Mg-doped layered oxide cathode for Na-ion batteries

Na-ion batteries (NIBs) are regarding as the optimum complement for Li-ion batteries along with the rapid development of stationary energy storage systems. In order to meet the commercial demands of cathodes for NIBs, O3-type Cu containing layered oxide Na_0.90Cu_0.22Fe_0.30Mn_0.48O₂ with good comprehensive performance and low-cost element components is very promising for the practical use. However, only part of the Cu³⁺/Cu²⁺ redox couple participated in the redox reaction, thus impairing the specific capacity of the cathode materials. Herein, Mg²⁺-doped O3-Na_0.90Mg_0.08Cu_0.22Fe_0.30Mn_0.40O₂ layered oxide without Mn³⁺ was synthesized successfully, which exhibited improved reversible specific capacity of 118 mAh/g in the voltage range of 2.4-4.0 V at 0.2 C, corresponding to the intercalation/deintercalation of 0.47 Na⁺ (0.1 more than that of Na_0.90Cu_0.22Fe_0.30Mn_0.48O₂). This work demonstrates an important strategy to obtain advanced layered oxide cathodes for NIBs.     

Structural and electrochemical study of Cr-substituted layered manganese oxide cathode materials

A lithiated layered Mn–Cr compound, Li[Cr_0.29Li_0.24Mn_0.47]O₂ was synthesized by a solution method with subsequent quenching. The crystal structure was investigated by X-ray diffraction (Rietveld refinement) and Electron diffraction showing co-existence of rhombohedral and monoclinic structures. According to the co-indexed electron diffraction patterns and HRTEM images, Li[Cr_0.29Li_0.24Mn_0.47]O₂ electrode was composed of nano-scale domains indexed in monoclinic and hexagonal structures, simultaneously. The nano-composite cathode successfully prevents spinel-like structural transformation during cycling and delivered a good reversible capacity of about 195 mAh/g between 2.4 and 4.7 V.     

Polyol synthesis of polycrystalline cuprous oxide nanoribbons and their growth chemistry

A facile organic-solution method was developed for the synthesis of two-dimensional cuprous nanostructures. Ribbons as thin as 50 nm were successfully prepared by dissolving CuCl in ethylene glycol before raising the solution temperature to 150°C in air. Transmission electron microscopic studies revealed that the ribbon nanostructures obtained were polycrystalline, with nanocrystals present in the structures mostly less than 25 nm. Selective-area electron diffraction patterns taken from the ribbon nanostructures indicated that the chemical composition of the nanocrystals was Cu₂O, though X-ray photoelectron spectrometric analysis showed that the nanostructures also contained the Cu²⁺ phase. Growth factors including the molecular structure of the solvent and the counter-ion of copper in the precursor that may affect the formation of polycrystalline nanoribbons were examined. More importantly, the detail of chemistry involved in the step-by-step, dimensional growth of copper-based nanostructures in ethylene glycol is presented at the molecular level for the first time using the growth of the Cu₂O nanoribbon as an example. Ethylene glycol chelates Cu²⁺, which is produced from Cu⁺ undergoing disproportionation reactions, to form tetragonally elongated glycolates. A sequence of nucleophilic substitutions then takes place to bond glycolates together to yield stripe-like polymers before the polymers aggregate via van der Waals force into ribbon nanostructures. The Cu⁰ produced from the disproportionation reaction is crystallized out within the polymers and oxidized at elevated temperature by the dissolved O₂ in the solution to form Cu₂O nanocrystals.     

Age-induced oxide on cleaved surface of layered GaSe single crystals

It is shown that a long-term keeping of a layered gallium monoselenide at room temperature results in formation of the intrinsic oxide at a cleaved surface of semiconductor. It is found that the chemical compositions of the intrinsic oxide at the surfaces of the intentionally undoped and doped samples of GaSe are different. The electrical properties of the GaSe-intrinsic oxide system are presented. It is established that intrinsic oxide films at the surface of GaSe are characterized by current instability with N-type current-voltage characteristic. The influence of relative humidity on changes of capacitance and surface resistivity of the intrinsic oxide is also discussed.     

