查看更多>>摘要：As-explosive welded clad plates usually show poor ductility due to heavily deformed microstructures developed after explosive welding (EXW). In this study, the feasibility of improving mechanical properties of an EXWed Mg-6Al-1Zn-lCa (AZX611)/AI-0.6Mg-0.6Si-0.1Fe (A6005C) (all in wt%) clad plate has been explored by subsequent hot-rolling. Increasing the thickness reduction per pass from 10% to 28% or decreasing the rolling temperature from 430 °C to 250 °C is shown to enhance tensile properties. The joint sheet rolled at 250 °C with a thickness reduction per pass of 28% shows a large fracture elongation of 15%, which is significantly higher than that of the as-EXWed clad plate, 1.2%. Microstructure characterization by means of scanning electron microscope, electron backscatter diffraction and transmission electron microscope reveals that the substantial improvement in ductility is intimately related to a significant reduction of the accumulated strain in AZX611 and A6005C alloy sheets and an elimination of the interface delamination formed during EXW. A certain degree of anisotropic mechanical properties is observed in all sheets regardless of rolling conditions, which can be ascribed to the mechanical anisotropy originated from the AZX611 and A6005C alloy sheets.
查看更多>>摘要：The high-entropy effect suggests the possibility of unusual thermal transport properties that may be favorable for thermoelectrics. Novel perovskite-type high-entropy (Ca_(0.25)Sr_(0.25)Ba_(0.25)La_(0.25))TiO_3 (4La) and (Ca_(0.25)Sr_(0.25)Ba_(0.25)Ce_(0.25))TiO_3 (4Ce) ceramics were successfully prepared through a conventional solid-state reaction method. XRD, SEM-EDS, and HRTEM were performed to confirm that the chosen multi-component cations can be introduced into A-site to form a single cubic phase with Pm-3m space group. Introduce high-entropy engineering, constituent elements competing inter into the A-site creating lattice distortion and strain fields, which results in extensive structural defects including dislocations which contributed to the phonons scattering of mid wavelength. Grain boundaries and intrinsic oxygen vacancies respectively scatter phonons of high and low wavelengths. The enhanced effective scattering of phonons through the multi-scale defects gives rise to a low lattice thermal conductivity of 2.5 W-m~(-1)-K~(-1) at 1073 K for the 4La ceramics, much lower than that of SrTiO_3-based perovskite thermoelectric ceramics. The high-entropy 4La ceramics possess the maximum power factor of 420 μW-m~(-1)K~(-2). This work provides a strategy of compositional design for thermoelectric oxides with decreased intrinsic thermal conductivity for thermoelectric applications.
查看更多>>摘要：We present the results of thermodynamic and optical spectroscopy measurements of the Pr_3CrGe_3Be_2O_(14) compound - a member of the recently discovered Be-subgroup of the langasite family. Despite the presence of both rare-earth and transition-metal subsystems in Pr_3CrGe_3Be_2O_(14), no long-range magnetic order has been found down to 0.4 K in terms of both magnetization M and specific heat C_p. These data are compared with those on Pr_3AlGe_3Be_2O_(14). Both compounds evidence the Schottky anomaly at low temperatures, most pronounced in the case of Pr_3CrGe_3Be_2O_(14).
查看更多>>摘要：The synergistic integration of compositional and structural advantages for anode material provides a feasible avenue toward high-performance lithium-ion batteries (LIBs). Here, a tailored Co/N-doped yolk-shell porous carbon skeleton is fabricated by graphitic carbon nanochambers and amorphous carbon to effectively enhance the electrochemical performances of LIBs. Benefitting from the exquisite composition and structure, the designed anode material delivers a desirable discharge capacity of 440.3 mA h g~(-1) after 2500 cycles at a current density of 4 A g~(-1) with the Coulombic efficiency of 99.5%. The assembled lithium full battery with LiFePO_4 cathode achieves 288 Wh kg~(-1) after 200 cycles. The present strategy expands the direction of advanced material preparations for long-lifespan battery applications.
