查看更多>>摘要：Cu/Cu-Zr-Al metallic glass composites (C/CMGCs) are high-strength conductive materials that have been synthesized by a combination of ball milling (BM) and spark plasma sintering (SPS). This study investigated how the rotational speed of BM process before SPS consolidation affects the microstructure, mechanical properties and electrical properties of fabricated bulk C/CMGCs were investigated. Increasing the BM speed significantly enhanced the mechanical strength while maintaining a high electrical conductivity. However, when the speed exceeded 375 rpm, the high centrifugal force hindered effective impact between the balls and powder to impede further performance optimization. Using the grain boundary strengthening strategy, nanocrystalline copper was strengthened by tuning the milling parameters. The simultaneous achievement of high conductivity and superhigh strength in the C/CMGCs will prompt further explorations of functionalized bulk metallic glass composites with vast untapped potentials.
Abdelrehman M.H.M.Kroon R.E.Yousif A.Seed Ahmed H.A.A....
14页
查看更多>>摘要：Yb3+ and Er3+ co-doped Gd2O3:Bi3+ phosphor were prepared via a combustion method. The structural properties and surface morphology of the phosphors were studied with X-ray diffraction and a scanning electron microscope. UV–visible absorption, photoluminescence and cathodoluminescence (CL) spectra were also investigated. The optical bandgap of Gd2O3 increased with additional doping. The visible emission confirmed that the Gd2O3:Bi3+ co-doped with Yb3+ is located in the blue and green band regions related to the Bi3+ in the S6 and C2 symmetry sites. The near-infrared (NIR) down-conversion (DC) emission intensity increased upon increasing the Yb3+ concentration. The visible Bi3+ emission was reduced when adding a higher Yb3+ ion concentration while the NIR emission increased due to the energy transfer from the Bi3+ to the Yb3+ ions. UV-Vis energy excitation photons were successfully converted into NIR photons. The up-conversion (UC) visible emission spectra of Gd2O3:Bi3+ co-doped Er3+ consisted of two strong green, weak red and NIR emission bands. The 980 nm infrared excitation was successfully converted into UV-Vis emission. The CL emission spectra confirmed blue emission bands assigned to the 3P1 → 1S0 transitions of the Bi3+ ions and the green-yellow emission bands corresponded to an overlap between the 3P1 → 1S0 transitions of the Bi3+ ions and the 2H11/2, 4S3/2 → 4I15/2 transitions of the Er3+ ions. A significant enhancement of the emission intensities of Yb3+ and Er3+ ions was observed after Bi3+ doping. The results indicated that Gd2O3 materials based on the Bi3+–Yb3+ and Bi3+–Er3+ couples may be possible phosphors for improving photovoltaic conversion efficiency via spectral modification utilizing the DC and UC processes.
查看更多>>摘要：In this work, the Er-doped Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystal with a large size was successfully grown by the modified Bridgman technique. The temperature dependent phase structure, domain configuration and electromechanical properties of the single crystal with the composition of 2 wt%Er-0.66PMN-0.34PT (Er-0.66PMN-0.34PT) were investigated in detail. For [001]C oriented Er-0.66PMN-0.34PT single crystal, it is found that the room temperature phase structure is the coexistence of rhombohedral (R) and monoclinic (M) phases and M phase is dominated. The piezoelectric constant d33 through the converse piezoelectric effect is about 2410 pC/N. The phase transition from R+M to tetragonal (T) phase begins at 80 ℃ and finishes at 120 ℃. Between 80 ℃ and 120 ℃, the single crystal belongs to the coexistence of R, M and T phases. At 135 ℃, the T phase and polar nanoregions (PNRs) transform into cubic phase and PNRs. The compliance constantss33Dand s33E, longitudinal coupling factor k33 and piezoelectric constant d33 increase by 32%, 77%, 34% and 133%, respectively, with temperature increasing from 22 ℃ to 80 ℃. The ultrahigh increase of d33 is derived from the increase of dielectric constant due to easier polarization rotation and domain wall movement at elevated temperature. Our results will helpful for the study of rare-earth doped relaxor ferroelectric single crystals.
