronic properties, have been investigated for spintronic device applications. The unexpected ferromagnetism, attributed to strain and structural defects or proximity and interfacial effects, is now extended to quantum materials, despite prevailing controversy on its physical origin. Recently, the ferromagnetism observed in topological materials with high mobility arising from the linear energy dispersion invokes new interest in the field of spintronics. Here, we report experimental verification of peculiar high-temperature ferromagnetism in β-Ag2Se topological semimetal, composed of non-magnetic constituents. We have fabricated stoichiometric Ag2Se (S-Ag2Se) and Ag-vacant Ag2Se (V-Ag2Se) samples. Contrary to non-magnetic behavior of S-Ag2Se, V-Ag2Se shows distinct ferromagnetic response up to room temperatures. First-principles calculations demonstrate that the ferromagnetic ordering occurs only in V-Ag2Se if there is finite Hubbard U, which can be explained by self-trapped magnetic polaron model with strong p-d hybridization. High-temperature ferromagnetism, especially in topological materials, allows exploring a significant new direction in material engineering for spintronic applications.
查看更多>>摘要：Photocatalytic water splitting under irradiation by sunlight to achieve hydrogen with the participation of semiconductor materials is deemed as the most promising green and clean energy supply strategy. Hence, it is particularly important and emergency to design photocatalyst with both high activity and stability to perform high-efficiency hydrogen evolution reaction (HER). In this study, we report a competitive coordination strategy to modulate the electron and band structure of g-C3N4 dramatically improving the HER kinetics. Experimental and density functional theory (DFT) calculations results inferred that the modified g-C3N4 by copolymerizing urea and diaminodiphenyl sulfone can promote the effective separation of photogenerated electrons and holes, and simultaneously significantly increase the fluorescence lifetime of g-C3N4. Specifically, the hydrogen generation rate is 3.7 or 9.6 folds higher of the original carbon nitride at λ > 400 nm and λ > 420 nm, respectively. Additionally, the optimal catalyst exhibits a high apparent quantum yield (7.02%) when the incident wavelength is 420 nm as well as excellent stability. This work will shed a spick-and-span insight for conception and preparation of high-powered metal-free photocatalysts.
查看更多>>摘要：In this work, the effect of Ti content on the microstructure and mechanical properties of low-density Fe-30Mn-10Al-1.57C-2.3Cr-0.3Si-χTi (χ = 0, 0.3, 0.6, and 0.9 wt%) alloys was systematically investigated. The results reveal that hot deformation, followed by solid-solution treatment at 1050 °C (3 h) and thermal aging at 350 °C (6 h), ensures outstanding mechanical properties. The low-density alloys exhibit completely austenite microstructures with carbides. The original carbide phase, the so-called κ-carbide, is observed in the low-density Ti-free specimen. However, increase in the Ti content leads to the reduction of this phase and the emergence of a new type of carbide, i.e., TiC. Moreover, the grain size of austenite phase is refined with Ti addition, resulting in a superior yield strength. In addition, the low-density alloy with a Ti concentration of 0.6 wt% demonstrates optimal mechanical properties with the yield strength of 1031.75 MPa, the ultimate tensile strength of 1158.55 MPa, and the total elongation of 23.96%. It is worth noting that the novel low-density alloy exhibits a density of 6.65 g/cm3, which is ~14.74% lower than that of traditional steel (7.8 g/cm3) and can be ascribed to the incorporation of lightweight Al element.
查看更多>>摘要：The Au-Cu nanoalloys (NPs) were produced by NaBH4 co-reduction from the mixture precursor solution of component Au and Cu, under the protection of sodium citrate stabilizer. The Au-Cu NPs encapsulated in SiO2, Au5Cu5@SiO2 NPs, were then synthesized by the St?ber method based on the obtained Au-Cu NPs. The microstructure and particle sizes were characterized by TEM observation. The phase transition temperature of Au-Cu@SiO2 was determined by DSC measurement. The surface tension, surface segregation and surface energy of Au-Cu NPs as a function of particle size and temperature were calculated by the theoretical model based on the thermodynamic properties of pure component of Au and Cu NPs, respectively. The thermodynamic parameters of Au-Cu system at various nanoscales were optimized on the basis of experimental and theoretical results in this work and previous results in literature. Based on the obtained the thermodynamic data set, the nano phase diagrams of the Au-Cu system at nanoscale were calculated, and the thermodynamic properties of Au-Cu nanometer system were obtained. The results show that the calculated results agree well with experimental work.
