Homogenous coating of Li^(+)conductive Li_(5)AlO_(4)on single-crystalline nonstoichiometric Li_(1.04)Ni_(0.92)Al_(0.04)O_(2)for rechargeable lithium-ion batteries

Cobalt-free,nickel-rich LiNi_(1-x)Al_(x)O_(2)(x≤0.1)is an attractive cathode material because of high energy density and low cost but suffers from severe structural degradation and poor rate performance.In this study,we propose a molten salt-assisted synthesis in combination with a Li-refeeding induced aluminum segregation strategy to prepare Li_(5)AlO_(4)-coated single-crystalline slightly Li-rich Li_(1.04)Ni_(0.92)Al_(0.04)O_(2).The symbiotic formation of Li_(5)AlO_(4)from reaction between molten lithium hydroxide and doped aluminum in the bulk ensures a high lattice matching between the Ni-rich oxide and the homogenous conductive Li_(5)AlO_(4)that permits high Li^(+)conductivity.Benefiting from mitigated undesirable side reactions and phase evolution,the Li_(5)AlO_(4)-coated single-crystalline Li_(1.04)Ni_(0.92)Al_(0.04)O_(2)delivers a high specific capacity of220.2 mA h g^(-1)at 0.1 C and considerable rate capability(182.5 mA h g^(-1)at 10 C).Besides,superior capacity retention of 90.8%is obtained at 1/3 C after 100 cycles in a 498.1 mA h pouch full cell.Furthermore,the particulate morphology of Li_(1.04)Ni_(0.92)Al_(0.04)O_(2)remains intact after cycling at a cutoff voltage of 4.3 V,whereas slightly Li-deficient Li_(0.98)Ni_(0.97)Al_(0.05)O_(2)features intragranular cracks and irreversible lattice distortion.The results highlight the value of molten salt-assisted synthesis and Li-refeeding induced elemental segregation strategy to upgrade Ni-based layered oxide cathode materials for advanced Li-ion batteries.

Microstructure and electrochemical characteristics of nonstoichiometric La-rich AB_5-type alloy for Ni/MH battery electrode

The nonstoichiometric La-rich mischmetal (designated by MI)-based hydrogen storage alloy with a composition of MI(Ni0.64Co0.2Mn0.12Al0.04)(4.76) was prepared by arc melting and annealed at 1173 K for 10 h to investigate the effect of annealing treatment on the microstructure and electrochemical characteristics of the alloy. X-ray diffraction analysis showed that annealing can cause a release of the crystal lattice strain and an increase in amounts of the La2Ni7-type second phase in MI(Ni0.64Co0.20Mn0.12Al0.04)(4.76) alloy. Scanning electron microscopy and electron probe microanalysis examinations indicated that annealing leads to disappearance of the dendrite structure in the as-cast alloy, growth of crystal grain, and decrease of composition segregation. The annealing at 1173 K for 10 h flattened and extended the potential plateau and increased the maximum discharge capacity to 328 mA center dot h/g from 310 mA center dot h/g and the cycling life. The mechanism of the improvement in electrochemical characteristics was discussed based on the alloy microstructure change induced by annealing.

Dumb-bell Structures of Nonstoichiometric La(Ni, Sn)_(5+x) Alloys and Their Relationships with the Preparation Methods

Crystal structures of nonstoichiometric La(Ni, Sn)5+x (x = 0.1～0.4) alloys prepared by different methods were investigated by using powder X-ray diffraction and Rietveld refinement analysis. Space group of this type of alloys belongs to P6/mmm, in which Sn only occupies the 3g sites. It has been demonstrated that some of the 1a sites of the nonstoichiometric alloy are replaced by the NiNi dumb-bells which have a strong correlation with the anisotropic thermal parameter B33. The preparation methods have an effect on the number of dumb-bells that can substitute the 1a sites. It was found that the annealed alloys have more NiNi dumb-bells in the structure than the rapid solidified and as-cast alloys have while still keep good crystallinity.

