查看更多>>摘要：The basic aim of our study is to investigate the correlation between structural parameters and the electrocaloric effect in lead-free epitaxial Ba1?xSrxTiO3 (BSTO) based thin film architectures. Therefore, BSTO thin films with Sr contents of x = 0 to x = 0.3 were grown on SrRuO3 buffered SrTiO3 single crystalline substrates by pulsed laser deposition. Structural characterization verified an epitaxial growth for all Sr contents with an additional tetragonal distortion compared to bulk material. Temperature and frequency-dependent measurements of dielectric properties revealed increased permittivity values for thicker films with broad maxima indicating a diffuse phase transition. The temperature of maximum permittivity decreases with increasing Sr content, whereas polarization measurements indicate a relaxor-like behaviour in particular above room temperature. Adiabatic temperature changes were determined with the indirect method resulting in |ΔT| values of up to 2.9 K for a 680 nm thick BSTO layer with x = 0.3 at an applied electric field of 750 kV cm?1.
查看更多>>摘要：Phosphor covered light-emitting diodes (PC-LEDs) are wide applied to diverse fields due to its great advantages compared with the traditional light source. Therefrom, we report new rare-earth-free red-emitting Mn4+ doped Ca2InSbO6 and Sr2InSbO6 phosphors with excellent photoluminescence performance by the solid phase synthesis route. The resultant samples possess broad excitation band that is able to match well with current commercial near-ultraviolet (n-UV) chips and exhibit strong red emission at the excitation of n-UV light. Importantly, the quantum efficiency of the Mn4+-doped Sr2InSbO6 phosphor is measured to be 55.93%. Simultaneously, the quenching temperature of two phosphors is 403 and 438 K. Finally, the LED devices with strong white light are got and provided with low correlated color temperature (CCT) and good color-rendering index (CRI) values. And the emission spectrum overlaps with absorption curve of phytochrome protein Pfr. These results indicate the obtained sample can be a candidate for WLEDs and plant cultivation.
查看更多>>摘要：In this work, the influence of different heat treatments on the martensitic transformation and precipitation in polycrystalline Cu13%Al4%Ni shape memory alloys have been investigated. A CuAlNi strip were subjected to different heat treatments in order to obtain a variety of microstructures. In this way, the samples were aged at a temperature between 200 and 450 °C. Some specimens were heat-treated at 900 °C followed by ageing processes. The transformation temperatures were measured using Differential Scanning Calorimetry (DSC) method. To determine the mechanical properties, the samples were subjected to the tensile and hardness tests. Microstructural studies were performed using optical and scanning electron microscopies. According to the experimental results, increasing the ageing temperature up to 370 °C results in strength and transformation stress to increase. As the temperature rises to 350 °C, some precipitates appear in the microstructure. Once the temperature reaches 450 °C, there is no martensite in the microstructure. Accordingly, the hardness increases and the elongation decreases drastically in such a way that the alloy breaks in the elastic region. The solution treatment at 900 °C for 20 min yields the martensite to reappear in the microstructure resulting the hardness and strength to decrease and the elongation to increase. Ageing of the samples after solution treatment, increases the mechanical properties again but no precipitation takes place.
查看更多>>摘要：Aluminum matrix nanocomposites were manufactured by selective laser melting (SLM) of 0.5 wt% multi-walled carbon nanotubes (MWCNTs) modified Al-Mg-Sc-Zr alloys. The influence of MWCNT addition on the manufacturing quality, the phase formation and the mechanical properties of the Al-Mg-Sc-Zr alloys was investigated. It is found that primary Al3(Sc,Zr) particles precipitated and were uniformly dispersed in both equiaxed and columnar regions of the SLM-fabricated MWCNTs/Al-Mg-Sc-Zr nanocomposites. New Al4C3 phase was generated either on the open tip or in the defected and amorphous carbon layer of the MWCNTs, covering their overall surface. The unreacted MWCNTs completely transferred to Al4C3 upon heat treatment, forming a stable {003} Al4C3/{200}Al interface. The heat-treated MWCNTs/Al-Mg-Sc-Zr nanocomposites exhibit high microhardness of 169.0 ± 0.7 HV0.2, tensile strength of 544.2 ± 6.8 MPa, yield strength of 505.1 ± 6.3 MPa and elastic modulus of 97.8 ± 0.7 GPa, increasing by 6.3%, 4.5%, 5.0% and 5.6%, respectively, compared with the unmodified Al-Mg-Sc-Zr alloys. The improved performance was ascribed to the collective effects of precipitation strengthening of secondary Al3(Sc,Zr) nanoparticles, in-situ synthesis of Al4C3 as well as favorable interfacial bonding for effective load transfer. This study can provide reference values for laser additive manufacturing of MWCNTs modified other metallic alloys to enhance their comprehensive properties.