Influence of a thin surface layer on light scattering by spherical particles

The Mie problem with modified boundary conditions that take into account the influence of a thin surface layer on the scattering of an electromagnetic wave by a spherical particle is considered. Analytical equations are derived for the partial amplitudes of scattered waves and forced oscillations. These equations are applicable in the case of anisotropy and gyrotropy of an optical response from the surface layer.     

Dynamics of spherical particles on a surface: collision-induced sliding and other effects

We present a model for the motion of hard spherical particles on a two-dimensional surface. The model includes both the interaction between the particles via collisions and the interaction of the particles with the substrate. We analyze in detail the effects of sliding and rolling friction, which are usually overlooked. It is found that the properties of this particulate system are influenced significantly by the substrate-particle interactions. In particular, sliding of the particles relative to the substrate after a collision leads to considerable energy loss for common experimental conditions. The presented results provide a basis that can be used to realistically model the dynamical properties of the system, and provide further insight into density fluctuations and related phenomena of clustering and structure formation.     

The recoilless fraction of the oxide surface layer formed on small iron particles

Small iron particles with oxide surface layer were studied by Mössbauer Spectroscopy at various temperatures in the range of 5K to 300K. The Debye temperature of the oxide layer and the temperature dependence of f2/f1 were obtained, where f1 and f2 are the recoilless fractions for the inner α-iron core and the oxide layer respectively. Furthermore, the method of estimating the thickness of the oxide layer was improved.     

Changes in surface chemistry of an Ir---W mixed metal coated cathode during activation

A comparative study has been made between a mixed metal (60% Ir-40%W) coated cathode and a “B” cathode during activation and also in their respective steady states. The rate limiting factor in the activation of the coated cathode is the oxidation of the initial Ba type surface to a BaO type surface. Since on the “B” cathode Ba and O emerge together, its activation is faster than the coated cathode. In the steady state of operation, both cathodes exhibit a surface near BaO stoichiometry which is the optimum composition for the minimum work function. This work function is about 0.2 eV lower on the coated cathode than on the “B” cathode. An accelerated life test at 1575 K indicated a gradual decrease of the Ir concentration in the coating.     

Emissive properties of silver particles at silver oxide surface defects

The absorption and fluorescence properties of pure silver and silver oxide model systems have been explored using ab initio linear response methods in context of the observed fluorescence by photoactivation of thin silver oxide films. Silver clusters interacting with F-center defects created from silver oxide surfaces as well as silver clusters interacting directly with the silver oxide surface are good candidates for emissive centers giving rise to fluorescence in the visible regime. These findings represent a starting point towards conceptual understanding of emissive silver cluster-support properties, which might be important for the development of optical storage media with large data capacities. PACS 31.15.Qg; 31.15.Ar     

Novel layered perovskite GdBaCuFeO5+x as a potential cathode for proton-conducting solid oxide fuel cells

A layered perovskite GdBaCuFeO_5+x (GBCuF) was developed as a cathode material for intermediate-temperature solid oxide fuel cells based on a proton-conducting electrolyte of stable BaZr_0.1Ce_0.7Y_0.2O_3?δ (BZCY). The X-ray diffraction results showed that GBCuF was chemically compatible with BZCY after co-fired at 1,000 °C for 10 h. The thermal expansion coefficient of GBCuF, which showed a reasonably reduced value (15.1?×?10^?6 K^?1), was much closer to that of BZCY than the cobalt-containing conductor. The button cells of Ni–BZCY/BZCY/GBCuF were fabricated and tested from 500 to 700 °C with humidified H₂ (～3 % H₂O) as a fuel and ambient oxygen as the oxidant. A high open-circuit potential of 1.04 V, maximum power density of 414 mW cm^?2, and a low electrode polarization resistance of 0.21 Ω cm² were achieved at 700 °C, with calculated activation energy (E _a) of 128 kJ mol^?1 for the GBCuF cathode. The experimental results indicated that the layered perovskite GBCuF is a good candidate for cathode material.     