Fabricationofcerium-dopednonstoichiometric(Ce,Lu,Gd)_(3+δ)(Ga,Al)_(5–δ)O_(12) transparent ceramics

Cerium-doped nonstoichiometric （Ce,Lu, Gd）3＋δ,（Ga,A1）5-δO12 （LuGGAG） transparent garnet ceramic samples were fabricated via a solid state reaction method in this study. The ceramics were prepared via oxygen sintering followed by hot isostatic pressing （HIP）. The phase and microstructure of the samples were analyzed by X-ray diffraction and scanning electron microscopy （SEM）, respectively. The excitation, emission and transmission spectra were also measured. The total optical transmittance of the annealed LuGGAG ceramics with thickness of 3 mm reached 47% at the emission wavelength of 555 nm. The decay time was about 60 ns. Compact microstructure of polycrystalline grains with scale around 5 μm were gained according to scanning electron microscopy characterization. The successful preparation of the bulk ceramic material and implementation of the combined oxygen sintering-hot isostatie pressing treatment process provided an important method for the exploration of nonstoichiometrie scintillator material.

Cation ratio and oxygen defects for engineering the magnetic transition of monodisperse nonstoichiometric zinc ferrite nanoparticles

Monodisperse nonstoichiometric zinc ferrite nanoparticles with a tunable size of 4.1–32.2 nm are fabricated via thermal decomposition. An extrinsic impurity phase of the ZnO component is present in the zinc ferrite nanoparticles with a size of <10 nm, but this phase can be eliminated after the air annealing treatment. The atom ratio of Zn/Fe and concentration of oxygen vacancies decrease as the particle size of zinc ferrite increases, causing magnetic transition from superparamagnetism to ferromagnetism. The X-ray magnetic circular dichroism spectra reveal that the spin magnetic moments of Fe^(3+)are reduced, and the orbital magnetic moments are frozen with the increasing atom ratio of Zn/Fe. Therefore,saturation magnetization decreases. The saturation magnetizations of all the zinc ferrite nanoparticles decrease after the air annealing treatment, suggesting that oxygen vacancies considerably influence the magnetic properties. The air annealing treatment can minimize the number of oxygen defects,which trigger some of the Fe^(3+)–OV–Fe^(3+)ferrimagnetic couplings to transfer into the Fe^(3+)–O^(2-)–Fe^(3+)antiferromagnetic couplings. This work provides new insights regarding the magnetic performance of spinel ferrites by tuning the stoichiometric ratio and oxygen defects.

Enhanced dual plasmonic photocatalysis through plasmonic coupling in eccentric noble metal-nonstoichiometric copper chakogenide hetero-nanostructures

The extension of plasmonics to materials beyond the conventional noble metals opens up a novel and exciting regime after the inspiring discovery of characteristic localized surface plasmon resonances(LSPRs)in doped semiconductor nanocrystals originating from the collective oscillations of free holes in the valence band.We herein prepare colloidal monodisperse eccentric dual plasmonic noble metal-nonstoichiometric copper chalcogenide(Au@Cu_(2-x)Se)hybrid hetero-nanostructures with precisely controlled semiconductor shell size and two tunable LSPRs in both visible(VIS)and near-infrared(NIR)regions associated with Au and Cu_(2-x)Se,respectively.Through systematic evaluations of the photocatalytic performance of Au@Cu_(2-x)Se upon sole NIR and dual VIS+NIR simultaneous excitations,we are capable of unambiguously elucidating the role of plasmonic coupling between two dissimilar building blocks on the accelerated photocatalytic reactions with greater rate constants from both experimental and computational perspectives.The significantly enhanced strength of the electromagnetic field arising from efficient plasmonic coupling under the excitation of two LSPRs results in the superior activities of dual plasmonic Au@Cu_(2-x)Se in photocatalysis.The new physical and chemical insights gained from this work provide the keystone for the rational design and construction of high-quality dual-or even multi-plasmonic nano-systems with optimized properties for widespread applications ranging from photocatalysis to molecular spectroscopies.

