查看更多>>摘要：? 2022 Elsevier B.V.This work reports on the magnetic, dielectric and structural properties of the nanocrystalline Lu1-xHoxFeO3 (x = 0.0 – 1.0) solid solutions. Ho substitution at the Lu site increases the ground state magnetic moment from 0.245(1) μB per f.u. at x = 0.0 to 4.7 μB per f.u. at x = 1.0. The spin reorientation temperature, TSR, and compensation temperarure, Tcomp, increase with x as ~x2 whereas the Néel temperature, TN, increases as ~x0.4. The variations with x of the ‘field-cooled’ (FC) magnetization, MFC(T=3K,H=100Oe) and the magnetocrystalline anisotropy constant, K1(T=3K), assert that the percolation of the Ho3+ moments and single-ion magnetic anisotropy on the Ho3+ sub-lattices occurs above the threshold concentration of xc≈0.05, which is the minimum Ho concentration for the stabilization of orthorhombic structure in the nanocrystalline Lu1-xHoxFeO3 orthoferrites. A striking similarity between the functional dependences on x of the coercive field, HC, and the magnetocrystalline anisotropy field, HK=2K1/Msat (Msat is the satutation magnetization), indicates that the magnetocrystalline anisotropy on the Ho3+ sub-lattices essentially governs HC(x) at 3 K. Several experimental observations, that firmly support type II multiferroicity in nanocrystalline Lu1-xHoxFeO3, are presented.
查看更多>>摘要：? 2022 Elsevier B.V.Discovery of dopants which can engineer the electronic structure of the thermoelectric materials beneficially to improve the figure of merit has been receiving a lot of attention. In this work, we study one such unique dopant, tungsten in SnTe by implementing first principles density functional theory approach. We predict that tungsten is a n-type resonant dopant which not only increases the band gap but causes convergence of valence sub-bands leading to increased Seebeck co-efficient due to increase in the effective mass and decrease in the bipolar conduction. We show for the first time, the introduction of hyperconvergence in the conduction sub-bands, a feature which was observed only in valence bands of SnTe and GeTe. In addition to the above features, it also introduces multiple electronic valleys near the Fermi level excluding the use of a co-dopant to exploit the benefits of the electronic structure engineering. A maximum ZT of ~1.61 theoretically achieved by tuning the chemical potential at 800 K makes this material worth being explored experimentally.
查看更多>>摘要：? 2022 Elsevier B.V.The effects of Sr doping on the structural properties of Na2BaCo(PO4)2, a spin-1/2 triangular-lattice antiferromagnet as a quantum spin liquid candidate, are investigated by complementary x-ray and neutron powder diffraction measurements. It is found that in Na2Ba1?xSrxCo(PO4)2 (NBSCPO), the trigonal phase (space group P3?m1) with a perfect triangular lattice of Co2+ ions is structurally stable when the doping level of Sr is below 30% (x ≤ 0.3), while a pure monoclinic phase (space group P21/a) with slight rotations of CoO6 octahedra and displacements of Ba2+/Sr2+ ions will be established when the Sr doping level is above 60% (x ≥ 0.6). Such a doping-induced structural transformation in NBSCPO is supported by first-principles calculations and Raman spectroscopy. Na2SrCo(PO4)2, a novel spin-1/2 antiferromagnet with glaserite-type structure, although monoclinically distorted, exhibits no long-range magnetic order down to 2 K and a similar negative Curie-Weiss temperature as Na2BaCo(PO4)2 with a perfect triangular lattice, suggesting the robustness of magnetic exchange interaction against the Ba/Sr substitutions.
Mete B.Aydemir U.Baris Yagci M.Peighambardoust N.S....