查看更多>>摘要：In this work, the effect of Sb addition on the microstructure and mechanical properties of Mg2Si phase in Mg2Si/AZ91 composites are investigated by experimental research and first-principles calculation. The experimental results show that the coarse dendritic shape is modified to blocky polygonal shape, and the size of primary Mg2Si, is successfully refined with the Sb addition. With enhancing Sb addition contents, the doping concentration of Sb in Mg2Si phase keeps increasing, which accounts for the morphology and size modification. Besides, nano-indentation tests reveal that the Young's modulus of Mg2Si phase exhibits less reduction, while the hardness is significantly improved when introducing 2.0 wt%Sb. The calculated results indicate that the structure stability of Mg2Si crystal is enhanced, and the mechanical modulus including bulk modulus, shear modulus and Young's modulus of Mg2Si are decreased with the increase of Sb concentration, agreeing well with experimental observation, but the hardness reduces, which is contrary to the experimental results. Mg2Si phase doping with Sb atoms, however, exhibits improved ductile behavior compared with undoped Mg2Si due to the increased Poisson's ratio and B/G ratio. In addition, Sb doping can weaken the bond strength and reduce the population of Mg-Si covalent bonds, as well as generate new Mg-Sb bonds with lower strength based on the electronic structure analysis, which contribute to the decrease of mechanical modulus.
查看更多>>摘要：Photocatalysis technology has attracted great attention in the field of wastewater purification for plantation purposes. In the present work, we report the preparation, characterization, and application of flexible γ/γ′ -Bi2MoO6/N-doped carbon (Bi2MoO6/N-C) nanofiber membranes in tetracycline (TC) treatment and Vigna radiata growth. The phytotoxicity of degraded intermediates in treated water was evaluated for seed germination and growth of Vigna radiata. The as-prepared flexible Bi2MoO6/N-C homojunction nanofiber membrane, composed of subunits of γ-Bi2MoO6 nanoparticles and γ′ -Bi2MoO6 nanorods, showed strong visible-light harvesting capability, and good photogenerated electron-hole separation, which displayed the better photocatalytic efficacy in the TC treatment, in terms of degradation rate (97%, 60 min), and recyclability (4 cycles). Further, the germination and growth of Vigna radiata seeds were used to check the phytotoxicity level of the photocatalyst itself (0–10,000 mg/L), the treated and untreated TC solution. Phytotoxicity studies were undertaken via growing Vigna radiata in this Bi2MoO6/N-C photocatalyst solution and treated TC solution. The results demonstrated that Vigna radiata thrived in photocatalyst solution even at a high concentration of 10,000 mg/L and TC solution treated by the photocatalyst. Our work could afford an effective multifunctional photocatalyst for improving water quality for irrigation and plantation purposes.
查看更多>>摘要：Electrochemical nitrogen reduction reaction (NRR) with nitrogen as the raw material under environmental conditions is regarded as a promising approach to replace the Haber-Bosch process. Nevertheless, identifying an efficient electrocatalyst to improve NRR activity is confronted with challenges. Here, porous graphitic carbon nitride (g-C3N4) was doped with cobalt through hard-template method. The resulting g-C3N4-based electrocatalyst achieved a high ammonia yield rate (49.69 μg·h?1· mgcat.?1) and Faradaic efficiency (32.20%) at a low overpotential of ?0.1 V vs. RHE, exceeding those of some previously reported g-C3N4-based electrocatalysts. First-principle calculations revealed that the work function and band gap of catalyst decreased after doping Co, indicating that the introduction of Co promoted the charge transfer. The band center showed an upward shift in Co-doped porous g-C3N4, which may have compensated for the selective adsorption of N2. This work manifested the potential applications of heteroatomic doping in designing NRR catalysts.
查看更多>>摘要：Photocatalytic nitrogen (N2) fixation provides a green avenue for the production of ammonia (NH3), which is extremely significant for global biogeochemical cycle. However, there is still lack of highly efficient catalyst to improve the N2 photofixation efficiency. In this work, oxygen vacancy engineered perovskite SrTiO3 materials have been prepared by post reduction using lithium alkylamine solution and served as effective catalysts for visible-light-driven N2-to-NH3 conversion. The formation and concentration of oxygen vacancies were confirmed by electron paramagnetic resonance, X-ray photoelectron spectroscopy and thermogravimetric analyses. The SrTiO3 catalyst with optimized oxygen vacancies concentration exhibited improved photocatalytic N2 reduction rate of 306.87 μmol·g?1·h?1, which is approach ten-fold higher than that of pristine SrTiO3. Electrochemical impedance spectroscopy and photoluminescence measurements reveal that optimum amount of oxygen vacancies can promote the effective adsorption of N2 molecules and improve the photocatalytic performance by facilitating the fast separation of photo-generated charge carriers. Moreover, the as-fabricated defective SrTiO3 exhibited outstanding stability, which makes it emerge the promising potential for further practical applications. This work offers a feasible method for the design of high performance photocatalysts through defect engineering.