非整比锂锰尖晶石的合成与电化学性质(英文)

用流变相的方法合成了非整比锂锰尖晶石(Li1.1Mn2.1O4+y).用XRD、XPS、ICP技术对其结构和组成进行了确定;用透射电镜方法观测晶体颗粒的大小和形状.并对其电化学性质进行了研究,结果表明:该化合物作为正极材料,与整比尖晶石化合物相比,具有优良的可充电性能,初始放电容量为126mAh/g(充、放电电流密度为1mA/cm2,电压范围为4.4～3.0V),当锂片为负极时,电池进行充放电循环60次,容量衰减很少,经100次循环后,容量为117mAh/g,仅衰减7%.这一独特的性质使该化合物成为有潜力的正极材料.这一新颖的合成方法为无机材料合成提供了有效可行的途径.

Research on mechanical alloying and sintering of TiC/Ti powders

In order to improve the sintering activity of TiC which was usually added into the binder of polycrystalline diamond(PCD) and polycrystalline cubic boron nitride(PCBN),the powders of TiC and Ti mixed as molar ratio of TiC:Ti = 1:0.3 were treated by mechanical alloying.The structure and the morphology of the milled powders were analyzed by X-ray diffraction(XRD) and scan electron microscope(SEM), respectively.The milled powders were sintered by cubic hinge press.The structure of the sintered sample was analyzed by X-ray diffraction and the hardness was tested.The results showed that the grain size of the TiC and the Ti powders were decreased,as the milling time increased,and the nonstoichiometric compound of TiC_x was formed.The sintering activity of the TiC/Ti powders treated by mechanical alloying increased greatly.The hardness of the sintered sample improved from 829.2 HV for the raw powders to 2587.37 HV for the powders mechanical alloyed 20 hours.

UltrahighQ Sr_(1+x)Y_(2)O_(4+x)(x=0-0.04)microwave dielectric ceramics for temperature-stable millimeter-wave dielectric resonator antennas

Microwave dielectric ceramics should be improved to advance mobile communication technologies further.In this study,we prepared Sr_(1+x)Y_(2)O_(4+x)(x=0-0.04)ceramics with nonstoichiometric Sr^(2+)ratios based on our previously reported SrY_(2)O_(4) microwave dielectric ceramic,which has a low dielectric constant and an ultrahigh quality factor(Q value).The ceramic exhibited a 33.6% higher Q-by-frequency(Q×f)value(Q≈12,500)at x=0.02 than SrY_(2)O_(4).All Sr_(1+x)Y_(2)O_(4+x)(x=0-0.04)ceramics exhibited pure phase structures,although variations in crystal-plane spacings were observed.The ceramics are mainly composed of Sr-O,Y1-O,and Y_(2)-O octahedra,with the temperature coefficient of the resonant frequency(τ_(f))of the ceramic increasing with Y_(2)-O octahedral distortion.The ceramic comprises uniform grains with a homogeneous elemental distribution,clear grain boundaries,and no obvious cavities at x=0.02.The Sr_(1+x)Y_(2)O_(4+x)(x=0-0.04)ceramics exhibited good microwave dielectric properties,with optimal performance observed at x=0.02(dielectric constant(εr)=15.41,Q×f=112,375 GHz,and τ_(f)=-17.44 ppm/℃).The τ_(f) value was reduced to meet the temperaturestability requirements of 5G/6G communication systems by adding CaTiO_(3),with Sr_(1.02)Y_(2)O_(4.02)+2wt% CaTiO_(3) exhibiting ε_(r)=16.14,Q×f=51,004 GHz,andτf=0 ppm/℃.A dielectric resonator antenna prepared using Sr_(1.02)Y_(2)O_(4.02)+2wt%CaTiO_(3) exhibited a central frequency of 26.6 GHz,with a corresponding gain and efficiency of 3.66 dBi and 83.14%,respectively.Consequently,Sr_(1.02)Y_(2)O_(4).02-based dielectric resonator antennas are suitable for use in 5G millimeter-wave band(24.5-27.5 GHz)applications.

