查看更多>>摘要：? 2022 Elsevier B.V.In the current report, Silver doped Zinc Cobaltite (AgZnCo2O4, AgZCO) nanoparticles have been synthesized through a solvent-free strategy. Synthesized AgZCO nanoparticles were integrated with the reduced graphene oxide (rGO) sheets to prepare the AgZCO@rGO composite. Structural and morphological properties of ZCO, AgZCO, and AgZCO@rGO were studied by various physio-chemical techniques. X-rays diffraction (XRD) analysis showed that all prepared samples possess face-centered cubic crystal structures with crystallite sizes of 5.79 nm, 5.27 nm, and 5.16 nm for ZCO, AgZCO, and AgZCO@rGO, respectively. Scanning electron microscope (SEM) analysis displayed that small spherical nanoparticles of AgZCO were wrapped inside rGO, along with some of the particles present on the surface of rGO sheets. FT-IR characterization showed the presence of all necessary vibrational modes. The results of the photocatalytic experiment showed that 41.97%, 58.02%, and 75.30% MB dye was degraded by the ZCO, AgZCO, and AgZCO@rGO respectively. 65.06% methyl orange dye was degraded by the AgZCO@rGO and it showed the highest percentage degradation with a higher kinetic rate than ZCO and AgZCO catalysts.
查看更多>>摘要：? 2022Inconel 718 alloy fabricated by selective laser melting (SLM) was used to investigate the evolution of precipitated phase from as-SLM to heat-treated (HT) samples. A heat treatment, including homogenization, solution and aging heat treatments, was proposed to obtain SLMed Inconel 718 alloy components for desirable mechanical performance. Post heat treatment process can reduce the number of original print defects due to grain boundary migration and grain growth. The solid solution plus double aging treatment (HT-1) results in the precipitation of large amounts of δ phase within the grain and at grain boundaries, as well as a small amount of massive MC. Homogenization, solid solution plus double aging (HT-2) eliminated a large amount of internal δ phases in the grain as well as needle-like δ phases at grain boundaries. However, the single aging (HT-3) still retains some of the needle-like δ phase. Heat-treated specimens increased tensile strength by 20–24% at room temperature and maintained high strength at 650 °C compared to the as-SLM. Further fatigue results also confirmed that the HT-2 treatment increases the fatigue life by an order of magnitude compared to the as-SLM to 108 cycles at a stress amplitude of 300 MPa. This work is anticipated to provide a potential route to obtaining attractive mechanical properties for SLM superalloy components.
查看更多>>摘要：? 2022 Elsevier B.V.The effects of pre-stretching prior to natural aging on the behavior of dislocation evolution, the precipitation behavior, microstructure and mechanical properties of an in-situ TiB2/2024 Al composite were investigated. Pre-stretching introduced a strong increment in the dislocation density, and meanwhile facilitated uniform distribution of dislocations. The dislocation structure evolved from parallel dislocation lines to dislocation cells, and finally formed uniform dislocation networks. The heterogeneous nucleation of the S’’ precipitates occurred on the more uniform-distributed dislocations. Finer and more evenly distributed S’’ precipitates were achieved. Based on these refined microstructure features, the mechanical properties of TiB2/2024 Al composite presented a significant increase in yield strength and tensile strength, from 306 ± 6 MPa and 508 ± 3 MPa without pre-stretching to 504 ± 3 MPa and 542 ± 5 MPa for the composite subjected to 8% nominal strain pre-stretching, respectively. Meanwhile, a loss of plasticity took place on the pre-stretching composites. The results in this work provided important insight into tuning the thermo-mechanical treatment which possesses improved mechanical properties.
