查看更多>>摘要：? 2022 The Author(s)In this study, oriented nano-sheets generated during the growth of cobalt-rich Co–V and Co–Zn thin films induced a large anisotropy in the magnetic and transport properties. The regular nano-sheets were tilted 52–54 deg. with respect to the substrate plane, ≈ 3.0–4.0 nm thick, ≈ 30–100 nm wide, and ≈ 200–300 nm long, with an inter-sheet distance of ≈ 0.9–1.2 nm. In spite of the different microstructures of the two kinds of samples where the Co–V films were amorphous, whereas the Co–Zn films showed a growth of Zn nanocrystals, the oblique nano-sheet morphology conferred noticeable shape anisotropy to both specimens. This anisotropy resulted in an in-plane uniaxial magnetic anisotropy. The changes in the nano-morphology caused by thermal treatments, and hence in their anisotropic properties, were studied. While the Co–V samples retained or increased their magnetic and transport anisotropies, this anisotropic behavior vanished for the annealed Co–Zn films. High resolution transmission electron microscopy, HRTEM, including chemical analysis at the nano-scale, and the dependence of the anisotropic resistance on temperature allowed to establish the nature and the activation energy spectra of the atomic relaxation processes during heating. These processes displayed a single peak at 1.63 eV for the Co–V and two peaks at 1.67 and 2.0 eV for the Co–Zn. These spectra and their singularities were associated to the changes induced in the nano-morphology of the films by thermal treatments. The Co–V films retained their nano-sheet morphology almost up to 500 oC; the Co–Zn films lost their nano-sheets at 290 oC. The thermal stability exhibited by the Co–V films makes them useful for applications in ultra high frequency, optical, magnetostrictive and magneto-electric devices.
查看更多>>摘要：? 2022 Elsevier B.V.Temperature dependent oxidation states of ceria (CeO2) are observed at much lower temperatures in presence of silver nano-clusters (NCs), deposited on CeO2 thin-films, using a nano-cluster deposition system equipped with quadrupole mass filter assembly and x-ray photoelectron spectroscopy (XPS) facilities. In situ high-temperature XPS studies indicate that CeO2 oxidizes Ag-NCs to AgO at room temperature and reduces to Ce3+ state at much lower temperature. Further, a temperature dependent reversible change in oxidation states between Ag(III) and Ag(II) states is observed. Transmission electron microscopy (TEM) study reveals that besides coalescence of silver clusters during heating, the Ag-NCs interact with CeO2 resulting in fully covered Ag-NCs by a layer of CeO2 due to strong metal support interactions (SMSI). UV-Vis studies show a decrease in bandgap of CeO2 due to an increase in Ce3+ content in CeO2 film responsible for SMSI effect at the interface of silver clusters and cerium oxide at higher temperature. Interactions at the adsorption edge between CeO2 and Ag-NCs help to decrease the bandgap of CeO2 in presence of Ag-NCs. Thus the presence of silver clusters plays a crucial role in lowering the oxidation-reduction temperature of ceria. Overall, the Ag-NC in ceria helps to reduce Ce4+ state to Ce3+ state at much lower temperature that would be useful for its different low-temperature catalytic applications.