A-site defects in LaSrMnO_(3) perovskite-based catalyst promoting NOx storage and reduction for lean-burn exhausts

Herein,we report the high De-NOx performance of the A-site defective perovskite-based Pd/La_(0.5)Sr_(0.3)MnO_(3) catalyst.The formation of the defective perovskite structure can be proved by both the increased Mn^(4+)/Mn^(3+) ratio and serious lattice contraction due to cationic nonstoichiometry.It promotes the Sr doping into perovskite lattice and reduces the formation of the SrCO_(3) phase.Our results demonstrate that below 300℃ the A-site defective perovskite can be more efficiently regenerated than the SrCO_(3) phase as NOx storage sites due to the latter’s stronger basicity,and also exhibits the higher NO oxidation ability than the A-site stoichiometric and excessive catalysts.Both factors promote the lowtemperature De-NOx activity of the Pd/La_(0.5)Sr_(0.3)MnO_(3) catalyst through improving its NOx trapping efficiency.Nevertheless,above 300℃,the NOx reduction becomes the determinant of the De-NOx activity of the perovskite-based catalysts.A-site defects can weaken the interactions between perovskite and Pd,inducing activation of Pd sites by in-situ transformation from PdO to metallic Pd in the alternative leanburn/fuel-rich atmospheric alternations,which boosts the De-NOx activity of the Pd/La_(0.5)Sr_(0.3)MnO_(3) catalyst.The Pd/L_(0.5)Sr_(0.3)MnO_(3) catalyst exhibits the high sulfur tolerance as well.These findings provide insight into optimizing the structural properties and catalytic activities of the perovskite-based catalysts via tuning formulation,and have potential to be applied for various related catalyst systems.

Novel cemented carbide produced with TiN_(0.3) and high-entropy alloys

High-entropy alloys are suitable for use as a binder for cemented carbides duo to outstanding mechanical, oxidation and wear behavior. Therefore, high-entropy alloy was selected to replace Co and Ni metal bond in this study. The results of X-ray diffraction analysis show that CoCrNiCuMn high-entropy alloy is stabilized in the cemented carbide system. Scanning electron microscope（SEM） fractural morphologies of the cemented carbides added with CoCrNiCuMn show that CoCrNiCuMn distributes in grain boundaries, and the grains are bound tightly together. Furthermore, SEM fractural morphologies of the cemented carbides with 5 wt%, 7 wt%, and 10 wt% CoCrNiCuMn show that CoCrNiCuMn slows the growth of grains, which effectively binders the grains, prevents the generation and propagation of cracks, and finally, greatly improves the toughness of the cemented carbides.According to the results observed in the cemented carbides containing different amounts of CoCrNiCuMn, the hardness level gradually increases with the amount of CoCrNiCuMn; however, a reverse trend is seen in the toughness level. The cemented carbide with 10 wt% CoCrNiCuMn shows the highest toughness value of 7.05 MPa·m^1/2.

Effects of Ba and Ti co-doping on BiFeO3 multiferroic ceramics optimized through two-step doping

Ceramics of Bi0.9Ba0.1Fe0.925TixO3 (x = 0.0625, 0.08125, 0.0875, and 0.11) were prepared according to two doping strategies: one is called single-step doping in which Ba and Ti were doped together in calcination, while the other one is called two-step doping in which Ba and Ti were doped in calcination and sintering, respectively. Compared with samples prepared with single-step doping, those prepared with two-step doping have obviously different XRD patterns and small grains, and are dramatically improved in dielectric loss, resistivity, and remnant magnetization. A low dielectric loss of 0.05 at 10(3) Hz, a high resistivity of 4x10(12) Omega.cm, and a large remnant magnetization of 1.5 emu/g, have been obtained simultaneously for Bi0.9Ba0.1Fe0.925Ti0.11O3 prepared with two-step doping. The contrast between these two doping strategies clearly reveals the importance of establishing a proper doping strategy when two or more elements are co-doped to BiFeO3.