查看更多>>摘要：The effect of Cu addition on the microstructural evolution and mechanical properties of hypoeutectic Al-10Mg_2Si alloys was investigated. It was found that Cu addition could effectively refine the primary a-Al grain. Simultaneously, the coarse eutectic Mg_2Si was also modified to be fine coral-like. The constitutional supercooling and the multiple nanosized precipitating layers at the edge of the eutectic Mg_2Si cause the branching and refining of the eutectic Mg_2Si through effectively restricting the growth of eutectic Mg_2Si, while the Cu-rich clusters and nanosized precipitates on the surface of the end of the eutectic Mg_2Si prevent the diffusion of the solute atoms such as Al, Mg and Si, and the growth of eutectic Mg_2Si grains is physically limited, resulting in the decrease of the length of eutectic Mg_2Si. The strength and ductility of the Cu-added Al-10Mg_2Si alloys were simultaneously improved, and the fracture failure mode transforms from brittle failure to ductile failure. The mechanism of mechanical properties enhanced by Cu addition was discussed.
查看更多>>摘要：Aqueous zinc-ion supercapacitors are a new type of energy storage device possessing high energy density, high safety, long service life, and abundant raw materials, which have attracted attention toward research. In this paper, NiCo_2O_4 nanosheets rich in oxygen vacancies were used as the cathode material for a novel aqueous zinc-ion supercapacitor. The aqueous zinc-ion supercapacitor device showed excellent electrochemical performance with a high specific capacity of 122.5 mAh/g at a current density of 1 A/g. The specific capacity of discharge at a current density of 10 A/g was found to be 72.6 mAh/g, along with a capacity retention rate of 59.3%. The reduction of NaBH_4 enhanced the content of oxygen vacancies in the materials, which facilitated the enhancement of the conductivity and electrochemical properties of the materials. The high energy density and high multiplier performance of the aqueous zinc-ion supercapacitors showed potential for wide applications in portable electronic products and smart devices.
查看更多>>摘要：Y_(0.9)Gd_(0.1)Fe_2, which crystallize in a C15 cubic structure, can absorb up to 5 H/f.u. and its pressure-composition isotherm displays a multiplateau behavior related to the existence of several hydrides with different crystal structures. At room temperature Y_(0.9)Gd_(0.1)Fe_2H_x hydrides (2.9 ≤x ≤ 5) crystallize in three phases with cubic structure (C1, C2 and C3), two phases with monoclinic structures (Ml and M2), and one phase with orthorhombic structure (0), with the following sequence for increasing H concentration: C1, M1, C2, M2, C3, O. Each phase exists as single phase within a H homogeneity range, and they are separated from each other by two-phase domains. The reductions of crystal symmetry are related to various hydrogen orders into interstitial sites. Weak superstructure peaks were indexed by doubling the cubic cell parameter of the cubic C2 phase. Upon heating, the monoclinic Ml and M2 and the cubic C2 phases undergo order-disorder (O-D) transitions toward a disordered cubic structure C_(Dis). These O-D transitions are reversible with thermal hysteresis effects. The cubic C3 and orthorhombic 0 phases transform into a disordered cubic phase accompanied by H desorption.
查看更多>>摘要：Interfacial defects and electrical characteristics were analyzed to confirm the formation of dipole due to the densification of the SiO_2 buffer layer and the resulting movement of the flat-band voltage. Through the NAOS, the SiO_2 layer was densified without any change in thickness, and the suboxide density after the NAOS decreased from 2.23 × 10~(14) atoms/cm~2 (PE-CVD) to 1.33 × 10~(14) atoms/cm~2 (PE-CVD+NAOS). In addition, both electrical and interfacial defects decreased after NAOS and PMA. From these results, the SiO_2 buffer layer through the NAOS was densified and the interface defect state density was reduced. The PE-CVD sample with low atomic density had a dipole layer strength of 0.799 V before PMA, but it was 0.457 V in the case of PE-CVD+NAOS with high atomic density due to the densification of the SiO_2 buffer layer. Also, both samples were reduced to 0.488 V and 0.422 V after PMA. Based on this, the leakage current of PE-CVD was measured to be 3.05 × 10~(-5) A/cm~2, and the leakage current of PE-CVD+NAOS was measured that the difference in about four orders of magnitude was 1.64× 10~(-9) A/cm~2. Through the densification of the SiO_2 layer, the interface atomic density increased, and consequently, the dipole layer strength decreased, thereby improving the electrical properties.
查看更多>>摘要：In this study, the microstructural and mechanical properties of NiCoCrAlSi high entropy alloy (HEA) fabricated by mechanical alloying and spark plasma sintering (SPS) method was studied. Initially, the starting powders with the composition of Ni_(28)Co_(26)Cr_(26)Al_(10)Si_(10) were subjected to mechanical milling at different times of 5,10,15, 20 and 40 h. The 40 h milled powder was then sintered by SPS method at 1170 °C. The microstructural characterization, phase analysis and mechanical properties of this sample were evaluated by field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), Rietveld analysis and tensile test. XRD results showed that by increasing the milling time the size of crystallites reduced and lattice strain increased. In addition, formation of FCC1 (F1) phase at final stages of mechanical alloying was observed. However, the peak of some of the remaining elements was still observed after 40 h of milling. After sintering, formation of FCC2 (F2) phase alongside Fl was observed. According to quantitative analysis, Fl phase with fraction of 89.3 wt% and F2 phase with fraction of 10.7 wt% is formed after SPS process. For this sample, a tensile strength of 1365 ± 141 MPa was obtained.
