查看更多>>摘要：N-doped open hollow carbon structure is superb electrode material for supercapacitors due to its unique structure; however, it is often synthesized in an inert atmosphere at high temperature to be protected oxidation, resulting in massive inert gas consumption. Herein, a salt shielding strategy is developed to synthesize N-doped open hollow carbon structure by pyrolysis of zinc-containing zeolitic imidazolate framework at high temperature in air, saving massive inert gas. ZIF-8 template as well as the corrosion of molten salt and oxygen on the carbon structure is demonstrated to play the major role on the formation of the open hollow structure with a high specific surface area of 1589.23 m2 g?1. Applied as electrode material for symmetrical supercapacitors, as-sythesized carbon structure exhibits a high three-electrode specific capacitance of 339 F g?1 at 1 A g?1, a two-electrode capacitance performance of 315 F g?1 at 1 A g?1 and a long-term cycling stability with 98.9% of initial capacitance retention undergo 20 000 cycles at 5 A g?1 in 1 M H2SO4. This salt shielding strategy may be expanded to other non-oxide material synthesis field for energy storage applications to solve the bottleneck problems in industrial production.
查看更多>>摘要：In this study, α-Fe2O3@CoFe2O4 core-shell nanoparticles were synthesized and decorated on graphene oxide (GO) sheets with two ratios (3:1) and (5:1) for α-Fe2O3@CoFe2O4 to GO. FESEM images indicate a uniform distribution of α-Fe2O3@CoFe2O4 on the surface of GO, especially for (3:1) ratio. The α-Fe2O3@CoFe2O4/GO magnetic nanocomposite exhibits multiple magnetic resonances, strong interfacial polarization, multi reflection and scattering of incident microwaves, thus superior absorption properties. This is due to the structure, which provides various interfaces, high specific surface area, and multiple magnetic components. The microwave absorption properties are evaluated in the frequency range 8–18 GHz (X and Ku bands). Our results show that α-Fe2O3@CoFe2O4/GO (5:1) has the highest reflection loss, ?81.24 dB, at 11.98 GHz with a thickness of only 1.4 mm and bandwidth of 3.78 GHz. Interestingly, α-Fe2O3@CoFe2O4/GO (3:1) shows a remarkable broad absorption bandwidth of 8.91 GHz for a thickness of 3.4 mm, having reflection loss, ?75.14 dB at 10.25 GHz. The present results confirm that the prepared nanocomposites have promising potential applications in broadband absorption.
查看更多>>摘要：Single crystals of undoped and Ce3+, Tb3+, and Eu3+/Tb3+/Ce3+ co-doped Ba12(BO3)6[BO3][LiF4] crystals were grown from high-temperature solutions. The Ba12(BO3)6[BO3][LiF4] compound crystallizes in the structural type of barium orthoborate Ba3(BO3)2 with porous Ba12(BO3)66+ cationic framework filled with disordered anionic groups. The PL and PLE spectra of undoped and rare-earth-doped crystals were studied. The photoluminescence temperature dependences in the range of 77–300 K were recorded. The shape and position of lines in the spectra are typical of cerium, terbium, and europium ions. Luminescence lifetime constants were measured in the range of 77–300 К. It was shown that at the excitation wavelength of 300 nm and 370 nm at 300 K, Ba12(BO3)6[BO3][LiF4]:Eu3+, Tb3+, Ce3+ crystals have luminescence close to daylight with CIE chromaticity coordinates and correlated color temperature of (0.335; 0.309), 5352 K and (0.295; 0.362), 7121 K, respectively. Our results indicate that rare-earth-doped Ba12(BO3)6[BO3][LiF4] crystals can be considered a candidate for the conversion of LED emission into white light.