查看更多>>摘要：? 2022 Elsevier B.V.Threshold switching devices with Ag-doped amorphous chalcogenides show enhanced threshold switching characteristics of a high selectivity and a low current in the subthreshold region. However, the mechanism underlying the decrease in this subthreshold current caused by Ag doping is not well understood. In this study, the effects of Ag doping in amorphous Ga2Te3 are investigated in terms of the change in bonding structure and localized states in conjunction with threshold switching characteristics. X-ray photoelectron and Raman spectroscopies reveal the formation of Ag–Te bonds with a reduction in the amount of Te–Te bonds in Ga2Te3. In addition, the UV absorption shows an increase in the optical bandgap and a decrease of Urbach energy with Ag doping. The subthreshold current of the Ag-doped Ga2Te3 device decreases by a factor of seven, and accordingly, the selectivity increases with respect to that of the undoped device. In addition, analyzing on the subthreshold conduction with a thermally assisted hopping model demonstrates a decrease in the density of localized states. Thus, the enhanced threshold switching characteristics of Ag-doped Ga2Te3 are associated with the reduction of Te-induced localized states and the formation of Ag–Te bonds.
查看更多>>摘要：? 2022We report the findings of an experimental and theoretical analysis of the structural, electronic, and vibrational characteristics of Ba2GdRuO6 and Sr2GdRuO6 double perovskite ruthenates. The samples of Ba2GdRuO6 and Sr2GdRuO6 were synthesized using solid state reaction method. The samples have been characterized by X-ray diffraction (XRD) technique where phase purity and space group information have been obtained using FullProf Rietveld refinement method. The Rietveld-fitted XRD patterns show that Ba2GdRuO6 has a single-phase cubic structure with space group Fm3ˉm and that Sr2GdRuO6 has a monoclinic structure with space group P21∕n. The vibrational properties were measured, via., Raman spectroscopy performed at room temperature. The structures predicted from XRD were studied theoretical using accurate plane wave pseudo-potential method based on density functional theory (DFT) with Hubbard parameter, U (DFT+U). The Ba2GdRuO6 is found to be metallic with difference in density of states for spin up and spin down electrons; whereas Sr2GdRuO6 is insulating with a band gap of 4.0 eV. The vibrational analysis of pervoskites shows A1g, Eg and 2F2g, Raman active modes for Ba2GdRuO6; while for Sr2GdRuO6 the observed active modes were Ag and Bg, respectively. It's worth noting that the experimentally measured values match those predicted by our DFT calculations.
查看更多>>摘要：? 2022 Elsevier B.V.We investigate the effect of europium doping on the optical properties and electrical conductivity of hydrothermally grown ZnO nanorods. The widening of optical bandgap with europium doping occurs because of the Burstein-Moss effect upto 0.8% and bandgap renormalization is observed at higher concentration. The temperature-dependent resistivity measurements of the individual nanorods reveal that the intrinsic electrical conductivity is a combination of thermally activated and nearest-neighbor hopping conduction processes at high and low-temperature regimes, respectively. We can successfully correlate that the modulation of carrier concentration in the defect D and D? bands can tune both bandgap and electron transport in Eu doped ZnO nanorods.
查看更多>>摘要：? 2022 The Author(s)Temperature sensing by using near-infrared (λ = 976 nm)-excited upconversion (UC) of Yb, Er and Tm co-doped orthorhombic β’Gd2(MoO4)3 combines remarkable good sensitivity and thermal resolution from room temperature to 890 K, thanks to the use of three different ratiometric luminescence probes. Two of them are based on pairs of thermally coupled levels, namely 2H11/2→4I15/2 vs 4S3/2→4I15/2 Er3+ green emissions (R1) and deep-red 3F3→3H6 vs NIR 3H4→3H6 Tm3+ emissions (R3). The third one uses non-thermally coupled levels, blue 1G4→3H6 vs deep-red 3F3→3H6 Tm3+ emissions (R2). This multiprobe approach allows the optimization of the thermometric parameters for each selected temperature range. Based on absolute thermal sensitivity (SABS), R1 is the best option for sensing from room temperature up to about 442 K, with R1 SABS = 103 × 10?4 K?1 and excellent thermal resolution δT< 0.04 K at 300 K, while at higher temperatures, R2 is the most adequate probe since it combines an extraordinary increase of R2 SABS up to 20300 × 10?4 K?1 at 776 K and very good δT< 0.2 K. When the relative thermal sensitivity (SREL) evaluation is required, R3 is the probe of choice from room temperature up to 522 K, offering simultaneously the highest R3 SREL = 3.3% K?1 and δT = 0.07 K at 300 K, with a minimum δT = 0.05 K achieved at 522 K, but R2 is still the most convenient probe for high temperature sensing, with R2 SREL = 1.6% K?1 and δT = 0.25 K. Therefore, doping β’Gd2(MoO4)3 simultaneously with Er3+ and Tm3+ provides a unique way to span the sensing temperature up to 890 K while maintaining suitable high thermal sensitivity and thermal resolution along the whole temperature range. Several favourable UC aspects specific of β’Gd2(MoO4)3 are identified as being responsible for advantages over its βNaYF4 counterpart for high temperature sensing.
