查看更多>>摘要：The effects of Co2+ doping on the characteristic adsorption species and optoelectronic properties of the ZnO crystal plane have been simulated by Density Functional Theory (DFT). Because of the linear relationship between the Fermi level density of states and the conductivity, the conductivity is reacted by the Fermi level density of states. The simulated data show the characteristic adsorption species of crystal plane changed before and after doping with Co2+: The characteristic chemisorption species (CCS) O2 molecules disappear after the ZnO (002) plane is doped with Co2+, CCS O2 molecules appear after (200) plane is doped with Co2+, CCS H2O molecules appear after (110) plane is doped with Co2+. The conductivity decreases after doping with three crystal planes. The CCS of O2 molecules has a significant effect on the conductivity. The CCS of H2O molecules has no obvious effect on the conductivity. The effect of O2 molecular coverage rate of CCS on conductivity: The conductivity is proportional to the coverage rate of CCS before doping with Co2+, the conductivity is inversely proportional to the coverage rate of CCS after doping with Co2+. The photocurrent spectrum fitting data is consistent with the regular of experimental data, indicating that the chemical adsorption of characteristic adsorbed O2 and the conductivity of materials can be regulated by crystal plane Co2+ doping, which plays a guiding role in regulating and making use of the characteristic O2 absorption properties of the material plane.
查看更多>>摘要：In this work, Nd2(Zr1-xSnx)3(MoO4)9 (0.02 ≤ x ≤ 0.1) (NZSM) ceramics were successfully obtained through conventional solid-state route. Phase analysis, microstructure, and properties were investigated scientifically by XRD, SEM, and network analyzer, respectively. XRD results revealed that all samples with different substitution amounts of Sn4+ formed the pure phase with R-3c space group. The permittivity was related to the polarizability and the bond of Zr2-O5, the bond of Nd-O2 possessed a positive influence on Q×f. The reduced octahedral distortion and increased bond energy made the temperature coefficient more stable. Infrared reflection spectrum results showed that the permittivity was mainly caused by the absorption of phonon oscillation. The optimum properties (εr = 10.34, Q×f = 74,795 GHz, τf = ?13.55 ppm/°C) were obtained when x = 0.02 sintered at 750 °C.
查看更多>>摘要：The severe interfacial reaction between graphene nanoplatelets (GNPs) and Ti matrix weakened the bonding strength. The severe interfacial reaction was resolved successfully though adding B powders. The B powders distributed on the surface of TA15 powders by low energy ball milling, and then the GNPs coated the mixture powders in the same way. During the process of pre-sintering and canned hot extrusion, a part of B atoms primarily diffused to the vacant sites to form B–C bonds for making up the nanostructure of GNPs, leading to the higher diffusion activation energy of C atoms. The interfacial reaction was inhibited preliminarily. Moreover, Bits of B atoms were adsorbed on the bridge of C–C bond sites, resulting in solubilizing in the (002) plane of GNPs. And the rest of B atoms diffused to the Ti matrix by the way of solution. The diffusion of the C atoms near B atoms was hindered, due to the higher diffusion rate of C atoms, resulting that the interfacial reaction was inhibited further. As a result, the interface with nano-TiC and nano-TiB was obtained. What's more, 0.4% wt% GNPs/TA15 composites with 0.05% wt% B powders exhibited satisfactory mechanical properties with an ultimate tensile strength of 1349 MPa and a fracture elongation of 8.9%. This work provided a new strategy for resolving the severe interfacial reaction to obtain the expectant interface and performance of TMCs.