查看更多>>摘要：The hydrogen sorption properties of Ti4M2Oy compounds (M = Fe, Co, Ni, Cu or their mixture and y = 0, 1) were studied to assess their utility as room-temperature hydrogen storage materials. The main parameter controlling the hydrogen sorption property is the energy of hydrogen incorporation into the compounds, which was evaluated by density functional theory total-energy calculations. Energetics provides basic information on the sequence of hydrogen filling into the available interstitial sites, and when the minimum H–H distance is also considered, a more sensible prediction of the site occupation becomes possible. The calculation results suggested that between Ti4Fe2O and Ti4Ni2O, Ti4Ni2O was a better candidate for room-temperature hydrogen storage. An almost-single-phase Ti4Ni2O compound was successfully synthesized starting from TiO2, Ti, and Ni using the arc-melting method. Ti4Ni2O stored 1.3 wt% of hydrogen under 7 MPa of H2 pressure at 30 °C. The storage properties of Ti4Ni2O were modified by the partial substitution of Fe, Co, and Cu for Ni. The partial substitution did not improve the usable capacity, but the hydrogen absorption–desorption characteristics demonstrated that the equilibrium hydrogen pressure could be precisely controlled via composition change.
查看更多>>摘要：SnS has become a popular anode material for lithium-ion batteries (LIBs) because of its higher theoretical capacity and lower cost. However, the huge volume change and dissolution of sulfur lead to sharply attenuated capacity and less than ideal rate performance in the process of repeated discharge/charge. Here we use silica spheres and allyl thiourea as hard template and carbon/sulfur sources, respectively, to synthetize SnS nanoparticles anchored three-dimensional porous carbon (SnS/C nanocomposites) by in-situ carbonization and vulcanization method. As a result, the SnS/C nanocomposites exhibit high specific capacity (607.6 mA h g?1 at 0.1 A g?1), excellent rate performance (313.2 mA h g?1 at 3 A g?1), and outstanding cycling stability (404.7 mA h g?1 after 300 cycles at 1 A g?1). The distinguished electrochemical performance of SnS/C nanocomposites is due to the N, S-doped three-dimensional porous carbon interconnection structure and the wide range of SnS nanoparticles in the carbon matrix. Such combination not only improves the conductivity of the material but also maintains the integrity of the structure, eventually improving the cycling stability of the material.
查看更多>>摘要：In this work, the incorporation of porous reduced graphene oxide (RGO) as support for nickel cobaltite and its strong influence on a structural directing agent is studied. It was found in experimental results that the RGO nanosheets, especially the porous carbon network would be favorable to serve as the nucleation sites for the growth of NiCo2O4 nanorods. Importantly, the epoxy groups present in the porous RGO attract an aggregated NiCo2O4 nanoparticle to form aggregated nanorod-like morphology through dangling bonds. The specific capacity of the NiCo2O4/RGO hybrid (606.6 C g-1 at 1 A g-1) is two times superior than that of NiCo2O4 (282.6 C g-1) and the high-rate performance for NiCo2O4/RGO hybrid is 3.5 times better than that of NiCo2O4. An asymmetric supercapacitor constructed with NiCo2O4/RGO (positive electrode) and activate carbon (negative electrode) delivered a maximum energy density of 49.6 W h kg-1 and long cycle life. In addition, a flexible transparent supercapacitor device assembled with the NiCo2O4/RGO hybrid electrode achieved a large areal capacity (5.27 mC cm-2 at 75.5% transparency), high energy density (1.17 mW h cm-2) and outstanding mechanical flexibility.
