查看更多>>摘要：? 2022 Elsevier B.V.The x-type hexaferrites have been getting considerable attention owing to their promising application in electronic fields. Though, the growth of nanosized crystal X-type hexagonal ferrites is still a big challenge. Herein, the synthesis of nanosized X-type hexagonal ferrites Ca2Co2?xZnxFe28O46 (X = 0.0, 0.4, 0.8, 1.2, 1.6, and 2.0) with high quality is reported using the auto-combustion sol-gel method. The objective of the study was to improve the structural and dielectric properties of X-type hexagonal ferrite which was achieved through variation of concentration of cobalt and zinc. Structural, morphological, and dielectric properties were investigated. X-ray diffraction (XRD) patterns confirmed the single-phase x-type hexagonal structure. The crystal size of all samples was in the range of 22.7–23.8 nm. Other parameters such as D-spacing, lattice parameters, unit cell volume, dislocation density, atomic packing fraction, degree of crystal lattice distortion, number of the unit cells, and volume of particles were also calculated. Fourier transform infrared spectroscopy (FTIR) confirmed the formation of metal oxide bonds with two absorption bands at 574 cm?1 and 424 cm?1. The morphology of the prepared Ca2Co2?xZnxFe28O46 with the variation of Co and Zn was examined by scanning electron microscopy. Increasing crystallinity and agglomeration were observed with the upsurge in Zn and Co. The dielectric properties of Ca2Co2?xZnxFe28O46 with the variation of Zn and Co revealed that these materials might be considered good candidates for modern devices.
查看更多>>摘要：? 2022 Elsevier B.V.Transition metal oxides have obtained considerable research attention in energy storage devices. In this study, we demonstrate the preparation of hierarchical CoMn2O4 @Ni(OH)2 nanowire arrays (CoMn2O4 @Ni(OH)2/Ni) by a combination of hydrothermal reactions and annealing process. This hybrid CoMn2O4 @Ni(OH)2/Ni electrode possesses a significantly enhanced capacity of 8.5 F cm?2 at 1 mA cm?2 (3017.9 F g?1 at 0.4 A g?1). Additionally, the assembled all-solid-state asymmetric supercapacitor (CoMn2O4 @Ni(OH)2/Ni//AC ASC) displays a comparable energy density of 76.2 Wh kg?1. Meanwhile, the prepared CoMn2O4 @Ni(OH)2/Ni anode revealed initial discharge capacity (~3548.2 mAh g?1). After 50 cycles, the CoMn2O4 @Ni(OH)2/Ni anode also shows a satisfied cycling stability (1437.4 mAh g?1 of capacity maintained). Further, the LED devices can be lit up for more 230 min by the assembled CoMn2O4 @Ni(OH)2/Ni cell. Therefore, this novel CoMn2O4 @Ni(OH)2/Ni materials with excellent electrochemical property have great potential in the high energy storage applications.
查看更多>>摘要：? 2022 Elsevier B.V.Exploring high-effect and pollution-free energy storage devices is the most important issue to be solved for many researchers. In this work, (Bi0.5Na0.5)TiO3-based lead-free ceramics were modified by La3+ in the A-site and (Al0.5Nb0.5)4+ in the B-site, respectively. In order to further modify, a linear dielectric of SrTiO3 was incorporated. By this means, novel (1-x)(Bi0.48La0.02Na0.5)Ti0.92 (Al0.5Nb0.5)0.08O3-xSrTiO3 [(1-x)(BLNANT)-xST] ceramics were prepared by traditional solid state reaction method. The crystal structure, microstructure, dielectric properties and energy storage properties were investigated. In particular, a great recoverable energy density (3.35 J/cm3) and efficiency (78.8%) were achieved under a low electric field of 255 kV/cm for the optimal composition. In addition, the P-E loops of this ceramic possess a good temperature (25–150 °C) and frequency stability (1–100 Hz) under the electric field of 150 kV/cm. Finally, an extremely fast discharge time (t0.9) of 71.3 ns and an eminent power density (PD) of 39.04 MW/cm3 can be obtained. These characteristics indicate that the ceramics of this work possess a good potential for high energy storage application.
