查看更多>>摘要：Lanthanide metal-organic frameworks (Ln-MOFs) have been widely used in fluorescence sensing, bioimaging and light emitting diode due to their excellent optical properties. However, the preparation of Ln-MOFs is energy and time-consuming due to the constraints of the conventional wet chemical methods. In this paper, a synthetic strategy for the rapid preparation of Ln-MOFs nanorods with adjustable emission wavelength in a microchannel reactor is proposed. Compared with the wet chemical methods, the efficient mass and heat transfer capability of the microchannel shortens the reaction time from 12 h to 50 min. More importantly, Ln-MOFs nanorods with different emission wavelengths can be easily prepared by adjusting the flow rate of different components of the microchannel, which can be adjusted in real-time according to the preparation needs. The result shows that the Ln-MOFs prepared by microfluidic method is in the shape of nanorods with widely emission wavelength from 470 nm (blue light) to 615 nm (red light). In addition, the fluorescence emission intensity of Ln-MOFs is confirmed to have a wide reversible temperature (30–220 ℃) and is expected to be used for high-precision temperature sensing in the future.
查看更多>>摘要：ZnGa2O4 is an important cathodoluminescent material which exhibits good near-infrared long afterglow characteristics after being Cr-doped into Ga sites (ZGO: Cr). The band structure, crystal structure and optical properties of ZGO: Cr are investigated by using first-principles calculations based on density functional theory. It is found that, in the ZGO: Cr system, due to the presence of the Cr-O bond, the distortion of the local lattice goes up as the Cr3+ doping amount increases. Meanwhile, impurity levels appear near the Fermi level of the ZGO system, and the orbital controlling the conduction band bottom gradually moves from the Ga-4s orbital to the Cr-3d orbital. Consequently, the real optical band-gap of the ZGO: Cr system becomes narrower, and the absorption edge undergoes a red-shift. The density of states of all upward and downward atomic spins is distributed asymmetrically, indicating that ZGO: Cr exhibits a certain amount of spin polarization. Additionally, the static dielectric constant of the ZGO: Cr material system increases with the increase in the Cr3+ doping amount. According to the findings, adjustments can be made of the doping concentration and energy range in the optical applications of ZGO: Cr material system.
查看更多>>摘要：Fe-Co alloy nanoparticles of different compositions (Fe content of 76, 51, and 30 at%), along with pure Fe and Co nanoparticles, were prepared by pulsed-laser inert gas condensation, consisting in laser ablation of Fe-Co alloy targets under helium atmosphere. From the morphological point of view, the obtained nanoparticles have nearly spherical shape, follow a lognormal size distribution and exhibit little aggregation. X-ray diffraction and high-resolution electron microscopy coupled with electron energy loss spectroscopy show that the Fe-Co nanoparticles are single crystals with body-centered cubic structure. Furthermore, in the majority of nanoparticles the composition is highly uniform across the whole diameter and there is little variation in composition from one nanoparticle to another. Exposure to non-inert atmosphere leads to the formation of a core@shell metal@oxide morphology characterized by a spinel oxide shell of 2–3 nm around the metallic alloy core. All samples display a ferromagnetic behavior, characterized by a hysteretic magnetization loop. The saturation magnetization attains a maximum value of 2.43 Bohr magnetons per atom for Fe content of 76 at%, in agreement with the Slater-Pauling curve for alloys of 3d elements. Instead, the coercive field, ranging from 29 to 60 kA m?1, is much larger than the reported values for polycrystalline bulk Fe-Co compounds and monotonically increases from pure Fe to pure Co. These results demonstrate that pulsed-laser inert gas condensation allows to prepare high-quality nanoalloys with tailorable magnetic properties, overcoming the limitations of thermal evaporation methods with respect to compositional control.