查看更多>>摘要：The noble metal substrate components and geometries have a critical effect on surface enhanced Raman spectroscopy, for ultra-trace molecular detection. In present work, Au-Ag alloy nanostars were synthesized, and homogenously assembled on silica optical fibers for fiber probes fabrication. The Au-Ag alloy nanostars were controlled synthesized by the ratio of Au and Ag. The fiber probes with uniform and dense distribution of Au/Ag alloy nano-stars were fabricated through PVP dispersant addition in metal nanostructure solution and fiber surface siliconizing. The limitation of detection of fiber probes for crystal violet (CV) and Rhodamine 6 G (R6G) are 10?9 M and 10?8 M, respectively, under 633 nm laser excitation. The relationship between analyte concentrations and Raman intensities showed nearly linear, which indicates potential applications for quantitative analysis. In addition, the fiber probes showed well reproducibility, with maximum 8.43% deviation from different probes. The electromagnetic field distribution simulation revealed much stronger electric field from nanostar tip top than sphere nanoparticles, even greater field from closed and crossed tip top between two nanostars, which was responsible for the high sensitivity of the fiber probes. The fiber probes could be applied for ultra-trace, single molecular detections for chemistry, biology and others.
查看更多>>摘要：In this work the effect of cooling rate on the dual-phase (L12/B2) AlCoCrFeNi2.1 Eutectic High-Entropy Alloy was investigated. AlCoCrFeNi2.1 powders were made using a drop-tube facility, achieving powders of sizes ranging from 850 μm ≤ d < 1000–38 μm ≤ d < 53 μm with corresponding estimated cooling rates of 114 Ks?1 to 1.75×106 K s?1 respectively. Average interlamellar spacing decreases from 2.10 μm in the as-cast alloy to 348 nm in the powders of the 38 μm < d < 53 μm size fraction. Although decreased interlamellar spacing is expected to enhance microhardness, such a relation was not as strong as expected, with microhardness of the powders found to vary only slightly from an average value of 340 Hv0.03. This unexpected result is explained via the observation of increased FCC volume fraction. With increasing cooling rate, the microstructure of AlCoCrFeNi2.1 was found to evolve gradually from regular eutectic to colony eutectic, followed by dendritic with eutectic the interdendritic regions. In particles of size d < 212 μm BCC dendrites were observed, either dominating the structure or coexisting with FCC dendrites.
查看更多>>摘要：A new type of AlCuFeMnTiV lightweight high entropy alloy (LWHEA) was prepared by mechanical alloying (MA) and spark plasma sintering (SPS). The effects of milling time on the phase evolution of alloy powders and sintering temperature on the microstructure and mechanical properties of alloy blocks were investigated. The results show that the powders can be alloyed after 36 h high-energy ball milling, forming a BCC solid solution, and the alloying sequence is related to the melting point of the alloy elements. After being sintered by SPS, the alloy block is mainly composed of the BCC matrix, and the B2 phase (ordered BCC phase) and the HCP phases are precipitated from the matrix during the sintering process. Besides that, the Cu-rich FCC phase is distributed at grain boundaries. Nano twins are found in some FCC phases, which have a good strengthening effect on the grain boundary so that the alloy maintains high strength and good plasticity. The block sintered at 1050 °C exhibits the best comprehensive mechanical properties, with the density of 6.28 g?cm?3, hardness of 618.44 HV, compressive strength and yield strength of 2630 MPa and 2060 MPa respectively, the plastic strain of 15.83% and specific strength of 418.79 MPa?cm3?g?1, which is superior to most LWHEAs and traditional lightweight alloys.
查看更多>>摘要：The design of composites rich heterogeneous interfaces to enhance interfacial polarization is an effective way to boost electromagnetic waves (EMW) absorption performance. In this work, multi-component electromagnetic ZnFe2O4/Fe/Fe4N/N-doped carbon (ZnFe2O4/Fe/Fe4N/N-C) composites were successfully fabricated by carbonization of core/shell/shell ZnFe2O4 @PDA@PPy precursors at 800 °C under a N2 atmosphere. The ZnFe2O4/Fe/Fe4N/N-C composites exhibit excellent low-frequency EMW absorption performance: the effective absorption bandwidth reached 8.41 GHz (3.57–11.98 GHz), covering the entire C-band (4–8 GHz) and X-band (8–12 GHz) at a thickness of 4.5 mm with a minimum reflection loss (RLmin) of ?36.13 dB at 4.54 GHz. The excellent property was attributed to the abundant heterogeneous interfaces in the ZnFe2O4/Fe/Fe4N/N-C composites with maximized polarization loss. Further, magnetic loss were enhanced by the introduction of Fe4N. This work demonstrates that the creation of heterogeneous interfaces via adding extra components is an effective strategy in the design of efficient low-frequency EMW absorbers.
