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：The development of ABO_3 perovskite-structured dielectric materials with high recoverable energy storage density (V_(rec)) and power density (P_D) is crucial for the downsizing of pulsed power devices. Despite several research efforts, achieving a high W_(rec) over a wide working temperature range in an environmentally benign system remains a difficulty. A synergistic design strategy is given here, which includes concurrently doping at the A- and B-site to achieve a spread and depressed dielectric response, adding sintering aids, and employing advanced viscous polymer rolling technology for dense and ultra-thin ceramic samples, respectively. Finally, at a relatively low electric field of 380 kV/cm, an ultrahigh W_(rec) of 6.57 J/cm~3 is realized in (Bi_(0.5)Na_(0.5))_(0.93)Ca_(0.07)Ti_(0.85)Zr_(0.15)O_3-0.5 wt% Li_2CO_3 component, which benefits from gentle polarization saturating and improved breakdown strength. The W_(rec) can be maintained above 6 J/cm~3 while maintaining strong thermal stability (variation ≤ ± 3%) over a temperature range of 30-150 °C. Because BNT-based materials have such high energy storage performance and temperature stability, they are not only a promising candidate for replacing lead-based dielectrics, but also a valuable guide for developing new high-performance ferroelectric materials for future energy storage devices in the pulsed power system.
查看更多>>摘要：Transition metal dopant engineering and rational architecture design have been proven to be effective strategies to improve the electrochemical energy storage properties of electrodes. Herein, V-doped NiMn-layered double hydroxide composites were supported on reduced graphene oxide-coated Ni foam (NMV-L/ rGO) by a hydrothermal method. The influences of V content on the electrochemical performances of NMV-L/rGO composites were investigated in detail. At an optimal content of V doping (15%), the NMV-L/rGO-15 reveals enhanced electrochemical properties, and it is subsequently applied as the substrate for the elec-trodeposition of Ni_3S_2 layer. Benefiting from the collaborative effect of NMV-L/rGO-15, Ni_3S_2, and rGO materials, as well as the unique hierarchical architecture, excellent electrochemical performance is obtained in the as-prepared Ni_3S_2 @NMV-L/rGO-15 composite, which exhibits a high specific capacity of 1412.0 C g~(-1) at 1 A g~(-1) as well as desirable long-term stability of 89% over 5000 cycles. Furthermore, the as-fabricated battery-supercapacitor hybrid device (BSH) based on Ni_3S_2@NMV-L/rGO-15 and activated carbon (AC) electrodes displays a remarkable energy density of 60.0 W h kg~(-1) at the power density of 849.1 W kg~(-1) and superior capacity retention of 96% through 7000 cycles. Such excellent results indicate that the Ni_3S_2 @ NMV-L/rGO-15 composite holds great potential as electrode material for high-performance BSHs.
查看更多>>摘要：As a burgeoning energy storage equipment, more attention has been paid to sodium ion hybrid super-capacitor (Na-HSC) with large energy/power density and long cycle life. Anode materials with high Na~+ embedding rate are the key for its development. In this work, multi-chamber microspheres with Nb_2O_5 quantum dots (T-Nb_2O_5@YC) were prepared from yeast enriched with Nb~(5+) and by simple hydrothermal-carbonization. Na~+ half-cell and Na-HSC have excellent electrochemical performance. To be specific, Na+ half battery with T-Nb_2O_5@YC delivers up to 195.7 mA h g~(-1) and maintains 84% discharge capacity after 2000 cycles. Moreover, Na-HSC assembled with T-Nb_2O_5@YC as anode has high energy density (62.5 Wh kg~(-1)) and power density (1250 W kg~(-1)).
查看更多>>摘要：ZnO has a large band gap, which affects its photoelectric catalytic performance to a certain extent. In this paper, Bi-doped ZnO nanoarray was successfully prepared by electrochemical deposition to improve the photoelectrochemical performance of ZnO as a photoanode. XRD results show the prepared Bi-doped ZnO is a typical hexagonal wurtzite crystal, and the SEM results also proved this point. The prepared Bi-doped ZnO presents a neat nano-array, and the doping of Bi also reduces the diameter of the nanorods from the original 500-350 nm. The results of XPS show that Bi is successfully doped into the ZnO nanoarrays, and it exists in the form of Bi_2O_3. Subsequently, the prepared Bi-doped ZnO was analyzed by fluorescence spectroscopy and photoelectrochemical properties, and it was found that when the doping concentration was 5%, the fluorescence intensity was the lowest, and at this time the carrier recombination rate corresponding was the lowest, the photoelectric catalytic effect was the best.
查看更多>>摘要：The stacking fault energy y of an alloy has been reported to significantly affect the grain size d and twin nucleation size r_c during grain refinement. However, ternary relation among y, d and r_c has not been investigated comprehensively. Here we prepared nanocrystalline (NC) and ultrafine-grained (UFG) 99.99 wt% Cu, Cu-0.86 wt% Al and Cu-2.2 wt% Al alloys with different y by high-pressure torsion (HPT), and then characterized d and r_c. Transmission electron microscopy observations show that under the same experimental condition d decreases and corresponding grain refinement mechanism transforms from dislocation subdivision to twin segmentation with decreasing y. The relation among y, d and r_c from experiments are consistent well with theoretical prediction from Meyers model. r_c decreases with decreasing d, and the variation is exacerbated by the decrease of y. r_c increases first and then decreases by forming a peak-shaped variation with decreasing y when d is in UFG regime, suggesting there exists an optimum stacking fault energy r_c for twin nucleation. The r_c peak becomes flat and moves to higher y value when d is in NC regime due to the enhanced geometric effect of d on r_c which weakens the role of y. Our findings reveal a comprehensive ternary relationship among y, d and r_c, and provide guidance for designing NC and UFG materials with high-density twins and good strength-ductility combination.