Detection of organic substances adsorbed on the surface of spherical particles from light scattering characteristics by scanning flow cytometry

The possibility of using scanning flow cytometry to determine the size and refractive index of individual particles having an internal structure is demonstrated. In particular, for aqueous suspensions of polystyrene latexes adsorbing dissolved humic acids, it is shown experimentally and theoretically that the method of scanning flow cytometry is capable of rapid and high-accuracy determination of the increase in the size and the decrease in the effective refractive index of such particles in comparison with latexes whose surface is free from humic acids.     

A Mössbauer study of spin-pinning in the oxide surface layer on fine iron particles

Fine α-Fe particles coated with an oxide surface layer were prepared by the evaporation technique. The spin pinning in the oxide surface layer were studied by means of the Mössbauer effect in an applied field of 6T during a thermal-cycle process. The anisotropy energy on the surface was estimated.     

Influence of inhomogeneous exchange interaction on the moments of the ferromagnetic resonance lines in polycrystalline ferrites

From the viewpoint of the spin-wave approach to the theory of ferromagnetic resonance, the first four moments of the absorption line are calculated in this paper. It is shown that in addition to the magnetic dipole-dipole interaction, the inhomogeneous exchange interaction which has been neglected in previous papers exerts substantial influence on the asymmetry and peakedness of the ferromagnetic resonance line.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 75–78, July, 1979.     

磁场对球头阴极二极管特性的影响

 采用全电磁PIC粒子模拟方法研究了磁场对球头阴极二极管物理特性的影响。结果表明外加磁场主要是通过对二极管束流轨迹的改变来影响二极管的物理特性。由于外加磁场将约束其产生电子束的发散，结果使其空间电荷限制电流减小，其值在无外加磁场并且自磁场可以忽略时的空间电荷限制电流值的0.5~1倍范围内。当外加磁场足够强时，束流轨迹主要受外加磁场控制，二极管产生的电子束既不箍缩也不发散。强外加磁场条件下的空间电荷限制电流近似为无外加磁场时的一半；在无外加磁场条件下，在阳极处的束流半径随二极管电压电流的增大而减小，空间电荷限制电流增强因子随束流半径的减小而减小，随二极管电压电流增大而减小。这一系列结果是在二极管电流小于其自箍缩临界电流条件下得到的。     

Change in activation energy of surface conduction in polycrystalline zinc oxide upon irradiation by electrons

The dependence of activation energy E_A of surface conduction _s in polycrystalline ZnO upon dosage of irradiation by electrons with energy of 30 keV is studied. It is found that the function _s = f(T) is composed of three segments with E_A values in unirradiated ZnO approximately equal to 0.77, 0.12, and 0.048 eV, which are ascribed to a surface potential barrier between the powder crystallites and donor levels of interstitial Zn⁺ _i and Zn^o _i atoms, respectively. With increase in radiation dosage E_A decreases on all segments, which is explainable by reduction in with increase in the concentrations of Zn⁺ _i and Zn^o _i due to radiation desorption and lattice radiolysis.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 94–97, July, 1984.     

Competitive segregation of impurities on the surface of polycrystalline copper

The competitive segregation of sulfur, carbon, and phosphorus on the surface of polycrystalline copper and the segregation kinetics of sulfur in the temperature range 675–875 K have been investigated by Auger electron spectroscopy. The equilibrium segregation energies of impurities and the sulfur diffusion parameters in the near-surface region of copper with a thickness d ≤ 5 μm have been calculated on the basis of the experimental data.     

Acetic acid decomposition on a polycrystalline platinum surface

The decomposition of CH¹³₃COOH on a polycrystalline platinum surface has been examined at temperatures between 300 and 900 K during continuous exposure to CH¹³₃COOH at 7×10^-4 Torr. On an initially clean platinum surface ¹³CO, CO, ¹³CO₂, H₂ and adsorbed carbon-12 are the major reaction products. The adsorbed carbon eventually poisons completely the reactions that produce these products. For temperatures above approximately 800 K, the carbon overlayer that is formed is graphitic and saturates at a carbon adatom concentration of (2.6-3.5)×10¹⁵ cm^-2. The reaction quantities of ¹³CO and ¹³CO₂ that are produced depend both on the surface temperature and the carbon coverage. Lower temperatures and higher carbon coverages favor the production of ¹³CO. On the graphitized platinum surface, the catalytic dehydration of acetic acid to ketene and water proceeds at steady-state.