查看更多>>摘要：In this study, the solidification and precipitation process of Ni75Al18Cr7 superalloy was investigated based on the microscopic phase-field method. The simulation results were validated by using the experimental results. There were three types of ordered interfaces between L1(2) phase, namely (200)(L)//(200)(L).1/2[001](L),(200)(L)//( 200)(L) and (100)(L)//(200)(L).1/2[001](L), which were studied by plotting the microstructural characteristics of Ni75Al18Cr7 superalloy and the distribution of atomic occupation probability and evolution of atomic occupation probability on both sides of the interface between L1(2) phases. The simulation results show that the former two interfaces could migrate with the precipitation evolution process, while the latter ordered interface (100)(L)//(200)(L).1/2[001](L) could not migrate. The interface migration was caused by the migration and exchange of Ni/A1 atoms at the ordered interface. The atomic concentration in the ordered interface before and after migration was almost constant, i.e., the segregation and dilution of each atom was almost constant. The experimental results show that the L1(2) phase structure grew gradually with the increase in heat treatment time, which is consistent with the simulation results of microscopic phase-field method. Moreover, the volume fraction of L1(2) phase calculated by the phase-field method was almost the same as that obtained by X-ray diffraction (XRD) experiments, which indicates the feasibility of using microscopic phase-field method to guide the optimization design of alloy. (C) 2021 Elsevier B.V. All rights reserved.
Sharma, VaibhavNaphy, JaredBishop, OmarBennett, Steven P....
7页
查看更多>>摘要：The effects of post-synthesis annealing temperature on arc-melted samples of Fe3Ga4 has been studied to investigate changes in crystallographic and magnetic properties induced by annealing. Results show a significant trend in the evolution of the (incommensurate spin density wave) ISDW-FM (ferromagnetic) transition temperature as a function of the refined unit cell volume in annealed samples. Strikingly, this trend allowed for the tuning of the transition temperature down to room-temperature (300 K) whilst maintaining a sharp transition in temperature, opening the door to the use of Fe3Ga4 in functional devices. Crystallographic analysis through Rietveld refinement of high-resolution x-ray diffraction data has showed that arc-melted stoichiometric Fe3Ga4 is multi-phase regardless of annealing temperature with a minor phase of FeGa3 decreasing in phase fraction at higher annealing temperature. In order to validate the trend in ISDW-FM transition temperature with regard to unit cell volume, high pressure magnetometry was performed. This showed that the FM-ISDW 68 K) and ISDW-FM 360 K) transition temperatures could be tuned, increased and decreased respectively, linearly with external pressure. Thus, external pressure and the ensuing crystallographic changes minimize the temperature range of the stability of the ISDW pointing toward the importance of structural properties on the mechanism for the formation of the intermediate ISDW phase. These results show how this model system can be tuned as well as highlighting the need for future high-pressure crystallography and related single crystal measurements to understand the mechanism and nature of the intermediate ISDW phase to be exploited in future devices. Published by Elsevier B.V.
Bhoriya, AnkitRaghav, D. S.Bura, NehaYadav, Deepa...
11页
查看更多>>摘要：The manuscript reports temperature-dependent magnetic transitions correlated to variations in the phonon modes in Nd1-xSrxMnO3. Synthesis of x = 0.4 & 0.5 compounds by the solid-state reaction method was followed by structural/microstructural and electronic characterizations. The crystal structure of both compositions is orthorhombic with Pbnm symmetry, as confirmed by x-ray diffraction. The XPS data con-firm the mixed Mn valance with the desired stoichiometry. The phase-separated nature is manifested through the occurrence of various phases, e.g., spin-glass (SG), charge order (CO), ferromagnetic (FM), and paramagnetic (PM), as the temperature is varied from 20 to 300 K. The temperature-dependent Raman measurements reveal that although the material is structurally stable in the studied temperature range of 80-440 K, noticeable discontinuities in the phonon mode shifts were noticed. These phonon mode shifts are found to directly correspond to the magnetic transitions. The change in the frequency of the Raman modes with temperature, which causes the observed shift, could be attributed to various factors such as lattice expansion, anharmonic interactions, spin-phonon coupling, electron-phonon interaction, etc. Here, we have used spin-phonon coupling along with lattice expansion as well as anharmonic interactions to describe the behavior of modes in the FM regime and lattice expansion and anharmonic interaction in the PM phase. (C) 2021 Published by Elsevier B.V.