查看更多>>摘要：Supercapacitance electrode materials with rapid charging/discharging performance are considerably useful in practical applications for time saving. However, the supercapacitance performance of the electrode materials is sharply degraded with the increase in current density. To achieve fast energy storage for portable devices, bimetallic nickel cobalt phosphides (NiCoPs), composed of special fingerprint-like nanosheets (NSs), are developed as electrode materials, which exhibit a high specific supercapacitance under large charging/discharging current density. The NiCoP NSs are assembled using entangled nanowires with a wide pore size distribution through hydrothermal and phosphorization reactions. The influence of phosphorization temperature on the morphologies, chemical compositions, and supercapacitance performance of NiCoP compounds is investigated. Electrochemical tests show that the fingerprint-like NiCoP NSs deliver a high specific capacitance of 2360, 1900, and 900 F g?1 at 1, 20, and 50 A g?1, respectively, indicating outstanding capacity retentions of 81% (1–20 A g?1) and 38% (1–50 A g?1) at large charging/discharging current density. The assembled asymmetric supercapacitor of NiCoP//activate carbon presents an energy density of 156 Wh kg?1 at 1331 W kg?1 and maintains 67.5 Wh kg?1 at 27000 W kg?1 in aqueous KOH electrolyte. The bimetallic NiCoPs with a tunable fingerprint-like structure can enhance conductivity, provide nanoporous channels, and facilitate fast electrochemical reactions, which are remarkably beneficial for rapid energy storage and conversion applications.
查看更多>>摘要：Due to their excellent light absorption and photovoltaic effects, transition metal dichalcogenide-based heterojunctions have been widely investigated as materials for optoelectronic devices. This work presented a MoS2 film preparation process using electron beam evaporated MoO3 films as the precursor layer. The prepared MoS2 film was used in the self-powered MoS2/Al2O3/n-Si photodetector, which showed high responsivity (1.15 A W?1), normalized detectivity (1.28 × 1011 Hz1/2 cm/W) and photoresponse (τr = 28 μs) without external bias. Besides, the photodetector exhibited a large frequency-photoresponse range (up close to 100 kHz). Moreover, attributed to the excellent MoS2 quality and the effective interface passivation by ALD-deposited Al2O3, the high-speed photoresponse of the photodetector was realized. These results demonstrated the potential of applying MoS2 material prepared from electron beam evaporated MoO3 precursor layers in the high-frequency and fast photoresponse photodetectors.
查看更多>>摘要：The coarsening and inhomogeneous distribution of nano-grains caused by traditional heat treatment processes are the biggest obstacles for obtaining ultrahigh permeability and excellent comprehensive soft magnetic properties in Fe-based nanocrystalline alloys. Here, we propose a new strategy to control grain growth and magnetic anisotropy, by introducing isotropic compressive stress field in the annealing process to optimize the magnetic properties. Compared with conventional isothermal annealing, the coupling of stress-temperature field generated by hot isostatic pressing (HIP) induced the microstructure, magnetic domain evolution and magnetic properties in Si-rich Fe73.5Si15.5B7Nb3Cu1 amorphous ribbons have been systematically investigated. We demonstrate that HIP treatment promotes more Si atoms to dissolve in Fe unit cell to form Fe(Si) solid solution causing an increase in interplanar spacing. Also, the high-density Cu clusters precipitate in the amorphous matrix upon HIP serving as nucleation sites for α-Fe(Si) grains, which facilitate a high volume fraction, uniform and ultrafine-grained microstructure. Moreover, the existence of stress field introduces induced anisotropy effectively controls the magnetization mechanism and magnetic structure evolution. Furthermore, the Fe73.5Si15.5B7Nb3Cu1 nanocrystalline alloy treated by HIP exhibit excellent comprehensive magnetic properties, such as high Ms, high μe, low Pcv, low AC Hc and high Br/Bm.
NSTL
Elsevier