查看更多>>摘要：(l-x)Ca_(0.8)Sr_(0.2)TiO_3-xSmAlO_3 (abbreviated as (l-x)CST-xSA) perovskite ceramics were synthesized through the conventional solid-state reaction process. The effects of SmAlO_3 on the microstructure, low-frequency dielectric performances, and microwave dielectric properties for (l-x)CST-xSA ceramics were investigated systematically. All compositions exhibited an orthorhombic perovskite structure with dense surface morphology. With increasing the content of SmAlO_3) the order of B-site cation revealed a trend of increase first and then slowly decreased. The presence of oxygen vacancies in the (l-x)CST-xSA ceramics was detected by using x-ray photoelectron spectroscopy. Excellent temperature stability of dielectric permittivity and low dielectric loss (tan<5 lower than 0.005) were observed for (l-x)CST-xSA ceramics at low frequencies. For x = 0.35 composition, the temperature coefficient of the resonant frequency approached zero. In addition, the dielectric permittivity of 42.0, the quality factor of 39,120 GHz, and the temperature coefficient of resonant frequency of - 6.4 ppm/°C were obtained for 0.65CST-0.35SA ceramics. It is suggested that (l-x)CST-xSA ceramics can be used as a candidate material for various microwave communication components.
查看更多>>摘要：Constructing core-shell heterostructures can effectively improve the hindered issues such as decreased sensitivity and poor selectivity from the chemoresistive gas sensors in the complex atmosphere. Herein, an effective hydrothermal-water bath treatment combined strategy was designed to obtain the unique ethanol adsorption preferred ZnIn_2S_4 sheet shell/In_2O_3 sphere core (ZnIn_2S_4 @In_2O_3) nanosphere (NS) heterostructures. Particularly, according to the characterization and gas sensing test results, the chemoresistive sensor of ZnIn_2S_4 @In_2O_3 NS-2 with the highest chemisorbed oxygen concentration shows satisfactory selectivity to ethanol vapor, and the response is the highest (54) compared to other composite controls, which is almost 4-fold of that of the pure In_2O_3 NS reference. Besides, the relatively lower working temperature (220 °C), low limit of detection (LOD, 30 ppb) and long-term stability were also obtained. The enhanced performance of the core-shell ZnIn_2S_4 @In_2O_3 NS-2 based sensor may be due to the synergistic effect between ZnIn_2S_4 sheets and In_2O_3 sphere moieties. Meanwhile, the large specific surface area from the outer shell of ZnIn_2S_4 sheets is also another contribution factor, which supplies the most chemisorbed oxygen sites and transportation channels to promote the interfacial gas diffusion, catalytic oxidation and product desorption.
查看更多>>摘要：Laser powder bed fusion (LPBF) is a robust metal additive manufacturing technology which can produce precise parts with high complexity and freedom. In a recent work by the authors, a significant number of microstructural defects was observed on the surface of the LPBF-fabricated parts, which could account for the poor tensile strength of the parts. It was revealed that the regions near the surface of the part are more affected by the convection heat transfer mode compared to the areas located away from the surface. In this study, for the first time, a novel technique is proposed to address the issue of microstructure inconsistency in the LPBF-fabricated Inconel 718 parts. This approach is based on the design and fabrication of a border surrounding the main part during the LPBF fabrication. It is hypothesized that such a border, if designed appropriately, would mitigate the undesirable convention heat transfer mode in the areas near the surface of the LPBF-fabricated parts and may result in microstructure homogeneity. To this aim, cubic samples surrounded by borders at two different gap distances of 0.5 mm and 2 mm were fabricated to control the rate of heat dissipation and thus control the microstructure along the cross section and reduce surface defects such as microcracks and porosities. Reference cubic samples were fabricated without borders to compare them with the samples fabricated with borders. Scanning electron microscope (SEM) and optical microscope were used to study the changes in microstructure, X-ray diffraction (XRD) was used to perform compositional analysis, and Vickers hardness test was conducted to study the hardness properties. For the sample fabricated with a smaller gap, the smaller melt pools overlapped to form deeper melt pools and led to the formation of more columnar grain structures elongated parallel to the build direction. The fabrication of borders around the sample also helped in controlling the heat transfer of the sample and thus reducing the surface porosities and defects. A higher level of secondary strengthening phases (γ, γ") was seen to precipitate into the matrix for the samples fabricated with borders. Vickers hardness values were higher for the samples fabricated with borders than that of the reference sample.