查看更多>>摘要：The hierarchical core-shell heterostructures ZnCo2O4@NiCo2O4 on Ni foam (NF) for supercapacitors were prepared via two-step hydrothermal and electrodeposition reactions followed by two post-annealing treatments. The effect of deposition time on its morphology and electrochemical performance was investigated in detail. Combining high electric conductivity of ZnCo2O4 with high stability of NiCo2O4 as well as synergistic effect, the NF/ZnCo2O4@NiCo2O4-100 (NF/ZCO@NCO-100) integrated electrode exhibited high specific capacitance of 1728.1 F g?1 (240.0 mAh g?1) at 1 A g?1, and excellent long-term stability with 97.8% capacitance retention after 10,000 cycles. The assembled hybrid supercapacitor (HSC) delivered the specific capacitance of 133.6 F g?1 (55.7 mAh g?1) at 1 A g?1 and high energy density of 40.58 Wh kg?1 at 745.62 W kg?1 as well as the outstanding long-term stability of 91.3% capacitance retention after 10,000 cycles. These results provide insights into the rational design of transition metal compound composite materials to construct integrated electrodes for high performance supercapacitors.
查看更多>>摘要：The Cu/Invar bi-metal matrix composites have a great potential to be used as novel electronic packaging materials. In order to clarify effects of the Invar particle size on microstructures and properties of the composites, two Invar powders of average sizes of 26 μm and 105 μm were employed to fabricated the 50 wt% Cu/Invar composites, respectively, by spark plasma sintering (SPS) at 700–800 °C under vacuum condition with a heating rate of 100 °C/min, a pressure of 50 MPa and a holding time of 1 min. The results indicate that the Cu/ fine Invar (f-Invar) composites have finer Cu grain sizes in which the f-Invar particles are semi-continuously distributed. The composites have typical characteristics of low-angle Cu grain boundaries, high-density Σ3 growth twins and Cu/Invar coherent/semi-coherent interface. On the contrary, the coarse Invar (c-Invar) particles are discontinuously distributed in the Cu/c-Invar composites, resulting in the formation of coarser Cu grain sizes, high-angle Cu grain boundaries and non-coherent Cu/Invar interface. Moreover, compared with the f-Invar particles, the c-Invar ones can not only effectively decrease the Cu/Invar interfacial area, but also prohibit the Cu/Invar interface diffusion, therefore considerably improve thermal conductivity (TC) of the Cu/Invar composites at the cost of a little reduction of tensile strength (Rm). It is also clarified that properties of the Cu/Invar composites are sensitive to the sintering temperature. The 700 °C sintered 50 wt% Cu/c-Invar composite has the highest TC of 130.1 W/(m·K). It is very close to the theoretical value predicted by the Maxwell model and much superior to the TCs previously reported in the Cu/Invar composites of the similar Invar fraction.
查看更多>>摘要：Polycrystalline LiCo0.33Ni0.33Mn0.33O2 compounds were prepared via a sol-gel auto combustion synthesis route to examine its conduction mechanism with thermal assessment and a new window of its application as a field emitter is explored. The structural modules and molecular footmarks have been confirmed by XRD, Raman, FTIR, XPS and FESEM techniques. The Nyquist plots (Z′vs.Z′′) exhibits significant contribution of electrode solid interface effect with compared to intra and inter granular contribution. The variation of real and imaginary impedance, modulus, and conductivity spectra with thermal evolution is attributed with the creation of a quasi-particle called “polaron” and the migration of small polaron by tunneling/hopping creates localized state in high temperature. However, a weak crossover between small polaron hopping (SPH) and Mott's variable range hopping (VRH) is observed near 323 K. The colossal dielectric permittivity (?r′)~5 × 106 is originated from inhomogeneous electronic conduction process in LiNi0.33Co0.33Mn0.33O2 due to the creation of absorption current in the flimsy grain boundary which leads to the stockpile of charge carriers in the external-electrode sample interface and induces Maxwell-Wagner electrode interfacial polarization. The exquisite field emission properties were discovered in LiNi0.33Co0.33Mn0.33O2 with low turn-on field@ 1 μA/cm2~2.75 V/μm and threshold field@ 10 μA/cm2~4.39 V/μm with field enhancement factor (β)~4251. The structural and electronic properties of LiNi0.33Co0.33Mn0.33O2 and the local work function (φ)~4.94 eV is computed employing the Density functional theory (DFT). It further supports the conduction mechanism due to self-trapping electrons and strong spin polarization of the O-2p state under applied electric field.
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Elsevier