查看更多>>摘要：In this study, the glass-forming range, microstructural and soft magnetic properties of (Fe1?x-yCoxNiy)86B14 alloys were investigated in the as-cast state and after ultra-rapid annealing. The glass-forming range is seen to be the greatest for Fe-rich compositions and is limited to x ≤ 0.8 and y ≤ 0.3. Within the glass-forming range, this alloy system is observed to contain nano-scale grains with bcc and fcc structures after ultra-rapid annealing and a clear bcc-fcc transition is seen for Ni-rich compositions. Both the coercivity (Hc) and saturation magnetic polarization (Js) for the nanocrystalline (Fe1?x-yCoxNiy)86B14 alloys are generally increased by Co addition and reduced by Ni addition. Js is confirmed to be the largest for (Fe0.8Co0.2)86B14 at 1.88 T in the as-cast state and 1.98 T for (Fe0.7Co0.3)86B14 in the nanocrystalline state. The minimum Hc of 2.0 A/m is obtained for nanocrystalline (Fe0.80Co0.05Ni0.15)86B14 with a Js of 1.71 T. This composition also exhibits a lower core loss compared to the nanocrystalline Fe86B14 and Fe-based amorphous alloys at frequencies up to 1 kHz.
查看更多>>摘要：Two deep-ultraviolet (DUV) transparent nonlinear optical (NLO) materials, AAl3P6O20 (A = Rb, Cs) (I, II), have been elaborately designed from Ba5P6O20 by aliovalent substitution strategy. Both of compounds crystallize in noncentrosymmetric (NCS) C2221 (No. 20) space group with three-dimensional (3D) ∞3Al3P6O20skeleton. The cutoff edges of I and II are lower than 190 nm, which are the shortest ones among the reported Al-based phosphates. In addition, their syntheses, thermal properties, NLO performances are discussed and the first-principles calculation elucidates the origin of the optical properties. This study shows that aliovalent substitution is an effective synthetic route for designing DUV transparent Al-based phosphates NLO materials.
查看更多>>摘要：Low conductivity and shuttle effect of lithium polysulfides (LiPSs) are the major impediments to the development of lithium-sulfurbatteries. Therefore, there is an urgent need for a reasonably designed host to simultaneously meet the needs of sulfur and LiPSs storage and improve the conductivity of the cathode material. In this work, inspired by synergetic effect, we design excellent adsorptive TiO2@yV2O5 (y = 0.025–0.045) bifunctional composites. And the different compositions of matrix material can be fabricated via manipulating the amount of KOH, which combines the advantages of high stability of TiO2 and strong adsorption of V2O5. The V2O5 exists inside TiO2 and part of it is used to provide a cavity, which can buffer volume expansion and store LiPSs and sulfur. The other can enhance the activity and energy of TiO2, thereby go a step further enhance the reaction kinetics. In addition, this TiO2@0.040 V2O5/S electrode exhibits high capacity retention of 91% and 93% at 0.5 C and 1 C after 50 cycles. And the cell exhibits a small polarization (202 mV at 0.1 C, 202 mV at 0.2 C and 234 mV at 0.5 C).
查看更多>>摘要：The temperature and time dependence of the radii of Mg2Si precipitates in 6082 Al alloy under different post-homogenization cooling rates over a wide range of 32–120,000 °C/h were investigated by scanning and transmission electron microscopy. The equivalent radius of the Mg2Si precipitate decreased from 488 to 65 nm, associated with an increase in the cooling rate. The precipitating phase is primarily equilibrium β‐Mg2Si, as inferred from differential scanning calorimetry and X-ray diffraction. With the increasing cooling rate, the hardness of the alloy after T5 heat treatment initially increased and then plateaued. The critical cooling rate was identified to be 760 °C/h. A new thermodynamic particle coarsening model was designed to predict the evolution of particle size during the cooling process, and it presented appropriate agreement with the experimental data. This model can be applied to optimize alloys after the homogenization cooling process to ensure low deformation resistance, improve extrudability, and achieve maximum age-hardening effect in subsequent heat treatments.