查看更多>>摘要：The high-pressure and high-temperature (HPHT) technique was employed to prepare skutterudite-based polycrystalline materials Co4Sb11TexSn1-x (x = 0.5, 0.6, 0.7). The thermoelectric properties, as well as electrical transport properties near room temperature, were researched systematically. The results indicated that the Sn and Te co-doped specimens yielded an impressive depression in lattice thermal conductivity (kappa(L)) based on the point-defect scattering. The kappa(L) exhibited a positive Te doping level dependence. Therefore, a minimum lattice thermal conductivity was 1.41 Wm(-1)K(-1) for Co4Sb11Te0.7Sn0.3. Consequently, the thermoelectric dimensionless figure of merit, ZT, was remarkably enhanced from 300 to 725 K. The maximum ZT was 1.13 for Co4Sb11Te0.7Sn0.3 at 711 K, which is better than that of pure Co4Sb12. This value is nearly improved one order of magnitude and rivals the state-of-the-art single-filled n-type skutterudite compounds. Compared to the traditional synthesized method, high pressure and high-temperature techniques can fundamentally reduce the reaction duration from several days to less than an hour and provide a different route for the synthesis of thermoelectric materials. (C) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：Auxetic structure is a typical metamaterial, whose mechanical behaviors of two-dimensional and threedimensional structures are widely studied. However, reports on surface auxetic structure (SAS) are rare. As a consequence, two types of SAS were designed by reversing and crimping the concave hexagonal plane auxetic structure (PAS) composed of double arrows, which were known as RAS and CAS, respectively. The theoretical equations to calculate the deformation of the representative volume cell structure (RVCS) were derived, and the relationships between energy and work were established based on the plastic wrinkle. The compressive simulations of the plane and surface auxetic structures were conducted through the use of finite element method (FEM) verified by experiment, and the mechanical behaviors and energy absorption characteristics were obtained. By comparing the simulation results of different structures, it was found that RAS not only realized the auxetic effect of compression shrinkage but also realized the supermechanical effect of compression twist. The auxetic effects of these structures were realized by the deformation of beams. The auxetic effect only appeared in the local positions of these structures, and other positions still belonged to the positive Poisson's ratio effect. The crimped CAS had the biggest maximum load peak, and PAS possessed the highest specific energy absorption (SEA). The supermechanical effects of compression shrinkage and compression twist in RAS have great potential in some distinctive engineering applications. (c) 2021 Elsevier B.V. All rights reserved.
Montahaei, RezaEbrahimi, S. A. SeyyedYourdkhani, AminPoursalehi, Reza...
10页
查看更多>>摘要：In this study, thin films of undoped and Nb-doped hematite were grown on FTO-coated glass substrates via the liquid-phase deposition method as photoanodes for PEC water splitting applications. The samples were then annealed and flame-treated for 90 s with a butane flame. At all doping concentrations, the thinnest films (similar to 200 nm) yielded the best properties. FESEM images showed that film morphology is not dependent on Nb-doping concentration. Compared with the undoped hematite film, the optimum Nb-doped sample showed an approximately five-fold increase in photocurrent density at 1.6 V vs. RHE and a similar to 0.3 eV decrease in energy band gap value. The charge carrier density value of the optimum Nb-doped sample was shown to increase from 1.38 x 10(17) to 3.54 x 10(18) cm(-3) after flame treatment due to the introduction of oxygen vacancies. The number of times the reducing butane flame is applied was shown to affect the PEC performance, both positively and negatively, giving rise to an approximately sixteen-fold increase in photocurrent density at 1.6 V vs. RHE in comparison with the untreated sample after four times of application. Butane flame treatment was also shown to facilitate the process of charge transfer in Nb-doped hematite and its interface with the electrolyte. (C) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：The properties of MAX phases can be fine-tuned to meet some particular applications via solid solution route, and the feasible preparation of the MAX solid solutions is a prerequisite for their applications. Ti3(SnxAl1-x)C2 solid solutions over the whole composition range (x = 0-1) are synthesized by pressureless sintering, and characterized by XRD and SEM. The composition and crystal structure of representative Ti3Sn0.8Al0.2C2 are examined by HRTEM, HAADF and EDS associated with STEM, and thus the Sn-rich Ti3(SnxAl1-x)C2 solid solution is confirmed. Combined with means of thermal analysis, the reaction path for the formation of the Sn-rich Ti3(SnxAl1-x)C2 solid solution is explored. Solid solutions are found to form with TiC as the nucleus and grow by reacting with Ti-Sn/Ti-Al intermetallic compounds. This work proves that the Ti3(SnxAl1-x)C2 over the whole composition range, in particular, the Sn-rich end of this series of solid solutions can be obtained by the simple pressureless sintering, and would enable the fine