查看更多>>摘要：The influence of A-site Bi substitution on B-site cation ordering, crystal structure, and magnetic properties of La_(2-x)Bi_xNiMnO_6 double perovskites has been studied. Compounds with and without Bi substitution adopt monoclinic crystal structure with the P2_1/n space group as determined from the Rietveld refinement of x-ray diffraction data. X-ray photoelectron spectroscopy indicated an increase in Mn~(4+)/Mn~(3+) and Ni~(2+)/Ni~(3+) ratios in Bi substituted sample, and hence emphasized improved Ni and Mn ordering. This has been well supported by bond length analysis which suggested a compression in < Mn-O > and elongation in < Ni-O > bond lengths. The Bi substituted compound showed a relatively larger moment as compared to the parent sample, which was attributed to the suppression of antisite disorder i.e., enhanced Ni-Mn cation ordering due to Bi substitution. The temperature-dependent dc magnetization studies reveal a ferromagnetic to paramagnetic phase transition, and the Curie temperature has been observed to increases with Bi substitution. The critical exponent analysis around phase transition also confirmed the increase in the critical temperature for the Bi substituted compound. A detailed analysis of the critical behavior has been performed using different models, which suggested a long-range ferromagnetic ordering for both pure and Bi substituted samples.
查看更多>>摘要：ScAlMgO_4 is a promising material that can be used to fabricate lattice-matched substrates for the epitaxial growth of GaN and InGaN. To improve its crystal quality, we used synchrotron X-ray topography to study the dislocations in a 50.8-mm-diameter ScAUvlgO_4 single crystal grown via the Czochralski method. Dislocation character was analyzed in terms of Burgers vectors by comparing dislocation contrasts recorded using sixg-vectors that represented the m+c, a+c, and c-type crystal planes. The central area of the substrate, which corresponded to the portion grown vertically under the seed crystal, was characterized by millimeter-sized domains bound by mixed-type dislocation arrays with both in-plane and c-axis Burgers vectors. Basal plane dislocations (BPDs) typically formed an arrow-like shape with three branches. Growth striations with alternating high- and low-dislocation-density areas were observed in the diameter-expanding area and high-dislocation-density areas were covered with tangled BPD networks. The mechanisms of dislocation generation, multiplication, and reaction are discussed based on their line directions and dislocation character.
查看更多>>摘要：Complex boron substructures lead to diversity properties for transition metal borides (TMBs), that provides them many application possibilities in numerous fields. To clarify the actual effect of boron substructures on mechanical, magnetic and electrical properties, we prepared polycrystalline β-FeB samples with zigzag boron chains by high pressure and high temperature. β-FeB exhibits high saturation magnetization (79.54 emu/g), good antioxidant capacity (> 800 K), high hardness (15.62 GPa) and low resistivity (3.4 × 10~(-6) Ω m); thus, it is a promising magnetic material for extreme environmental applications. Subsequently, we performed first-principle calculations combined with X-ray photoelectron spectroscopy analysis and found that the free electrons transferred from Fe atoms stabilize the zigzag boron chains. Spin selection occurs during electron transfer and bonding, with majority spin state electrons as the main participants. The zigzag boron chain substructure provides excellent mechanical properties, at the expense of electrical and magnetic properties. Therefore, we speculate that the spin-selective electrons transfer between the metal and boron substructure can effectively modulate the electrical, mechanical, and magnetic properties of TMBs. This study introduces an effective route for the design, preparation, and applications of high-hardness multifunctional TMBs.
查看更多>>摘要：Hydrogen (H)- and deuterium (D)-loaded Mg_(0.25)Mn_(0.75) nanocomposites were prepared by a ball-milling process and Atom Probe Tomography (APT) analyses were carried out in order to investigate the resultant nanostructure. Due to the immiscibility of the Mg-Mn system, non-uniform and interconnected Mg-rich domains with a thickness of several to 10 nm formed in both of the H- and D-loaded composites. Such complex morphology could be attributed to the severe cold-rolling effects induced by ball-milling. The inhomogeneous distribution of D observed by the APT analysis is likely the result of severe lattice distortion and multiple defects, which are cold-rolling effects. While the detection of D in the D-loaded composite was hampered significantly by the desorption of D during specimen preparation, D remained around the boundary of the Mg-rich domains/Mn-rich matrix. This suggests that the modulated intermixing of immiscible Mg and Mn atoms together with the ball-milling effect results in a disordered atomic arrangement around the boundary. This is assumed to be one of the contributing factors in the destabilization of Mg hydride observed in our previous works.
查看更多>>摘要：Application of the super-wettability material is one of the most ideal approaches to achieve oil/water separation. The construction of the super-wettability material surface is the key to significantly boost the separation efficiency. In this work, the ZnO@Cu_2O honeycomb-likes hierarchical micro/nano-structure copper mesh (ZnO@Cu_2O/CM) is facilely fabricated through the combination of oxidation and hydrothermal deposition. Accordingly, superhydrophilicity/underwater superoleophobicity can be achieved, which endows over 99% separation efficiency as well as considerable permeation flux (>38120 L-m~(-2)-h~(-1)) for ZnO@Cu_2O/CM toward various oil/water mixtures. Besides, the combination of ZnO and Cu_2O produces a p-n heterostructure to further reduce the recombination rate of electron and hole, resulting in the improved the photocatalytic activity. The removal efficiency for methylene blue (MB) of ZnO@Cu_2O/CM could be improved to 98.1%, nearly 1.6 times than that of Cu_2O/CM. Various stability tests demonstrate that the material exhibits good mechanical stability, anti-corrosive property and thermal durability under harsh environments. Furthermore, cyclic experiments reveal that ZnO@Cu_2O/CM exhibits fascinating reusability. In conclusion, the as-synthesized dual-functional mesh performs favorable photocatalytic activity and super-wettability, which can realize wastewater remediation at low cost and energy consumption.
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Elsevier