查看更多>>摘要：There is an imperative need for a single photodetector that can be used to detect the entire electromagnetic spectrum from the ultraviolet (UV) to the near-infrared (NIR). Such a device can reduce the cost and surface area required for device integration. In addition to broadband photodetection, optical transparency must be considered as another critical parameter. Poor transparency or opacity renders their use a deprecated choice in transparent electronics. In this paper, a completely transparent, electrode-free n-n heterojunction (n-ZnO/n-V_2O_5) photodetector is developed for high responsivity and microsecond responses. This is the least-studied type of heterojunction. It is a Schottky junction and can provide rapid device performance due to its unipolar carrier transport. The wide bandgap of ZnO and the narrow bandgap of V_2O_5 make this heterojunction a transparent broadband photodetector. The n-ZnO/n-V_2O_5 photodetector offers > 50% optical transmittance in the Vis-NIR region, with remarkably high photoresponsivities of 18.86 A/W, 6.10 A/W, and 4.40 A/W in the UV, Vis, and NIR regions, respectively. The device also offers high detectivity, high external quantum efficiency, and fast rise and fall times of 230 and 340 us, respectively. Briefly, this work provides a path towards the development of transparent, electrode-free broadband photodetectors for next-generation transparent electronics.
查看更多>>摘要：Secondary hot-working on dual phase titanium alloys are essential for microstructural modification to tailor mechanical properties, which is typically challenging due to a narrow available processing window, especially during industrial scale manufacturing. Poor workability, strain induced porosity and adiabatic temperature rise in α+β phase region (i.e., sub-transus) are some of the main challenges faced. Cyclic thermal treatment (CTT) is an emerging technology showing potentials for microstructure modification (i.e., globularisation) in Ti-6A1-4V with significantly reduced mechanical work in the α+β region. This study summarises the results of CTT investigations conducted on a wrought Ti-6A1-4V alloy subjected to various thermo-mechanical conditions to develop different initial microstructures. Samples with uniform strain distributions were extracted from pre-forged samples and subsequently subjected to CTT using both conventional electric furnace (i.e., for slow heating and cooling rates), and induction heating (i.e., for faster heating and cooling rates). CTT of the samples forged at sub-transus temperature in conventional furnace led to maximum (i.e. -100%) globularisation and significant coarsening of a grains, resulting in an equiaxed bimodal microstructure. On the other hand, CTT with induction heating method has resulted in a maximum of 80% globularisation fraction in samples forged to 60% reduction, and -35% globularisation fraction in those forged to 20% reduction. The globularisation mechanisms during CTT of the sub-transus forged samples was dominated by the boundary splitting and thermal grooving. A Johnson-Mehl-Avarmi-Kolmogorov (JMAK) based model has been developed to predict the evolution of globularisation and grain growth during CTT. The developed JMAK model was then successfully incorporated into DEFORM~R software as post-processing user subroutines. The predicted microstructure evolution by Finite Element (FE) simulations shown a good convergence towards the experimentally measured data following CTT.
查看更多>>摘要：A photostable Ag_3PO_4/BCN type-II p-n heterojunction has been demonstrated by loading nano Ag_3PO_4 on B-doped g-C_3N_4 nanosheet (BCN). The photocatalysts were successfully characterized by various physico-chemical techniques and their photocatalytic activities were tested towards the water oxidation reaction to produce oxygen and Cr (VI) reduction under visible light. The HRTEM confirms Ag_3PO_4 with a particle size of 15 nm has been deposited on BCN to construct a p-n heterojunction. The BCNS-50 absorbs more visible light in the solar spectrum as compared to other catalyst, demonstrating the ability to generate 587 umol h~(-1)g~(-1) O_2 and reduces 98% of 20 ppm Cr (VI) solution in 1 h. The lower PL intensity as well as lower arc value in case of BCNS-50 suggests the maximum e-h separation and lower charge transfer resistance across the semiconductor/electrolyte interface. The BCN sheet provides a compact heterojunction where the oxidation peak of Ag_3PO_4 decreases gradually and disappear in case of BCNS-50 suggesting the enhance stability of Ag_3PO_4 in the heterojunction. BCNS-50 could able to produce -139 and 3087.5 uA photocurrent both in cathodic and anodic direction which is approximately 7 and 2.4 folds higher as compared to nano Ag_3PO_4. The generation of photocurrent in both cathodic and anodic direction confirms the formation of p-n heterojunction which further supported by Mott-Schottky analysis. Furthermore the construction of the p-n heterojunction is verified via Mott-Schottky study. DFT calculation explains the contribution of various atomic orbital of Ag_3PO_4 and BCN towards the formation of hybrid orbital in the heterojunction and the path for charge derealization between them. This work may provide a limelight and alternative pathway for enhanced photocatalytic performance on construction of the p-n heterojunction in a simple way.