13页
查看更多>>摘要：? 2022 Elsevier B.V.Developing non-precious, competent, and environmentally benign electrocatalysts to efficiently drive water electrolysis is critical but at the same time demanding. Layered metal diborides (MDbs) holding attractive features mainly due to the presence of borophene subunits in its crystal structure have lately sparked a great deal of attention for electrocatalytic applications. Here, we highlight the synthesis and electrocatalytic properties of HfB2-based electrocatalysts as Hf1-xTMxB2 (TM = Ni and Co; x = 0.1, 0.2, and 0.3) for both hydrogen and oxygen evolution reactions (HER/OER) under 1 M KOH. Amidst as-prepared samples, Hf0.8Ni0.2B2 and Hf0.8Co0.2B2 appeared to be the best OER and HER catalysts, generating the current density of 10 mA cm?2 at overpotentials of 320 and 430 mV, individually. Concerning the OER, Hf0.8Ni0.2B2 performed an oxygen-evolving process similar to benchmarking RuO2 (an overpotential of 290 mV at 10 mA cm?2) and even more facile kinetics compared to RuO2 with Tafel slopes of 39.5 mV dec?1 vs. 66.2 mV dec?1. In addition, regarding HER, Hf0.8Co0.2B2 displayed an enhanced performance relative to pristine HfB2 (an overpotential of 620 mV at 10 mA cm?2), still inferior to noble metal 10% Pt/C (an overpotential of 198 mV at 10 mA cm?2). Furthermore, the interpretation of Tafel slopes unveils that all samples follow the Volmer path as HER mechanism. Finally, both best-performing electrocatalysts tolerated the current density of 10 mA cm?2 for 20 h, manifesting stable bifunctional catalysts.
Pereira A.F.F.D.F.de Araujo Gomes P.da Costa Pinto C.Ghosh A....
7页
查看更多>>摘要：? 2022 Elsevier B.V.The present work studies the effect of hydrostatic pressure on a biphasic Heusler alloy using in situ X-ray diffraction. A nanostructured biphasic NiTiSn/Ni2TiSn Heusler alloy was synthesized by four hours of mechanical alloying using a vibrational high-energy mill and characterized by x-ray diffraction measurements and Rietveld method. The sample was submitted to high-pressure conditions (up to 11.9 GPa) using a diamond anvil cell (DAC) loaded with He, and the structural evolutions were followed by in situ synchrotron x-ray diffraction. The results validate the stability of the half and full-Heusler alloys, as no pressure-induced structural phase transition was observed over the entire pressure range. The behavior of the crystallographic parameters, equation of state and the compressibility factors for both the Heusler phases were obtained from the experimental results as well from the density functional theory (DFT) calculations. The second-order Birch–Murnaghan equation of state determined from our experimental results yields bulk moduli of 143(9) GPa and 156(6) GPa for the Half and Full Heusler phases, respectively. According to the DFT calculations, the corresponding values are 131.0(9) GPa and 161.8(8) GPa.
查看更多>>摘要：? 2022 Elsevier B.V.Active metals, such as platinum and palladium, were doped in TiZrHfMoNb high-entropy alloy to tune its electronic structure. The electronic structure, activation, and kinetic properties were experimentally investigated. The results indicate that electron transfer occurred between the active metal atoms and other metal atoms after platinum or palladium doping, and that the oxide on the surface was destabilized by active metal doping due to improved activation performance. Therefore, TiZrHfMoNbPt0.0025 could reach a maximum hydrogen storage capacity of 1.749 wt% (1.80 H/M) at around 100 s on the first absorption curve. The electron transfer process is believed to aid in optimizing the electron density of interstitial sites, allowing additional interstitial sites to accommodate additional hydrogen atoms. The presented results provide new insights into the hydrogen storage properties of high-entropy alloys, and it is expected that hydrogen storage capacity can be increased by tuning the concentration and type of doping elements.
查看更多>>摘要：? 2022 Elsevier B.V.Lithium fluorocarbon (Li/CFx) batteries with high-energy density are widely applied in the commercial fields, but their discharge performances are limited due to the presence of electrochemical inactive C–F bonds. Herein, an air-plasma-inducing chemical vapor deposition method is developed to enhance the performance by increasing the concentration of semi-ionic C–F bonds. This novel method helps to reduce the internal resistance (Rb value decreases from 3.46 Ω to 1.83 Ω and Rct value decreases from 110.7 Ω to 40.08 Ω), accelerate the transmission rate, and also improve the specific capacity and energy density. Specifically, the CFx-60 cathode delivers an excellent specific capacity of 676.76 mAh g?1 at 8 C, an energy density of 1184.31 Wh/kg, and a power density of 12,251.46 W/kg. The as-designed strategy is facile and environmentally friendly, which realizes the precise adjustment of atomic-scale massively for CFx battery with excellent performance.