查看更多>>摘要：Sb2O5 is considered as a high capacity promising anode for LIBs and SIBs due to its high theoretical capacity of 1324 mAh·g?1. However, the large volume expansion during the cycling process makes the SEI film on its surface continuously reorganize and even break, which limits its electrochemical performance. In this work, we construct an anode consisting of Sb2O5 nanoparticles grown on carbon cloth with coating SiO2 (denoted as SiO2/Sb2O5/CC) to improve the structure of SEI film, which realizes stable SEI film and brings high energy storage performance. When SiO2/Sb2O5/CC composites are used as anode material for LIBs and SIBs, they both have high specific capacity and stable cycle performance (909.5 mAh·g?1 at 1 A·g?1 after 500 cycles) in LIBs and (630.7 mAh·g?1 at 200 mA·g?1 after 150 cycles) in SIBs. That is attributed to the SiO2 has a positive synergistic effect on the structure and electrochemical properties of Sb2O5 materials. Specifically, the existence of SiO2 slows down the repeated fracture and recombination of SEI film caused by the volume effect of Sb2O5. So the reversibility of electron and ion transport is better, and the capacity retention is better. Consequently, this wok can provide new insight for exploration and design of Sb2O5 anode materials for LIBs and SIBs.
查看更多>>摘要：Electronic structure is known to be highly influenced by the site occupancy and the stoichiometry of the material which in turn largely effects the thermoelectric properties. Herein, we present electronic calculations using density functional theory (DFT) of non-stoichiometric Ti doped NbFeSb configuration, showing the effect of the anti-site Fe atoms on the electronic properties, and supporting them with experimental results of the prepared Nb0.8Ti0.2Fe1+xSb1?x samples. The electronic structure of the non-stoichiometric sample shows the introduction of two distinct peaks near the Fermi level by the Fe atoms at the Sb sites. These resonance states are known to cause an increase in the density of states effective mass near the Fermi level, which explains the increase in the Seebeck coefficient in the sample x = 0.03 compared to the sample x = 0.00. In addition, a comparatively higher electrical conductivity is reported from sample x = 0.03, which is attributed to the aliovalent substitution of Sb atoms by Fe atoms. The simultaneous increase in the Seebeck coefficient and electrical conductivity culminates in an increased power factor of ～50.3 μW/cmK2 at 373 K, which is ～46% higher than that of samples x = 0.00 and x = 0.05, highlighting the possibility of increasing the power density by stoichiometric variation to achieve the high joule-per-dollar performance of NbFeSb-based TE devices, the relevance of which is also currently emphasized in the quest for commercial viability.
查看更多>>摘要：In dye-sensitized solar cells (DSSCs), TiO2 has long been a popular electron transport material for carrying photo-generated electrons from the dye to the outer circuit. However, increasing the electrical conductivity of TiO2 while preserving its properties is one of the most significant challenges for increasing DSSC efficiency. Here, cobalt-reduced graphene oxide co-doped TiO2 nanoparticles were synthesized by a modified sol-gel procfess that together controlled the particle size as well as narrowed bandgap of nanoparticles as determined by XRD and UV-Vis absorption measurements. The SEM and TEM were used to perform in-depth morphological characterization of the newly synthesized nanocomposites while J-V (current-voltage) curves, EIS Nyquist curves, and incident photon to current conversion efficiency (IPCE) spectra were used to examine the photovoltaic parameters. Enhanced short circuit current density (Jsc 12.83 mA cm?2), open-circuit voltage (Voc 0.618 V) and overall power conversion efficiency (PCE, η = 5.24%) of DSSC was obtained with Co/rGO co-doped TiO2 based photoanode in comparison to bare TiO2 (η = 3.71%), cobalt doped TiO2 (η = 4.09%) and rGO doped TiO2 (η = 4.43%) based DSSCs. Huge improvement in efficiency, 41% higher PEC in Co/rGO co-doped TiO2, was attributed to better utilization of visible radiations, greater dye adsorption and enhancement in charge transfer properties by suppressing the electron transport resistances. The incorporation of rGO improved electron transfer, which compensated for recombination losses, thereby increasing the DSSC's Jsc. The synergetic role of rGO and transition metal helped in keeping the structure intact in the nano-assembly that enhance the photo-generated carriers.
NSTL
Elsevier