查看更多>>摘要：Compounds that have polymorphism at ambient conditions exhibit interesting structural transitions under different thermodynamic conditions. The compound Gd2Si2O7 is an interesting silicate that exhibits polymorphism at ambient conditions. We have investigated high pressure behavior of orthorhombic Gd2Si2O7 using Raman spectroscopy and identified structural changes at pressures 2 and 8 GPa followed by transformation to a disordered/glassy phase above 13 GPa. While the transitions are reversible from 12 GPa, releasing from higher pressures leads to recovery of a glassy phase. We have carried out density functional theory (DFT) simulations for the high-pressure structural optimization of the different phases of Gd2Si2O7. The enthalpy cross over as obtained from DFT simulations predicts the high-pressure phase above 2 GPa to be triclinic and the phase above 8 GPa to be monoclinic Gd2Si2O7 which support the experimental findings. The random change of Si-O bond length above 20 GPa points towards possible amorphization for the monoclinic phase.
查看更多>>摘要：The stray grains formation associated with constitutional supercooling during plasma re-melting of Ni-based single crystal superalloy is investigated based on the temperature field simulation and actual substrate orientation. The calculated melting pools and dendrite growth directions consist with the experimental results. The Gd and Vd distribute non-symmetrically, different from Gn and Vn. The Gd is lower while the Vd is higher in the region near the boundary of [1?00] and [01?0] dendrite zones. As a result, the Gd/Vd in this region is lower. The Gd/Vd evaluates the degree of constitutional supercooling and the threshold value 1.3 × 107 K s/m2 is obtained for the equiaxed stray grains formation. The equiaxed stray grains forming in the region with Gd/Vd lower than the threshold value are intimately associated with constitutional supercooling, while the stray grains generated in the region near the boundary of melting pool closest to the substrate are independent of that. The origin of stray grains outside these two regions is probably same as that in the region near the boundary of melting pool closest to the substrate. Meanwhile, the strip-shaped stray grains develop due to the active<100>direction close to the direction of maximum temperature gradient.
查看更多>>摘要：Pb0.925La0.05Zr0.95Ti0.05@xwt%SiO2 (PLZT@xwt%SiO2, x = 0, 1, 2, 3 and 4, marked as S0, S1, S2, S3, S4 respectively) ceramics were prepared by combining conventional sol-gel method with St?ber method, the microstructure, electrical properties and energy storage characteristics were comparatively investigated. TEM analysis prove that samples S1, S2 and S3 present core-shell structures. SEM results indicate that SiO2 weakens the crystallinity of the ceramics and restricts the grain growth of all the specimens. When the concentration of SiO2 is 3 wt%, the sample shows better energy storage characteristics, the value of Wre of this sample can reach 2.29 J/cm3; In addition, temperature (T) will induce a phase change in the sample. When T < 50 ℃, sample S3 is ferroelectric phase, when T is in the range of 50–130 ℃, sample S3 is coexistence of anti-ferroelectric and ferroelectric phase, showing double electric hysteresis loops. In this temperature range, the temperature stability of sample S3 is the poorest, and the increases in Wre density and η are 317.39% and 25.04%, respectively. The core-shell structure samples prepared by the St?ber method can increase the energy storage density by reducing the turnover electric field. The energy storage density has increased from 0.3 J/cm3 to 2.29 J/cm3.
查看更多>>摘要：The factor that plays important role in the quality of the final product in selective laser melting (SLM) is the process parameter set used in production. In general, these fabrication parameter sets are obtained experimentally by using the energy density requirements of the material. The experimental investigation is partly a trial and error approach, which is a time and cost-consuming process. On the other hand, keeping the temperature of the melt pool in an allowable range, which is dominated by the applied process parameters sets, and preventing temperature fluctuations impress the stability of the production and therefore the quality of the final product. The paper presents a multiphysics numerical model approach for obtaining parameters in an SLM process by using AlSi10Mg powders as the material medium. The proposed approach provides mathematical relationships between the process parameters and the temperature they form. By investigating the effect of laser power and laser spot diameter on the temperature at different scanning velocities, wider process parameter sets were obtained for AlSi10Mg. In addition, mathematical relationships between laser power-temperature and laser spot diameter-temperature at different scanning velocities, which will be the base material to design a controller to control the melt pool temperature instantly, were developed. By using the parameter sets obtained from the simulations, test samples including samples for microstructure study and tensile test specimens were fabricated to validate the model. The un-melted powders and nonconnected melt pool defects due to insufficient temperature, evaporation defects caused by extreme temperature, and appropriate and homogeneous microstructures as a result of suitable parameters that were predicted through simulations, affecting microstructure and mechanical properties, validated the model. The experimental study was carried out by examining the microstructure and tensile properties of the fabricated test samples.