查看更多>>摘要：? 2022 Elsevier B.V.The environment-friendly Cs2NaBiI6 double perovskite films have been fabricated using a one-step solution spin coating method in air. The X-ray diffraction analyzer, Ultraviolet-visible spectroscopy, scanning electron microscope, and X-ray photoelectron spectroscopy were carried out to characterize the films. The films were used to prepare the memory devices with the structure of Al/Cs2NaBiI6/ITO. The current?voltage characteristics of the devices clearly showed a bipolar resistive switching behavior. The estimated activation energy (~0.11 eV) proves that the conduction mechanism is mainly derived from the migration of iodine vacancies. Moreover, the devices showed the memory performances with an endurance up to 200 cycles, a higher ON/OFF ratio of over 102, a long retention time ~104 s, and outstanding reproducibility. Especially, the devices still keep excellent memory behaviors with the increase of measurement temperatures up to 403 K or after 90 days exposure in the air. The results indicate that the present double perovskite memory devices with a remarkable stability offer a great potential for future applications.
查看更多>>摘要：? 2022 Elsevier B.V.Construction of efficient and low-cost bifunctional electrocatalysts toward oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) for rechargeable Zn-air batteries is still a great challenge but highly desirable. Herein, a series of low-cost bifunctional electrocatalysts including Fe/C, Fe-NPCNs, FeCo-NPCNs, and FeCo-CNTs are prepared by simply carbonizing the mixture of Fe-based metal-organic frameworks (Fe-MIL-53), melamine, and CoCl2.6 H2O with different contents. Structure and electrocatalytic performance of the as-fabricated four samples are systematically investigated and the FeCo-NPCNs catalyst with a structure of FeCo nanoparticles uniformly embedded 3D porous N-doped carbon nanonetwork exhibits the highest electrochemical activity with a positive half-wave potential of 0.87 V vs. RHE for ORR and a low overpotential of 240 mV vs. RHE for OER with a ΔE of 0.60 V at 10 mA cm-2, together with excellent stability and methanol tolerance, even outperforming the noble-metal-based Pt/C-RuO2 catalysts. Besides, the results of density functional theory (DFT) calculations reveal the boosted intrinsic activity due to the reduced energy barrier both for ORR and OER. Furthermore, the assembled aqueous rechargeable Zn-air battery with FeCo-NPCNs catalyst manifests a large power density of 161.2 mW cm-2, a low charge-discharge gap of 0.78 V, and long-term ability. Likewise, the flexible solid-state Zn-air battery with FeCo-NPCNs catalyst also demonstrates high round-trip efficiency and excellent durability under various bending angles. This work may serve as a reference to designing advanced bifunctional electrocatalysts with 3D porous carbon nanonetworks for rechargeable Zn-air batteries.
查看更多>>摘要：? 2022 Elsevier B.V.Fabrication of lightweight, thin thickness, broad bandwidth, strong absorption, and lower filler loading materials are of great interest for microwave absorption. Herein, porous thermoplastic polyurethane (TPU) /graphene composites were successfully prepared via a facile vapor induced phase separation (VIPS) technique. Compared with TPU foam, the introduction of graphene endows the composites favorable microwave absorption ability. The optimized composite foam with 3 wt% graphene (TPU/G-3) exhibits extraordinary wave attenuation capacity with a minimum reflection loss (RLmin) value of ? 51.86 dB and effective absorption bandwidth (EAB) of 4.28 dB (12.6–17.0 GHz) at the thickness of 3.1 mm. Microwave attenuation mechanism indicates that the remarkable microwave absorption ability derives from conduction loss, dipole polarization loss, interfacial polarization loss as well as multiple scattering. Incorporating the same amount of Fe3O4 as graphene to TPU/G-3 endows the composites with the RLmin of ? 58.96 dB, which is slightly better than TPU/G-3 due to more favorable impedance matching. However, the matching thickness becomes much higher to about 8.0 mm, which is mainly attributed to bigger pores caused by Fe3O4. Moreover, the VIPS strategy provides insight into the fabrication of facile and lightweight polymer-based porous electromagnetic absorption materials.
