查看更多>>摘要：Fe-based bulk metallic glass (BMG)(FeCrMoWMnSiBC) was produced by selective laser melting (SLM) successfully in this study. The best parameters were determined through extensive experiments. The relative density (95%) and amorphous rate (95.47%) samples were obtained by this parameter. The analysis of the microstructure reveals that the crystalline phases in the heat affected zone (HAZ) are mainly ix-Fe and M-23(CB)(6) phases, and co-exist with the amorphous phases. The Heat treatment is employed to study the crystallization behavior of amorphous phases. The ix-Fe phase, as the primary phase, grows into a submicron crystal phase under the action of multiple thermal cycles. Nanoindentation test results show that the hardness of the amorphous phase is higher than that of the nano-grain region, and the hardness of the nanocrystalline region is higher than that of the submicron-grain region. The free volume content is different and the amorphous phase is not uniform due to the complex thermal cycle. The maximum hardness occurs in the amorphous phase with 22.6 GPa. (C) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：In this work, a series of binary metal sulfides with well-defined two-dimensional (2D) nanosheet structures are in situ achieved on nickel foams (NF) via a one-step electrodeposition strategy under ambient conditions, which directly serve as effective electrodes for oxygen evolution reactions (OER) from water splitting. These NiFeS@NF nanosheets require a low overpotential of only 243 mV to deliver a current density of 10 mA cm(-2), superior to that of NiCoS@NF and FeCoS@NF synthesized under the same conditions. The mechanism by which the OER kinetics are enhanced is investigated in detail, where the unique 2D nanosheet architectures and Fe incorporation play a significant role. This hassle-free approach reported here contributes to an inexpensive and convenient access to the fabrication of effective nanocatalysts that can preclude harsh synthetic conditions such as high temperature and high pressure. (C) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：Bismuth molybdate (Bi2MoO6) is a multi-elemental metal oxide of the molybdate series, which could show great potentials for the application of gas sensors with outstanding sensitivity. Oxygen vacancy is a ubiquitous defect in this class of materials, and their introduction may be an effective strategy to regulate gas sensing performance. In this work, coupling investigations of experiment and first-principles calculations were performed to gain insight into the effect of oxygen deficiency on the gas-sensitive properties of Bi2MoO6. The oxygen vacancies existed in surface lattice changes the adsorption reaction pathway of the gas by modifying the coordination state and geometry of lattice oxygens, which is more favorable for the adsorption or dissociation of target gas and oxygen molecule. Further, the oxygen-deficient Bi2MoO6 was synthesized experimentally by a one-step solvothermal method. The gas sensor based on the oxygen -deficient Bi2MoO6 could respond to NH3 gas sensitively and selectively, with a high response value of 53.97 (5 ppm) at the optimal temperature of 75 degrees C. Combining the clarifications by first-principles calculations, the satisfactory sensing performance exhibited experimentally could be understood based on the promotion of adsorption activity and adsorption capability. (C) 2021 Elsevier B.V. All rights reserved.
Mitroshenkov, N. V.Matovnikov, A. V.Kuznetsov, S. V.Lazutkina, M. V....