查看更多>>摘要：For applications involving sodium-ion capacitor (SIC) with high energy and high power, it is necessary to develop cathode materials with high operating voltage, high capacity, and excellent cyclic stability. Prussian blue and its analogs are considered promising candidates for cathode materials owing to their high energy and high stability resulting from their open framework structure. We demonstrate that the Prussian blue-graphene oxide composite (PBGO) can be applied to SIC as a battery-type cathode. PBGO is synthesized by a single-step decomposition method and has a morphology in which graphene oxide covered Prussian blue, which has a uniform cubic structure. PBGO exhibit a high capacity of 165 mAh g~(-1) at 20 mA g~(-1), as well as 68 mAh g~(-1) at a high current density of 4 A g~(-1). The SIC is fabricated using PBGO as the cathode materials and activated carbon (AC) as a capacitor-type anode, and it exhibit a high specific energy density of 65.3 Wh kg~(-1) and a superior capacity retention of 78.8% after 10,000 cycles. The use of battery-type cathodes presents a promising strategy for developing SIC with high energy and long lifespan.
查看更多>>摘要：LiFePO_4/C (LFP/C)-coated LiNi_(0.8)Co_(0.1)Mn_(0.1)(NCM811) was prepared by a simple ball milling method (400 rpm for 4 h), and the influence of different coating amounts of LFP/C on the electrochemical performance of NCM811 was studied in detail. When the LFP/C coating amount was 1 wt%, the material maintained good electrochemical cycling stability and rate performance. The capacity retention of NCM811 @ 1 LFP/C after 300 cycles was 61.6% at 25 °C, which was significantly better than the corresponding value of 48.63% of NCM811. Simultaneously, the high temperature (55 °C) and high pressure (2.8-4.5 V) cycling stability performance of NCM811 @ 1 LFP/C was also better than for uncoated materials. The EIS results showed that the 1 LFP/C modification effectively reduced R_(SEI) (from 46.37 to 32.13 Ω) and Rct (from 155.9 to 113.5 Ω), which was beneficial for the interface charge transfer of electrons and Li~+ ions, consistent with the CV analysis. The XRD, XPS, and FESEM results indicated that the coating layer suppressed the changes in the NCM811 particle macro-volume and reduced the side reactions, improving the electrochemical performance of Nickel-rich layered materials.
查看更多>>摘要：The adjustment of the antiferroelectricity of a perovskite cell and the reversibility of antiferroelectric (AFE) -ferroelectric (FE) phase transition under electric field is very important for achieving excellent energy storage properties in AFEs. In this work, obvious change of antiferroelectricity was found in novel Na(Nb_(1-x)Sb_x)O_3 lead-free ceramics fabricated via a conventional solid-state reaction method. Repeatable double P-E loops with large E_(A-F) -28 kV/mm and large E_(F.A) -10 kV/mm were obtained in the x = 0.1 ceramic with AFE P phase at room temperature, resulting in excellent energy storage properties with W_(rec) -3.4 J/cm~3, large C_D -366 A/cm~2, high P_D -26 MW/cm3 as well as fast discharge rate t_(0.9) -75 ns. The multiscale structure analysis results indicate that the increased antiferrodistortive (oxygen octahedral tilting) degree and the decreased off-centering displacements of B-site cations after the substitution of Sb for Nb make the main contributions to the achievement of stable AFE phase and reversible AFE-FE phase transition in this work. The Na(Nb_(1-x)Sb_x)O_3 ceramics with excellent energy storage properties show large potential for the next-generation pulse power capacitor applications, and the mechanism for modulating antiferroelectricity found in this work would provide guidance for designing high-performance AFEs.