查看更多>>摘要：? 2022 Elsevier B.V.The structures, crystal growth and preliminary NLO properties of a broad class of compounds known as the stuffed tridymites are investigated. The stuffed tridymites of the formula ABCO4, where A are the alkali metal ions and B and C are Group 13 and 14 metal ions, respectively, form an extensive series of structures, all of which are based on symmetry breaking of the parent tridymite (SiO2) structure. In all cases the alkali ion resides in channels running parallel to the c-axis formed from six-membered rings of tetrahedra of the metal ions. A large array of structures can be formed though combinations of ordering of the B/C sites, staggered and eclipsed tetrahedra, up/down orientations of the tetrahedra relative to the c-axis, and distortions of the six-membered rings. These symmetry breaking steps can be mixed and matched to form many different structures, and nearly all are in polar acentric space groups. The primary cause of centrosymmetric crystal formation is disorder of the B/C sites. When the sites are well ordered most of the structures are acentric with polar axes. High quality single crystals of most products can be grown using a high pressure hydrothermal method. Preliminary NLO experiments indicate that the compounds are acentric, but have low NLO conversions, which is expected due to the low polarizability of the building blocks. The extremely high percentage of polar acentric structure types, and the ability to correlate the structures to systematic variations of the very large and flexible tridymite structural class, suggests that this can serve as a starting point for designing crystals with many other useful physical properties.
查看更多>>摘要：? 2022 Elsevier B.V.A common feature of chalcogenide crystals is the presence of the chalcogen-chalcogen bonds, which result in very stable anion sub-structures (blocks) containing up to eight chalcogenide ions with the electric charge ? 2 in units of the proton charge like systems [PS4]3-, [SiS4]4-, [GeS4]4-, [GeSe5]4-, [Ge2Se6]6-. The size of anion blocks, their mutual arrangement and chemical bonds between them consequently determine the optical and detection properties. By modifying the chemical composition with subsequent use of the laser irradiation, it is possible to change crystal optoelectronic properties in a wide spectral range. In the work, we discuss the influence of the structural properties on the stability, electronic, optical and nonlinear-optical efficiency for the group of quaternary chalcogenide crystals with Ag(Pb)–Ga(In)–Si(Ge)–S(Se) composition, that have already found practical applications in IR optoelectronics and non-linear optics. The presented analysis of chemical composition-structure - nonlinear optical properties relationship can be useful for the creation of effective quaternary crystals for nonlinear optics application.
查看更多>>摘要：? 2022 Elsevier B.V.(CoNiCuZn)1?xMnxFe2O4 ferrite powders (x = 0.05, 0.1, 0.2, and 0.3) were easily prepared by the solution combustion method for absorption of electromagnetic microwaves. The effects of Mn contents on the structure, microstructure, and magnetic and microwave absorption properties were studied by various characterization methods. Single-phase spinel ferrites with a space group of Fd3?m were directly formed by the combustion method without further heat treatment. The lattice parameter increased with adding the Mn2+ ions, and the fraction of Fe3+ cations in (A) sites decreased because of the redistribution of various cations. The average size of spherical nanoparticles increased from 55 to 130 nm for x = 0.1 and decreased up to 70 nm for x = 0.3. The saturation magnetization first decreased from 69 to 54 Am2/kg for x = 0.2 and then increased to 70 Am2/kg for x = 0.3. The coercivity decreased from 17.9 to 11.6 kA/m with Mn2+ substitution. The (CoNiCuZn)0.95Mn0.05Fe2O4/paraffin composite sample exhibited the maximum reflection loss of ? 40 dB at Ku band (17 GHz) in the matching thickness of 5.3 mm. With the increase of Mn2+ content, the reflection loss decreased to ? 33 dB at the matching frequency of 4.2 GHz (C2 band). However, the (CoNiCuZn)0.7Mn0.3Fe2O4 sample had a wide effective bandwidth of 3.2 GHz at the matching thickness of 4.3 mm because of its good impedance matching caused by the proper combination of permittivity and permeability values.
查看更多>>摘要：? 2022 Elsevier B.V.This study focuses on the corrosion resistance of non-equiatomic Fe40Mn20Cr20Ni20 high entropy alloys (HEAs) with addition of various cerium (Ce) concentrations in 3.5 wt% NaCl solution. The results of potentiodynamic polarization tests demonstrated that cerium can improve the pitting resistance of the HEAs in a considerable manner. Notably, the critical pitting potential (Epit) of samples increased dramatically with the addition of cerium, from ? 58 mVSCE without cerium to + 265 mVSCE with 0.15 at% cerium in 3.5 wt% NaCl solution. Further the potentiodynamic polarization measures suggested that the impact of cerium addition on the pitting resistance of Fe40Mn20Cr20Ni20 HEAs is not sensible to the salt concentration. In addition, electrochemical impedance spectroscopy (EIS) and Mott-Schottky tests showed that the addition of rare earth cerium led to the increase of the passive film thickness and the reduction of the donor density in the passive film, which partly accounts for the observed enhanced pitting resistance of the HEAs.
NSTL
Elsevier