9页
查看更多>>摘要：Temperature dependences of the heat capacity C-p(T) (2-300 K) and lattice parameter a(T) (5-300 K) of LaF3 and (SrF2)(0.5)(LaF3)(0.5), in addition to the earlier studied SrF2, are experimentally investigated for the first time. The experimental dependences of C-p(T) and the unit cell volume V(T) of the studied fluorides are analysed using the Debye-Einstein model considering the influence of the disorder of their crystal structures. The parameters of the model are determined. An anomalous arrangement of the C-p(T) and V(T) curves of the solution with respect to the corresponding curves of the components is revealed. At low temperatures (T < 150 K), the values of C-p(T) and V(T) of the solution exceed the values calculated by the additivity rule. At higher temperatures (T > 150 K), deviations towards smaller values are observed. We have established that the disorder in solid-solution crystal structure is the common reason of anomalies revealed. It is found that at low temperatures, the cause of these anomalies is a decrease in the vibrational frequencies in the solid-solution metal sublattice upon the replacement of Sr with La, which has a large size and mass. Such a replacement leads to distortions of the original structure and an increase in its disorder. At elevated temperatures, the deviations are caused by an increase in the vibrational frequencies in the F- sublattice due to distortion of the crystal structure, as well as the increased influence of the anharmonicity of the disordered crystal lattice vibration. (C) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：Magnesium, the lightest structural metal, has limited industrial application due to its poor formability at room temperature. However, the mechanism for the effect of alloying elements on formability has not yet been clarified. To deduce this effect, we study recrystallization, a phenomenon that occurs in the last stage in the manufacturing process, of Mg-Al-Zn and Mg-Zn-Ca solid solutions, which show recrystallization behaviors similar and different to that of pure Mg, respectively. By developing a new atomistic simulation method of migrating grain boundaries in hcp structure materials, we investigate the representative recrystallization phenomena occurring in solid solutions: grain boundary segregation, solute clustering, and grain boundary migration. It is found that the grain boundary segregation occurring in both ternary Mg alloys is not synergistically stronger than those in their constituent binary Mg alloys, but is sufficient to retard the onset of the grain boundary migration. However, solute clusters are actively formed only in the Mg-Zn-Ca alloys and strongly drag grain boundaries during the migration, which strengthens the dragging effect of the Mg-Zn-Ca alloys compared to that of the Mg-Al-Zn alloys. The strong dragging effect originated from solute clusters could be another cause of the change in the recrystallization behavior of Mg alloys. (c) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：Recently, SnSe of orthorhombic phase has attracted much attention due to its excellent performance in thermoelectricity, yet the thickness-dependent thermoelectric properties were poorly studied. We have investigated the thermoelectric transporting properties of few-layered (from 1 L to 4 L) and bulk SnSe by using density functional theory plus Boltzmann transport theory. We employed the electron-phonon Wannier method to obtain the accurate transporting parameters, i.e., carrier mobility as well as relaxation time, in contrast to those derived from deformation potential theory. Our results reveal that the band gap decreases from 0.91 eV (1 L) to 0.59 eV (bulk) as the thickness increases, and meanwhile the effective charge mass increases slightly. As bulk SnSe is thinned to the monolayer, the high frequency modes are stiffened while the low frequency modes are softened, and meanwhile the acoustic velocities become larger. At 300 K, the thermal conductivity of bulk SnSe takes 1.52, 0.80 and 0.41 W m(-1) K-1 for kappa(a), kappa(b) and kappa(c) respectively, in good agreement with the experimental values. Thermal conductivity of few-layered SnSe decreases slightly from 2.45 to 1.61 W m(-1) K-1 for kappa(a), and from 1.81 to 1.02 W m(-1) K-1 for kappa(b) as the layer number increases from 1 L to 4 L. The EPW calculations reveal that the electron mobility of n-type films increases rapidly from 24.4 cm(2)/V s (1 L) to 179.6 cm(2)/V s (4 L) and the hole mobility of p-type films increases from 47.2 cm(2)/V s (1 L) to 1211.1 cm(2)/V s (4 L) at 300 K as the thickness increases. Compared with the monolayer, thicker film of SnSe has larger carrier mobility as well as lower thermal conductivity, which leads to better thermoelectric performance. At 700 K, the figure of merit is enhanced from 0.22 (1 L) to 0.58 (4 L) for n-type films in electron density of -0.55 x 10(13)/cm(2). Our research casts some light on the future thermoelectric applications based on few-layered SnSe. (C) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：Herein, to enhance the long-term stability, ZnO varistor ceramics mixed with Bi2O3, Sb2O3, MnCO3, Co2O3, SiO2, and