查看更多>>摘要：? 2022 Elsevier B.V.An investigation based on electron microscopy and crystallographic analysis was employed to gain insights into the carbide transformation in MC-M23C6 complex carbide of Haynes282; nanoindentation test and first-principles calculations were performed to study its effect on mechanical properties of the alloy. The results show that MC(M=Ti, Mo)-M23C6(M=Cr, Mo) complex carbide, which exhibits as bull's eye structure, shows an orientation relationship of (131?)MC//(4?20)M23C6, [11?2?]MC//[123]M23C6. Besides, intermediate phase M2C forms at partial MC/M23C6 interface. During creep, Cr diffuses from M23C6 to MC and substitutes Ti under the driving force of concentration gradient. The substitution induces thermal expansion anisotropy in polyhedral clusters of MC, which will trigger the flipping of diagonals and transform MC into M23C6 through the transformation of coordination polyhedron of C atoms from octahedron to twisted cube. The hybridizations, especially the low-energy hybridizations, between C-p, Ni-d, Cr-d and Ti-d orbitals of the atoms located at M23C6/Ni and M23C6/MC interfaces make great contribution to the plentiful chemical bonds formed at the interfaces. These chemical bonds result in the high bonding strength of the two interfaces and thus the beneficial effects of the MC-M23C6 carbides on mechanical properties of the alloy. Moreover, nanoindentation test indicates that MC-M23C6 carbides do a better job of strengthening than individual MC or M23C6 carbide. Therefore, the transformation from MC to M23C6 is detrimental to the mechanical properties of the alloy. The demonstrated concept shed light on the rational design of higher property superalloys for various potential applications.
查看更多>>摘要：? 2022There is no consensus in the literature on the structure and composition of the ε phase of the W-B system, variously reported as WB2 and W2B5. We used ab initio calculations at two levels of theory to identify the stable crystal structure and stoichiometry of this phase. Among the sixteen structures investigated in the composition range of 67–71.4 at% B (WB2–W2B5), nine exhibited unfeasibly high formation energies; the remaining seven were dynamically stable (did not exhibit any soft phonon modes), and satisfied mechanical stability criteria. When including the thermal vibrational contribution to the free energy, all structures with the W2B5 composition lay above the convex hull, suggesting that this composition is metastable, while those with WB2 composition lay on the convex hull or within DFT precison of the convex hull. We found that four of the candidate structures exhibit negative vacancy formation energy, suggesting that the structures are unstable, or that they are naturally hypo-stoichiometric. Combining these results with a comparison of simulated and experimental x-ray and neutron diffraction patterns, we concluded that the ε phase is most likely a hypo-stochiometric W2B5?x compound with space group P63/mmc.
查看更多>>摘要：? 2022 Elsevier B.V.In this study, europium doped GdPO4·H2O were prepared by hydrothermal synthesis. The main goal was to investigate the dependence of the size of nanoparticles on the synthesis conditions. One parameter was changed during each synthesis. The synthesis of Gd0.85Eu0.15PO4·H2O had been performed by changing the volume of solvent (H2O) in the reactor of hydrothermal autoclave meanwhile the number of reagents was kept the same. The pH of the solution had been adjusted by adding nitric acid. Nanorods of various controlled sizes were obtained during the synthesis under these conditions. Samples were analyzed by X-ray diffraction and scanning electron microscopy. The luminescence properties were also measured and discussed in detail, demonstrating the dependence of the emission intensity on the dopant position (bulk or surface).
查看更多>>摘要：? 2022 Elsevier B.V.Rate performance is also a key parameter for silicon to replace graphite serving as anode materials for lithium-ion batteries (LIBs), except for its high theoretical specific capacity. Herein, we fabricated the B-doped Si flakes with high-rate performance from low-cost industrial Si-Ca alloy and B2O3 via a facile molten-salt chemical exfoliation. The layered structure shortens diffusion ways of lithium ions . Moreover, B atoms in Si contribute to the increasement of the conductivity and the expansion of lattices. Benefiting from the doped and layered structure, the B-doped Si flakes electrode exhibits a specific capacity of ~800 mAh g?1 at 2 A g?1 with an initial coulombic efficiency of 81.5% and maintains 85% after 200 cycles. The reversible capacities of ~1250, ~1000 and ~842 mAh g?1 can be delivered at 0.4, 1, and 2 A g?1, respectively. The rational design of a special doped layered structure may propose a strategy for other materials.