查看更多>>摘要：Trimethylamine (TMA), which mainly emanates from decaying fish, is an important freshness indicator of seafood. In this work, a TiO_2-NiFe_2O_4 heterojunction was successfully synthesized for TMA detection using a simple and efficient hydrothermal method. The materials were characterized using X-ray diffraction, scanning electron microscopy, photoluminescence spectroscopy, and ultraviolet-visible diffuse reflectance spectroscopy. The TiO_2-NiFe_2O_4-based sensor exhibited the largest response (12) to 10 ppm of TMA at 307 °C The response was further improved under white-light irradiation, increasing from 2.5 to 4.5 as the TMA concentration approached 3 ppm. The enhanced gas-sensing performance of the TiO_2-NiFe_2O_4 sensor under light irradiation was then explored by density functional theory (DFT) with an optical carrier. We believe that the developed strategy improves the gas-sensing ability for TMA detection and can potentially be used in gas sensors.
查看更多>>摘要：Additive manufacturing has been vastly applied to fabricate various structures of nickel-titanium (NiTi) shape memory alloys due to its flexibility to create complex structures with minimal defects. However, the microstructure heterogeneity and secondary phase formation are two main problems that impede the further application of NiTi alloys. Although post-heat treatment is usually adopted to improve or manipulate NiTi alloy properties, it cannot realize the spatial control of thermal and/or mechanical properties of NiTi alloys. To overcome the limitations of uniform post-heat treatment, this study proposes an in-situ heat treatment strategy that is integrated into the directed energy deposition of NiTi alloys. The proposed method will potentially lead to new manufacturing capabilities to achieve location-dependent performance or property manipulation. The influences of in-situ heat treatment on the thermal and mechanical properties of printed NiTi structures were investigated. The investigations were carried out in terms of thermal cycling, microstructure evolution, and mechanical properties by 3D finite element simulations and experimental characterizations. A low-power laser beam was adopted to localize the in-situ heat treatment only to the current printed layer, facilitating a reverse peritectic reaction and a transient high solution treatment successively. The proposed in-situ heat treatment on the specimen results in a more obvious phase transformation peak in the differential scanning calorimetry curves, about 50-70% volume reduction for the Ti_2Ni phase, and approximately 35 HV reduction on microhardness.
查看更多>>摘要：From the XRD results, it is found that the studied La_(0.5)Ca_(0.2)Ag_(0.3)MnO_3 compound crystallizes in the or-thorhombic structure with Pnma space group. Electrical conductivity of La_(0.5)Ca_(0.2)Ag_(0.3)MnO_3 compound is investigated from 80 K to 480 K in the frequency range [40 Hz-6 × 10~5 Hz]. Several conduction models are used to identify the appropriate mechanisms governing the transport properties in the studied compound. The Overlapping-Large- Polaron Tunneling and the Correlated Barrier Hopping conduction processes are used to clarify the sub-linear dispersive regions in the DJPL/JPL frequency range. In these regions, the conductivity is examined according to double and single Jonscher power laws. At lower temperatures and for the second frequency range, the spectra reveal Superlinear Power-Law behavior. Beyond T = 280 K, this phenomenon is disappeared and replaced by Nearly Constant Loss behavior. At higher frequencies, the conductivity spectra exhibit a high frequency plateau. For the DC regime, the transport properties are governed by thermally activated Small Polaron Hopping conduction process at elevated temperatures. The Variable Range Hopping conduction mechanism is the dominant process in the intermediate temperature range. Thus, the cationic disorder plays a major role in the transport of charge carriers at low temperatures. Likewise, the investigated compound exhibits semi-conductor behavior over the explored temperature region. The deduced hopping energy is sensitive to the frequency parameter. At high frequencies, a signature of a metal-semiconductor transition is observed at 260 K. The magnetic investigation shows that the sample reveals a paramagnetic-ferromagnetic phase transition at 260 K.
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Elsevier