查看更多>>摘要：The materials with topological phases have been a flexible platform for the realization of novel types of quantum matter due to their unique topology protected electron states. Herein, we report a comprehensive structural and electrical transport investigations on a topological insulator, SnBi2Te4, under high pressures by using diamond anvil cell techniques. Through in situ high pressure synchrotron x-ray diffraction studies, two structural phase transformations have been revealed. The powdered samples of SnBi2Te4 transform from the initial layered quasi-two-dimensional structure (phase I) to a monoclinic C2/m structure (phase II) at about 7.14 GPa, and eventually develop into a site-disordered body centered cubic structure (phase III) at pressures above 18.9 GPa. Modifications of the electronic band structure have been discovered by the in situ high-pressure electrical measurements at low temperatures. It is noteworthy that three distinct pressure induced superconducting states have been observed, one in phase II and two in phase III. In each of the pressure induced superconducting states, the critical temperature Tc decreases with pressure. The maximum value of Tc is obtained in the third superconducting state emerging at the highest pressure range, which is 8.9 K at 22.3 GPa. A deep understanding of the relationship between the pressure induced structure-dependent superconducting states and the ambient-pressure topologically insulating state of SnBi2Te4 may shed light on the universal physical nature that creates topologically insulating or superconducting states.
查看更多>>摘要：Recently, coupling agents have gradually been applied to perovskite solar cells (PSC) due to their interface modification properties. In this work, Ti3C2Tx MXene nanosheets with different amounts of silane coupling agent vinyltris (2-methoxyethoxylsilane) (SCA) (0, 0.1, 0.3, 0.5, and 0.7 V/V%) were deposited by spray technique as the hole transport layer (HTL). Taking the advantage of SCA, the interface distribution of Ti3C2Tx after film formation is effectively modulated, while flat, pin-hole free Ti3C2Tx films were obtained with a mixing content of 0.3 V/V%. Superior hole transfer path, enhanced hole extraction, and reduced transfer resistance at the HTL/perovskite interface were achieved due to the better formation of Ti3C2Tx films, thus leading to an increase in power conversion efficiency (PCE) from 11.12% to 13.65%. This work represents an effective method to improve the quality of Ti3C2Tx-based films and provides more possibilities for future research on Ti3C2Tx MXene.
查看更多>>摘要：MoNbTaW is a promising refractory multi-principal element alloy (RMPEA) that has exhibited good high temperature phase stability in vacuum and exceptional high temperature mechanical properties—even surpassing those seen in Ni superalloys. To date, there have been no detailed studies regarding the environmental resistance of this alloy, which is a primary concern due to the constituent elements being readily oxidizable at elevated temperatures. Therefore, in the current work, in-air anneals of sputtered MoNbTaW films targeting the 200°C–400°C range were conducted to study the low temperature oxidation behavior. An amorphous oxidized layer, which was comprised of three compositionally distinct regions, was observed to form at all in-air annealing temperatures. Furthermore, via nanoindentation, the oxidized layer was determined to be significantly softer and more compliant than the underlying metal. Comparison to pure W samples under the same annealing conditions was also performed. From this, it was determined that MoNbTaW oxidized more quickly and exhibited different oxidation pathways than pure W in the studied temperature range. Through this work, the initial stages of oxidation and their impact on the mechanical properties in this alloy system can begin to be understood.
NSTL
Elsevier