查看更多>>摘要：? 2022 Elsevier B.V.A simple method to grow single crystals of α-V2O5 is presented and discussed. Crystal structures of two Wadsley phases, α-V2O5 (Pmmn, Z = 2) and α-V6O13 (C2/m, Z = 2), are studied with single-crystal X-ray diffraction in diamond anvil cells up to 12.8 GPa and 9.4 GPa, respectively, at room temperature. α-V2O5 irreversibly amorphizes above about 7.3 GPa. No phase transition is observed at lower pressures. The polymorph that crystallizes from the amorphous material at high pressures and high temperatures is δ-V2O5 (C2/c, Z = 4) as evidenced by in-situ angle-dispersive synchrotron powder diffraction using large-volume multi-anvil press. No phase transitions were observed during high temperature decompression of the as synthesized δ-V2O5. The crystal structure of α-V6O13 is stable up to at least 9.4 GPa. Present data could be used to achieve better understanding of the high-pressure behavior of related Wadsley phases.
查看更多>>摘要：? 2022 Elsevier B.V.The magnetic and electrical properties of the substituted La0.7Sr0.3Mn1-xCoxO3 perovskite (0 ≤ x ≤ 1) were studied. Analysis of the average spin value obtained from inverse magnetic susceptibility using Curie–Weiss law for the samples suggested Co4+ ions were in the high spin state, whereas the spin state of Co3+ ions transformed from high spin to intermediate-spin state at x= 0.8. The metallic conduction behavior of the x = 0 and x = 1 samples was analyzed using the empirical equation ρt=ρ0+ρ2T2+ρ4.5T4.5, reflecting the importance of electron–magnon scattering effects similarly to other manganites. All the other samples displayed semiconductor-like behavior throughout the studied temperature range. The resistivity data in semiconducting La0.7Sr0.3Mn1-xCoxO3 could be fitted to the model of variable range hopping, and both hopping distance and average hopping energy reduced with increasing doped Co concentration.
查看更多>>摘要：? 2022 Elsevier B.V.The advanced new Er3+/Yb3+: Na3Zr2(SiO4)2PO4 (NASICON) monoclinic phosphors prepared by solid state reaction technique has been analyzed as upconverting materials. The crystal phase, structural parameters, surface morphology, different functional groups and bandgap of the synthesized phosphors have been analyzed. Under 980 nm continuous wave diode laser excitation, the codoping of Yb3+ ions in the Er3+ doped phosphors exhibit fascinating results. Stark sublevels observed in the upconversion emission have been used for the fluorescence intensity ratio (FIR) based thermometry. Relative & absolute sensitivity, thermal stability and temperature dependent CIE have been determined. The thermally stable Na3Zr2(SiO4)2PO4: Er3+/Yb3 phosphors with high color purity can be utilized in sensing, display and security purposes.
查看更多>>摘要：? 2022 Elsevier B.V.Magnesium hydride (MgH2) is an ideal solid hydrogen storage material and on-line hydrolysis hydrogen source. However, the synthesis of MgH2 usually requires harsh conditions of high temperature, high pressure and long duration, bringing great challenges to production cost and safety. In this paper, MgH2 is prepared by hydriding combustion synthesis (HCS) and the mechanism of improving Mg hydrogenation properties by the in-situ formation of Al* is revealed. Under low hydrogen pressure of 1 MPa, the hydrogenation degree of Mg can be greatly increased from 9.6% of pure Mg to 90.5% with 10 mol% Al added. In the activation stage, Al reacts with Mg to form Mg17Al12, which brings rich grain boundaries and provides rapid diffusion channels for hydrogen. Subsequently, in the hydrogenation stage, Mg17Al12 reacts with H2 to generate Al* in-situ, which are evenly distributed and act as nucleation sites for MgH2. Hydrogen molecules diffuse rapidly along the interface between Mg/MgH2 and Al* and are easily adsorbed and dissociated on the surface of nano-scale Al* . The unique disproportionation hydrogenation reaction of in-situ forming highly active metallic substances as excellent catalysts provides a new idea for the modification of Mg-based hydrogen storage materials.
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