查看更多>>摘要：? 2022 Elsevier B.V.Nano-oxides with low cost are a promising class of reinforcing materials that can be added into solder to enhance reliability of resultant joints. However, the poor interfacial bonding with solder matrix has long been a barrier to its transition from laboratory science to real engineering application. In this study, rare earth Pr and Al2O3 nanoparticles (NPs) were co-added into Sn-0.3Ag-07Cu (SAC0307) solder to solve it, and thermal cycling reliability of resultant joint was found to be much more enhanced when compared to the joints individually added with Pr or Al2O3 NPs. This was attributed to a synergistic effect in-situ built between Pr atoms and Al2O3 NPs, in the form of Pr-coated Al2O3 NPs. This structure helped most Al2O3 NPs maintain nano-scaled during thermal cycling, and thus continuously inhibited the coarsening of interfacial microstructure for a long time. Kinetic analysis showed that the average interfacial IMCs growth coefficient at SAC0307-Pr-Al2O3/Cu interface was about 5.0 × 10?11 cm2/h, lower than that at SAC0307/Cu, SAC0307-Pr/Cu and SAC0307-Al2O3/Cu interface.
查看更多>>摘要：? 2022 Elsevier B.V.The earth-abundant copper species anchored on the -NH2 of NH2-MIL-101(Fe) as noble-metal-free cocatalysts via transient CuII/CuI centers were obtained via a convenient synthesis technique to achieve excellent photocatalytic hydrogen evolution performance in the dye sensitization system. The prepared sample 6Cu-NM-101 exhibited the best hydrogen evolution activity of 5770.96 μmol·g?1·h?1, which was 4.06 times higher than the original NH2-MIL-101(Fe). A series of characterization tests, especially the CV and the Auger Cu LMM, demonstrated that the transient CuII/CuI center played a significant part in the novel ligand to linker metal charge transfer (LLMCT) process. In other words, the electrons could transfer from the lowest unoccupied molecular orbital (LUMO) energy level of the excited state Eosin Y (EY*) to the transient CuII/CuI center to further accelerate the carrier transfer and separation rate. Our work provided a more convenient and effective strategy to prepare various earth-abundant metal ions based on MOFs as low-cost cocatalysts via transient metal centers to boost the photocatalytic hydrogen evolution performance.
查看更多>>摘要：? 2022 Elsevier B.V.The undoped, Mg2+ doped, Ce3+ doped as well as Mg2+:Ce3+ codoped Gd3Al2Ga3O12 crystals were grown from the melt by the micro-pulling down method. Ce3+ and Mg2+ ions were codoped in a wide concentration range. A study of Mg2+ ion concentration effect on the luminescence and scintillation properties as well as segregation of atoms and defects creation processes were carried out. Mg2+ doping in Gd3Al2Ga3O12 led to the creation of OO? defects localized next to Mg2+ sites due to charge imbalance compensation. Consequently, neutral (MgGa/Al/GdOO)x defects were formed. In Ce3+ doped crystals, Mg2+ codoping changed the valence state from Ce3+ to Ce4+ to maintain charge neutrality. Hence, additional neutral (CeGd?-MgGa/Al/Gd′)x and (CeGd-MgGa/Al/GdOO)x defects appeared. Moreover, Mg2+ induced charge imbalance in GAGG crystal might also be compensated by the formation of oxygen vacancies (VO??). The Mg2+ ions imposed defects deteriorated the segregation of atoms. Accordingly the radial inhomogeneity of the crystals was diminished. The presence of stable Ce4+ and defects imposed by Mg2+ ions codoping were proved by absorption, photoluminescence, and scintillation decay time analysis. Hence, Mg2+ codoping resulted in quenching of the Ce3+ luminescence, acceleration of scintillation response, reduction of light yield, and thermally stimulated luminescence. The mechanism explaining a strong luminescence quenching with increasing Mg2+ ions concentration was proposed.
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