manipulation of the composition of these typical MAX solid solutions for technologically important applications. (c) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：Nanocrystalline Ni-Zn ferrite nanoparticles (NPs) NixZn1-xFe2O4 have been synthesized followed by detailed analysis of compositional effects on morphology, crystalline phase formation, lattice constant, crystallite size, magnetic, optical and dielectric properties describing the underlying physics as well. Cubic spinel structure with (311) preferred orientation and switching trend in crystallite size variation with gradual decrease in lattice parameter (from 8.377 to 8.323 angstrom) with the increase in nickel content has been observed through calculations. The magnetic behavior of NPs has been investigated at lower temperatures up to 5 K illustrating significantly improved magnetic parameters including M-s = 36.8 emu/g, M-r = 3.61 emu/g, SQ = M-r/M-s = 0.1028, H-c = 115.33 Oe, mu(B) = 1.5664 emu, and K-1 = 2122.18 erg/g. This enhancement has been found possibly due to less thermal fluctuations and significant superparamagnetic contributions from the very small fine nanoparticles being in blocking state owing to such a cool environment. Optical band gap for both direct (1.74-1.39 eV) and indirect (1.25-1.16 eV) transitions shows decreasing trend with the increase in Ni contents probably due to the redistribution of Ni or Zn contents from octahedral to tetrahedral site. Dielectric constant (real and imaginary) and tangent loss decreased with the increase of frequency, this refers to the Maxwell-Wagner type of polarization in the material in accordance with Koop's theory, however, a switching is observed at the stoichiometric ratio of x = 0.25 and 0.75. The impedance (Z') has maximum value 5539 k Omega at x = 0.75 and a minimum value 682 k Omega at x = 1.0. The Nyquist plot pointed out the contribution of grain boundaries, however the contribution varies with the stoichiometric ratio x. The Cole-Cole plot confirms the contribution of grains in the material for all value of x. (C) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：The macroscopic magnetic behavior of nanoparticulated systems is the result of several contributions, ranging from the intrinsic structural properties of the nanoparticles to their spatial arrangement within the material. Unravelling and understanding these influences is an important task to produce nano-systems with improved properties for specific technological applications. In this work we study how the magnetic behavior of a set of magnetically hard nanoparticles can be improved by the modification of the sample arrangement (either randomly or magnetically oriented) and the nature of the enclosing matrices. At first, we employed a hot-injection, continuous growth strategy to synthesize non-stoichiometric cobalt ferrite (CoxFe(3-x)O(4)) nanoparticles. We prepared five batches of hydrophobic, oleate-coated samples, with mean diameters of 8 nm, 12 nm, 16 nm and variable Co-to-Fe proportions. The structural characterization con-firms that the nanoparticles have a spinel-type monocrystalline structure and that the Co and Fe ions are homogenously distributed within the system. The magnetic properties of the nanoparticles were measured by DC magnetometry, and we found that the strategy used in this work to create a system of magnetically oriented nanoparticles can lead to a significant remanence and coercive field enhancement at low temperatures when compared with randomly oriented and fixed systems. The modification of the magnetic properties was detected in the five batches of samples, but the strength of the enhancement depends on both size and composition of the nanoparticles. Indeed, for the "hardest" samples the coercive field of the magnetically oriented systems reached values of around 30 kOe (3 T), which represents a 50% increase regarding the randomly oriented system and are among the highest reported to date for a set of Fe and Co oxide nanoparticles. (C) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：With the development of flexible electronic devices, various requirements for flexible conductive materials have been put forward to. However, the self-healing, mechanical and conductive properties of the flexible materials are poor. Therefore, it is important to prepare self-healing materials with good mechanical and conductive properties. In this paper, room temperature self-healing and conductive composites based on imine reversible covalent bond were prepare by introducing of the carbon nanotube and carbon black. The self-healing, mechanical and conductive properties of the composites were studied. And the structure of the composites was also characterized. The experimental results showed that the mechanical strength and the electrical resistivity of composites were 6.6 MPa and 108 Omega middotm, respectively. The composites have excellent room temperature self-healing properties through the reversible exchange of imine bond, and the healing efficiency of mechanical properties and the electrical properties can reach 96% and 93%, respectively. At the same time, the self-healing mechanism was put forward to. In addition, the composites can be recovered by solution recovery and hot pressing. (c) 2021 Elsevier B.V. All rights reserved.
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