查看更多>>摘要：Thin film metallic glasses (TFMGs) have attracted great attention due to their excellent functional properties and ease of fabrication as compared with bulk metallic glasses. Among them, TaW-based TFMGs have rarely been studied so far. Here, a novel Ta46.5W35Co18.5 TFMG was successfully developed using a magnetron co-sputtering system. The Ta46.5W35Co18.5 TFMG exhibits high hardness of 12.3 GPa, high elastic modulus of 159 GPa, pronounced plastic deformation behavior, and excellent corrosion resistance, i.e., low passive current density of 7.65 × 10?6 A/cm2 and high corrosion potential of 0.31 V, as well as good thermal stability with high onset crystallization temperature of 1100 K. In addition, the origin of these excellent properties was also investigated in detail by using X-ray diffraction and high-resolution transmission electron microscopy. It was found that, for the Ta46.5W35Co18.5 TFMG, its excellent corrosion resistance may be attributed to the amorphous structure, and the high hardness and good plastic deformation ability are caused by the unique atomic-scale structure with nanocrystals dispersed in the amorphous matrix. This work provides a useful guideline for developing TFMG system combined with excellent corrosion resistance, high hardness, and good thermal stability.
查看更多>>摘要：P-type inorganic materials show great potential as the hole transport layers in perovskite solar cells due to their low cost and enhanced chemical stability. As a p-type semiconductor, although AgCuO2 has a high hole mobility, it has not received much attentions so far. Herein, we introduce a one-step synthesis of AgCuO2 nanocrystalline films on conductive substrates by electrochemical deposition and use them as hole transport layers in perovskite solar cells. The electrodeposited AgCuO2 films exhibit smooth and pin-hole free morphology with high transmittance and good conductivity. Ultraviolet photoelectron spectroscopy also shows that the energy level of the AgCuO2 film matches well with the perovskite layer. Finally, the inverted perovskite solar cells based on AgCuO2 obtain a power conversion efficiency of 10.24%. This is the first study to demonstrate the successful use of AgCuO2 in perovskite solar cells. Moreover, it can be predicted that the ternary AgCuO2 will open up a new path for inorganic hole transport materials in the field of solar cells.
查看更多>>摘要：Introduction of oxygen vacancies on the surface of photocatalyst has been prove to be an impactful channel to boost the photocatalytic activity, which can restrain the recombination of photoactivated carriers and produce defect energy level. Plasma surface treatment can change the stability of the crystal structure, increase the specific surface area of the materials, and produce more oxygen vacancies. In this study, plasma was used to treat BiVO4 under different atmospheres (Ar, N2, H2) to further exalt the photocatalytic capability of BiVO4 with rich oxygen vacancies. X-ray photoelectron spectroscopy and low-temperature electron paramagnetic resonance spectrometer confirmed that oxygen vacancies rich BiVO4 photocatalysts were all successfully fabricated under the different atmospheres. Moreover, Bi0 was in-situ generated on the surface of BiVO4 under H2 atmosphere treatment. Under N2 atmosphere treatment, a new N 2p energy level can be established. Under Ar atmosphere treatment, a new energy level established by oxygen vacancies is formed. The catalytic capability was assessed by decomposition of rhodamine B and tetracycline. Interestingly, after treated under the H2 atmosphere, the degradation ability of Bi0/OVs-BiVO4 for rhodamine B and tetracycline disintegration is 3.1 and 3.3 times of that of the reference BiVO4, respectively. The photocatalytic enhancement mechanism of BiVO4 treated by plasma under different atmospheres was proposed.
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Elsevier