查看更多>>摘要：Hexaferrites are usually used in devices for frequencies of 8-75 GHz. In this work, it is shown that Sn-substituted hexaferrite can be used for electromagnetic shielding and at lower frequencies (for example, in the L-band and S-band) as absorbing materials. The paper defines a solid-state reaction technique for preparing BaFe_(12-x)Sn_xO_(19) (0.1 ≤ x ≤1.2). The samples are characterized by XRD, SEM, VSM, and VNA. The study shows that increasing the Sn-substitution leads to weakening the interaction between the magnetic sublattices. So, in general, the saturation magnetization (M_s) decreases. Low saturation magnetization at high coercivity values gives a high anisotropy field, which provides significant absorption and matching impedance. The sample with substitution of x = 1.2 is the most absorbing sample (more than 99.99% of the incident energy absorbed for 10 mm thickness). The investigated samples have the potential to be useful absorption materials for shielding production (materials that absorb electromagnetic radiation)
查看更多>>摘要：The synergistic effect of Zr addition and grain refinement on the corrosion resistance and pitting corrosion behavior of single α-phase Ti-Zr-based alloys was evaluated. The corrosion mechanisms of as-cast and hot-rolled Ti-xZr-4Al-0.005B alloys (x = 0,10, 20, 30, 40 wt%) in 5 M aqueous hydrochloric acid solution are investigated by analyzing their electrochemical and immersion corrosion behavior using scanning electron microscopy, electrochemical analyses, and X-ray photoelectron spectroscopy. Both Zr alloying and grain refinement improve the corrosion resistance; while grain refinement improves the stability of the passivation film, Zr addition increases the pitting sensitivity. Zr alloying and grain refinement greatly affects the pitting corrosion behavior in the alloy. In Ti or Ti-Zr alloys with low Zr content, grain refinement inhibits the appearance of corrosion pits inside the grains. For Ti-Zr alloys with higher Zr content, grain refinement induces small corrosion pits in the alloy. Grain refinement increases the frequency of corrosion pits in the Ti-Zr alloys with higher Zr content but inhibits the growth of the pits by improving the corrosion resistance and stability of the passivation film through the formation of more high-valence oxides and a thicker passivation film.
查看更多>>摘要：Constructing Z-scheme heterojunction is considered to be a promising strategy to isolate photogenerated carriers and boost the activity of the photocatalysts. Here in, a novel Z-scheme Bi_2WO_6/Ni-MOF heterojunction with intimate interface was constructed via wrapping flowerlike Bi_2WO_6 on 2D Ni-MOF sheets. The resultant Bi_2WO_6/Ni-M0F heterojunction displayed superior photocatalytic performance with respect to methylene blue degradation under visible light illumination. When the content of Ni-MOF was 20 wt%, the Bi_2WO_6/Ni-M0F heterojunction achieved the highest activity, which was 24.0 and 6.4 folds that of the pristine Ni-MOF and Bi_2WO_6, respectively. The superior degradation performance was caused by the formation of a direct Z-scheme heterostructure between Ni-MOF and Bi_2WO_6, which boosted the separation of photoinduced carriers. The principal active species and possible photocatalytic mechanism were also explored. This study provides a pathway to design and fabricate efficient Z-scheme photocatalysts for environmental remediation.
查看更多>>摘要：ZnSn(OH) _6/ZnO/BiOBr (ZHS/ZnO/BOB) and ZHS/ZnO/BOB loaded carbon fiber cloth (CFC) (ZHS/ZnO/ B0B@CFC) photocatalysts were successfully prepared by co-precipitation and ultrasonic method. The ultraviolet-visible diffuse reflection (UV-vis DR) spectra showed that the absorption edge of ZHS/ZnO/BOB exhibits red-shift to the visible light region, compared with the ZHS/ZnO. The conduction band position (E_(CB)) of ZHS, ZnO, and BOB were calculated to be - 0.12, - 0.22, and 0.36 eV vs. NHE, respectively, according to the Mott-Schottky (M-S) measurement. ZHS/ZnO/BOB presents flower-like spheres assembled from nanosheets. Brunauer-Emmett-Teller (BET) tested the specific surface areas of ZHS/ZnO/BOB (21.01 m~2 g~(-1)). Based on the photoluminescence spectroscopy (PL) and electrochemical impedance spectroscopy (EIS) analysis, ZHS/ZnO/BOB possesses the strongest ability to inhibit electron-hole pair recombination and the lowest charge transfer resistance, which can be mainly ascribed to the formation of heterojunction among ZHS, ZnO, and BOB. The ZHS/ZnO/BOB exhibits a high photocatalytic degradation activity for rhodamine B (RhB, 97.30%), tetracycline (TC, 83.00%), and levofloxacin (LVX, 74.50%) under 80 min irradiation, respectively. Besides, ZHS/ZnO/BOB@CFC achieved 98.8% removal efficiency towards RhB. Furthermore, high-resolution mass spectrometry (HRMS) revealed the possible degradation pathway of RhB during the photocatalysis process. Based on all the above, an easy approach for rational design of ternary photocatalyst towards the degradation of refractory pollutants was proposed.
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Elsevier