different concentrations of NiO (with 0, 0.3, 0.7, 1, 1.3, 1.6 mol%) were grown for controlling the Bi2O3 intergranular phase as alpha-Bi2O3 using a well-known ceramic process technology. The microstructure and crystalline phases were investigated using scanning electron microscopy (SEM), X-ray energy dispersive spectrometry (EDS), X-ray diffraction (XRD), and transmission electron microscopy (TEM). The electrical properties were evaluated using a high-voltage DC power supply, current pulse generator, oscilloscope, and impedance analyzer. Results from XRD patterns and TEM indicated that the NiO dopant enables the transition of delta- to alpha-Bi2O3 phase. Current density-electric field measurements revealed that NiO-doped ZnO ceramics have an increased breakdown field and decreased leakage current density. During DC aging, the power loss-aging time curves of NiO-doped ZnO ceramics with increased alpha-Bi2O3 phase showed a downward trend, indicating increased stability. The current research has revealed that improving the electrical stability of polycrystalline ceramics via intergranular phase control might be feasible for the emerging DC power-based aging applications. (C) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：Herein, we reported two alkali metal molybdenum(VI) iodates, namely, NaMoO3(IO3) and gamma-KMoO3(IO3) with 1D and 3D [MoO3(IO3)]- anionic architectures, respectively. The novel 1D chain in NaMoO3(IO3) and the 3D network in gamma-KMoO3(IO3) are constructed by the 0D A-shaped cis-[MoO4(IO3)2]4- building units interconnected by bridging IO3- anions as well as the corner-sharing of oxo anions. Importantly, the polar gamma-KMoO3(IO3) exhibits a very large second-harmonic generation (SHG) effect of 12 x KH2PO4 (KDP) under 1064 nm laser radiation, a high laser-Induced damage threshold value (52 x AgGaS2), and a moderate birefringence of 0.087@1064 nm, whereas the centrosymmetric NaMoO3(IO3) has a large birefringence of 0.208@1064 nm. This study further proves the useful route of exploring promising optical materials via assembling the 0D basic building units into higher dimensional anionic architectures. (c) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：Lithium-ion batteries have high potential to be used as energy storage devices for wearable electronics due to their high energy density, high output voltage and environmental benignity. The increasing demand to develop wearable electronics has aroused great interests for flexible anode of lithium-ion batteries. However, the traditional rigid anode severely hiders further development of lithium-ion batteries in flexible wearable devices. Herein, we demonstrated a flower-like architecture material, in which the layered MoS2 nanosheets are anchoring on 3D porous carbon nanofibers (CNFs), serving as free-standing anode for LIBs, and this material can be wound at will. The free-standing CNFs were prepared through a facile electrospinning and carbonization process, the MoS2 nanosheets consist of few MoS2 <= 5 layers and were prepared through a hydrothermal process. Time-dependent experiment illustrated that the flower-like architecture was transformed from bare fibers and tiny particles. Although the polymers were stretched, shrank and covered by MoS2 nanosheets in the fabrication proess, the membrane still retained excellent flexible from beginning to end. Benefiting from the coaxial structure and synergistic effect, the flexible anode delivered an initial high discharge capacity (938.8 mAh g(-1), 0.2 A g(-1)) and outstanding capacity retention rate at high current density (457.2 mAh g(-1), 2 A g(-1), 276.3 mAh g(-1) after 1000 cycles). Its stability can surpass other flexible MoS2-based anodes. Furthermore, the hybrid electrode can maintain superior flexibility and mechanical stability after experiments, guaranteeing a promising future in wearable electronics. This work indicates that the flexible MoS2 @CNFs can be used as anode for flexible batteries, flexible capacitors and other wearable applications. (C) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：beta-Ga2O3 films have been prepared on sapphire (0001) substrate using an RF magnetron sputtering. The highly oriented beta-Ga2O3 films with a high crystallinity could be obtained at Ts above 700 degrees C. The sputtered film in pure Ar showed a low optical band-gap and a strong optical absorption in UV and visible region, possibly due to non-stoichiometry, oxygen-deficiency. Raman modes of beta-Ga2O3 started to evolve at Ts of 400 degrees C and then, were clearly defined and dominant at Ts above 600 degrees C in a good consistence with XRD result. In the PL spectra at Ts above 600 degrees C, UV emission peaked at 3.75 eV and red-emission composed of broad band and sharp peaks were predominant. These emissions are the first report in PL spectra of beta-Ga2O3 and have been tentatively assigned to high energy excitons caused by electrons trapped with holes at deeper acceptor level, and optical transition between deep donor level and delocalized/clustered acceptor levels, respectively. (C) 2021 Elsevier B.V. All rights reserved.
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