查看更多>>摘要：Interfacing two-dimensional materials with three-dimensional world is never a subject that could be bypassed. In this work, MoS_2 nanoflakes were purposefully stacked to construct hollow tetrapod structure, which showed great development prospects as a powerful anode material in potassium-ion-battery realm. The accumulation of these tetrapods could build a grand macroscopic interconnected architecture with high porosity, which was propitious to penetration of electrolyte, accessibility of K~+ ions and reduction of K~+-ion diffusion distance. Moreover, it could provide adequate room for volume changes during potassiation/de-potassiation, and the lattice stress applied on one arm upon cycling could readily transfer to another arm, leading to high structural stability. More than that, the wedge-shaped arms securely anchored the carbon black, so as to make full contact between active material and conductive agent, and thus enhancing electrical conductivity of the whole anode. Furthermore, the hollow arms could also accelerate K~+-ion transport and cushion the volume variation to the greatest extent. This delicately-designed structure showed excellent cyclability, enhanced initial Coulombic efficiency and exceptional rate capability during electrochemical processes.
查看更多>>摘要：Investigating on the effect of sodium formate mediated double regulation in TiO_2 photocatalytic reduction of cadmium is firstly reported. Multiple characterized methods were used to characterize and confirmed the successful reduction of Cd~(2+) to the form of metal elements by sodium formate-P25 system. The metal elements were attached to the surface of the composite photocatalyst were directly observed by SEM. The removal efficiency of Cd~(2+) for the composite photocatalyst was tested. When the addition of sodium formate was 1 g/L, the maximum removal rate of Cd~(2+) was 94.8% within 10 min. Further experiments showed the mechanism and activity of the combined catalysis of sodium formate and photocatalysis and the role of composite photocatalyst in photocatalytic activity. This is mainly due to the bidentate chelation between sodium formate and TiO_2 which makes it possible to adsorb heavy metal ions and the transfer of photo-generated electrons on the bidentate complex, which improves the survival time of the electrons and reduces the metal ions.
Tomas MurauskasVirgaudas KubiliusMartynas Talaikis
8页
查看更多>>摘要：La:BaSnO_3 has recently emerged as an outstanding perovskite oxide material due to its high electron mobility. To-date, lower electron mobility in thin films compared to the single-crystal are discussed in terms of the presence of dislocations, nearly neglecting the role of cation nonstoichiometry. However, by controlling Sn/Ba compositional ratio, we demonstrate the significance of stoichiometry and resulting point defects on microstructure, morphology, electrical properties, and Raman defect modes in epitaxial La:BaSnO_3 films. A narrow compositional window is demonstrated to yield high mobility and smooth morphology in La:BaSnO_3 thin films using the metalorganic chemical vapor deposition. The room temperature electron mobility of 121 cm~2V~(-1)s~(-1) and 85 cm~2V~(-1)s~(-1) was achieved on SrTiO_3 and MgO substrates, respectively. Correlation between the lowering of the A_1 g soft mode near 140 cm~(1) frequency and increase in the carrier mobility is demonstrated by Raman spectroscopy analysis. It was suggested that the position of this soft mode might be employed as a marker band for probing the electrical properties of La-doped BaSnO_3 perovskites.
查看更多>>摘要：As inspired by the surging demand for high performance energy storage systems, researchers have been designing and exploring advanced electrode materials exhibiting higher energy and power densities. In this study, a novel combination of nickel-cobalt sulfide and oxide was reported for high performance super-capacitors. The porous α-Ni(Co)S@NiCoO_2 composites with core-shell structure were derived from the well-designed precursor with Ni_2CoS_4 and ZIF-67 serving as the self-sacrificing templates through a two-step calcination process at elevated temperatures. Such a heterostructure exhibited an ultra-high specific capacity of 502.4 mA h g~(-1) at a current density of 1 A g~(-1), which was attributed to the unique porous core-shell structure and the ingenious combination of bimetallic sulfide and oxide. Furthermore, a hybrid supercapacitor based on the α-Ni(Co)S@NiCoO_2 composite and commercial activated carbon achieved a high energy density of 82.4 Wh kg~(-1) at a power density of 847.5 W kg~(-1). The prominent electrochemical performance exhibited by the α-Ni(Co)S@NiCoO_2 heterostructure in this study was demonstrated to be promising to practically serve as advanced electrode materials in supercapacitors.
NSTL
Elsevier