查看更多>>摘要：The intermetallic τ11 Al4Fe1.7Si phase is of interest for high-temperature structural application due to its combination of low density and high strength. We determine the crystal structure of the τ11 phase through a combination of powder neutron diffraction and density functional theory calculations. Using Pawley and Rietveld refinements of the neutron diffraction data provides an initial crystal structure model. Since Al and Si have nearly identical neutron scattering lengths, we use density-functional calculations to determine their preferred site occupations. The τ11 phase exhibits a hexagonal crystal structure with space group P63/mmc and lattice parameters of a = 7.478 ? and c = 7.472 ?. The structure comprises five Wyckoff positions; Al occupies the 6h and 12k sites, Fe the 2a and 6h sites, and Si the 2a sites. We observe site disorder and partial occupancies on all sites with a large fraction of 80% Fe vacancies on the 2d sites, indicating an entropic stabilization of the τ11 phase at high temperature.
查看更多>>摘要：The present study reports the enhancement of electrochemical oxygen reduction activity of porous La0.6Sr0.4Co0.2Fe0.8O3?δ (LSCF) cathodes by coating a thin film of Pr-Ni-Mn oxide (PNM5) using a multi-step infiltration process. XRD examination reveals that PNM5 mainly contains a multiphase mixture of Pr6O11, PrNiO3, MnO and NiO. SEM morphology shows a thin PNM5 film and small particles are formed on the surface of LSCF backbone particles. Impedance spectrum analysis indicates that PNM5 infiltrated LSCF exhibits dramatically reduced polarization resistance (Rp), reaching Rp of 0.244 Ω cm2 at 973 K, which is one-half of the baseline LSCF cathode. The activation energy of LSCF cathodes infiltrated with PNM5 is 1.45 eV, slightly lower than the baseline LSCF cathode (1.77 eV). Distribution of relaxation time (DRT) function analysis shows PNM5 infiltration layer significantly promotes the oxygen reduction reaction (ORR) of cathode surface. With the increase in firing temperature, the total resistance increases and Rp changes from ion transport to oxygen reduction reaction. Degradation rate of the PNM5-infiltrated LSCF is also lower, 0.02168% vs 0.07093% for the baseline LSCF over a 200-h period. A single cell testing indicated that the peak power density of the PNM5-infiltrated cell was increased by 140.66%. Overall, PNM5 could be a potential catalyst for boosting the performance of a commercial LSCF cathode for solid oxide fuel cells (SOFC).
查看更多>>摘要：A new organic chemical reduction method was successfully used to synthesize magnesium-coated graphene (GNPs), and xGNPs/AZ91 nanocomposites with different contents were fabricated by vacuum hot-pressing sintering. The microstructure of the composite was mainly composed of the matrix (α-Mg) and the precipitated phase (β-Mg17Al12) with different morphologies such as rods, spindles, and granules. The coarse irregular β phases precipitated along the grain boundaries, while fine rod-like β phases were distributed inside the crystal grains. With the increase of GNPs content, the grain and structure are significantly refined under the action of two mechanisms of increasing the nucleation rate and hindering the growth of grains. The average grain size of the 2.5-wt% GNPs/AZ91 composite dropped from 40.78 μm to 25.39 μm, a reduction of 37.7%. In addition, the orientation relationship (OR) between β-Mg17Al12 and α-Mg was shown as [—3 —1 —1]β-Mg17Al12)∥[1 —1 0 —1]α-Mg. Further, finer β phases were further precipitated in the grain boundaries and matrix. Moreover, the β precipitated phase and the GNP, as well as the GNP and magnesium-matrix formed a nano-scale contact interface and a diffusion bonding interface, thereby greatly enhancing the interface bonding strength between GNP and the matrix. Compared with AZ91 alloy, the grain refinement and load transfer caused by GNPs increased the microhardness of the composite by 17.6% and the friction coefficient was decreased by 37.4%. The significant improvement in the wear resistance of the composites was due to the effect of the lubricating layer formed by GNPs on the wear surface, which changed from severe delamination wear to slight delamination and abrasive wear behavior.
NSTL
Elsevier