查看更多>>摘要：? 2022 Elsevier B.V.Transparent polycrystalline ceramics doped with active ions are suitable for many potential optical applications. Fabrication methods that utilize applied external pressure show promise as they allow reducing sintering temperatures and produce transparent non-cubic ceramics. However, not much attention has been given to the dissolution of doping elements while sintering under relatively high pressure and low temperature conditions. In this study, we employed high-pressure spark plasma sintering (HPSPS) for fabrication of Cr:Al2O3 ceramics and investigated the effect of two different synthesis routes on densification and optical properties. Namely, HPSPS of Cr-doped alumina powders prepared by directly doping with 0.05, 0.2, and 0.5 Cr at.% via co-precipitation and alumina mixed with similar mol.% of Cr2O3 nanoparticles towards doping via solid-state reactive sintering (so-called ‘synthesized’ and ‘mixed’, respectively). Remarkable differences in optical properties between samples obtained by each method were observed. The ceramics fabricated from synthesized powders exhibited pink shades of ruby, high transparency, and strong photoluminescence. In contrast, the mixed ceramics exhibited green color, low transparency, and weak photoluminescence. It was found that in the green samples, most of the Cr2O3 nanoparticles remain as undissolved nano-inclusions. These inclusions are detrimental to optical properties and cause green pigmentation of the alumina. Post-sintering heat treatment dissolved the inclusions and the added Cr3+ in alumina increased photoluminescence. Evidently, doping transparent alumina via reactive sintering is not viable for processes such as HPSPS. Nevertheless, rapid low temperature densification might enable the design of functional translucent ceramics with integrated second phase nanoparticles.
查看更多>>摘要：? 2022 Elsevier B.V.Designing bimetallic sulfide materials with well-defined nanostructure and high energy density is indeed desirable for high-performance supercapacitors. Here, a hollow zinc cobalt sulfide (ZnxCo3?xS4) dodecahedron with plentiful sulfur vacancies is synthesized through a co-precipitation approach followed by a solvothermal vulcanization treatment. The tailored hollow structure can effectively accelerate the charge transport and facilitate the diffusion of OH-, whereas the sulfur vacancies significantly increase the amount of contact active sites and enhance the electronic conductivity. Both of the features can simultaneously promote the capacitance performance of ZnxCo3?xS4 for supercapacitors, where the most-performing Zn0.3Co2.7S4 electrode, achieves a high specific capacitance of 545.9 C g?1 in 3 M KOH electrolyte at the current density of 1 A g?1 and excellent long-term durability of 84.7% capacity retention after 1000 cycles. Particularly, the assembled aqueous hybrid supercapacitors delivers high energy density and superior cyclic stability. This study demonstrates a rational design of well-controlled bimetallic sulfides with outstanding electrochemical performance for energy storage devices.
查看更多>>摘要：? 2022The SF6 gas in gas-insulated switchgear (GIS) systems decomposes into SO2F2, SOF2, SO2, and H2S under abnormal conditions such as partial discharge. The detection of these decomposition gases with high sensitivity is essential for the safe operation of GIS devices. Herein, we report the synthesis of cerium oxide and multiwalled carbon nanotube composite (CeO2@MWCNTs). The CeO2@MWCNTs composite was characterized by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and Brunauer–Emmett–Teller analysis. The CeO2@MWCNTs composite sensor provided a response value of 7.7 at 100 ppm of SO2F2 at a low operating temperature (50 °C), and the response and recovery features of the CeO2@MWCNTs composite sensor were recorded at 43 and 28 s, respectively. Moreover, the composite sensor exhibited excellent stability after two months. The developed CeO2@MWCNTs composite sensor can offer an exceptional platform for gas sensing applications in diverse fields.
NSTL
Elsevier