Doping golden clusters: MAu19 and M2Au18 (M = Cu and Na)

The structural and electronic properties of MAu⁻₁₉ and M₂Au⁻₁₈ (M = Cu and Na) have been studied by the relativistic density-functional calculations. It is found that the most stable configurations of CuAu⁻₁₉ and Cu₂Au⁻₁₈ are the face-centered and two-face-centered doped structures based upon the tetrahedral structure Au⁻₂₀. In contrast, the ground states of Na-doped gold clusters (NaAu⁻₁₉ and Na₂Au⁻₁₈) exhibit flat-cage configurations. The PES of these ground states are depicted that may be helpful to identify their configurations in the future experiments. The face-centered and two-face-centered doped tetrahedral structures of CuAu⁻₁₉ and Cu₂Au⁻₁₈ have a large HOMO–LUMO gap, indicating that they are chemically stable.     

Note on One-Dimensional Lattice Gas in External Fields

Abstract

The fundamental equations of the scaled particle theory are derived for a one-dimensional lattice gas in an external potential. These equations relate the work required to add a particle, at a fixed point, to a N – 1 particle system to the activity and to a series of coordinate distribution functions. The equations hold in any dimension, and replacing sums by integrals, describe continuum fluids. The rigid lattice gas is solved by these means. When nearest neighbors interact, in a positive, increasing external potential, a formal solution is obtained by a matrix method. The grand partition function, in the infinite length limit, depends only on a single eigenvalue of an infinite product of matrices. The one-particle distribution, in this limit, is reduced to a series of terminating continued fractions, which is readily approximated in the high coordinate or low activity limit. Lastly, it is shown that the zeros of the grand partition function lie on the negative real axis of the complex activity plane when the nearest-neighbor interaction is positive.     

Tap study of the impact of the oxidation state of Pt/PrCeZrO and Pt/GdCeZrO catalysts on their reactivity in the partial/deep oxidation of methane

The temporal analysis of products (TAP) technique coupled with the oxygen TPD was used to elucidate the effects of the Pt-supported fluorite-like doped ceria–zirconia oxide chemical composition and the type of pretreatment on their oxygen bonding strength, mobility, and reactivity as related to catalytic properties in the partial oxidation of methane into synthesis gas. A rapid evolution of hydrogen under CH₄ pulse observed for oxidized catalysts agrees with the direct route of the methane selective oxidation into syngas. This route is favored by the Pt-support interaction and a moderate bonding strength of surface oxygen species along with a high lattice oxygen mobility.     

Direct Pyrolysis of Molybdophosphate-based Ionic Salt for One-step Synthesis of N,P Co-doped Carbon/MoO3-x Hybrids with Superior Lithium Storage Performance

N, P co-doped carbon/MoO3-x hybrids(NPC/MoO3-x) were synthesized via one-step pyrolysis of molybdophosphate-based ionic salt precursor. Doped carbon and oxygen vacancies(OVs) were synchronously introduced into the NPC/MoO3-x hybrids without any other redundant procedure. As anodes for lithium-ion batteries, the NPC/MoO3-x hybrids delivered a high initial Coulombic efficiency(ICE) of 81% as well as high charge capacity of 516 mA·h/g after 100 cycles at 1 A/g, indicating the excellent reversibility and rate capability. The enhanced lithium storage performance was attributed to the rational combination of surface engineering and OVs, which is beneficial to the more active sites and fast ionic/electronic transport.     

Microstructural studies of bulk and thin film GDC

Ceria rare earth solid solutions are known as solid electrolyte with potential application in oxygen sensors and solid oxide fuel cells. We report the preparation of gadolinia-doped ceria, Ce_0.90Gd_0.10O_1.95, by the conventional solid-state reaction method and the preparation of thin films from a sintered pellet of gadolinia-doped ceria by the pulsed laser deposition technique. The effect of process conditions, such as substrate temperature, oxygen partial pressure, and laser energy on microstructural properties of these films are examined using powder X-ray diffraction, scanning electron microscopy, atomic force microscopy, and Raman spectroscopy.     

Effect of steady-state conditions on self-pulsing characteristics of Yb-doped cw fiber lasers

Fiber laser resonator configurations have been analyzed theoretically on the basis of steady-state rate equations to optimize the laser conversion efficiency. Evolution of the pump- and signal powers and the saturated gain coefficient along the length of the laser medium has been simulated for high- and low-finesse resonators in forward- and backward pumping schemes. The corresponding fiber laser configurations have been setup to verify the results of simulation. Backward pumping configuration in an Yb-doped fiber laser has been found to be the most efficient, and in this configuration a maximum cw output power of 10.75 W in single transverse mode with an optical-to-optical conversion efficiency of 62.5% has been achieved. The laser output spectrum was peaked at 1093 nm with full-width at half-maximum (FWHM) line-width of about 9 nm. In the low-finesse resonator configuration, it has been found that experimental observations differ from theoretical simulation results. In this case, output power from both ends ceases to increase linearly beyond 1.8 W, and starts fluctuating due to the onset of strong random self-pulsing phenomenon. Our investigation shows that a non-uniform steady-state gain along the fiber length facilitates the self-pulsing process.     

Mixed metal fluorides as doped Lewis acidic catalyst systems: a comparative study involving novel high surface area metal fluorides

MF₃-doped/MgF₂ systems with enhanced Lewis acidity are reported, which are obtained either by the conventional aqueous route of co-precipitation or, by a novel non-aqueous soft chemistry route. The latter gives outstanding high surface areas and exhibits potent Lewis acid catalyst behaviour. The doped solid metal fluorides with dopant metals such as Ga, In, Fe, V are discussed in terms of the modified Tanabe model, which is adopted for metal fluoride systems. The two doped but differently prepared systems are analysed according to their surface characteristics by BET surface area, pore-size distribution and XPS/XAES as well as for the solid state structure by scanning electron microscopy (SEM), XRD and -MAS-NMR. The surface properties were evaluated by photoacoustic IR-spectroscopy of pyridine adsorbates and selected catalytic reactions.The exemplarily investigated GaF₃-doped/MgF₂ system reveals modified intrinsic properties of the solid mixture culminating in very high surface areas of a structurally distorted mesoporous solid and electrostatic charge rearrangements causing increased Lewis acid sites.     

Nano-ionic thin films of gadolinia-doped ceria prepared by pulsed laser ablation

Microstructural properties of nano-ionic thin films of gadolinia-doped ceria (GDC) prepared by pulsed laser ablation from sintered targets of gadolinia (5–20 mol%) doped ceria are investigated. The ionic conductivity measurements of the sintered pellets showed a decrease in the activation energy from 1.1 to 0.65 eV for 5 and 30 mol% gadolinia-doped ceria, respectively. The microstructural properties of the GDC films as a function of substrate temperature, oxygen partial pressure, and laser energy show that the films are polycrystalline in the entire range of substrate temperature. The grain size is found to increase with increasing temperature up to 873 K. Further improved crystallinity is noticed for the films grown with oxygen partial pressure of 0.1–0.2 mbar. X-ray diffraction and transmission electron microscopy (TEM) reveal nanocrystalline grains with textured growth along <111> orientation in these films at low substrate temperature and at lower oxygen partial pressure. TEM study shows a uniform distribution of nanocrystal of 8–10 nm for energies ≤200 mJ/pulse, and nanocrystals embedded in a large crystalline matrix of doped ceria for energies in the range 400–600 mJ/pulse. Raman spectroscopy also confirms the defects in these films. The study also reveals that the substrate temperature and oxygen partial pressure could influence preferred orientation, while the laser energy could significantly influence defect concentration in these films. Invited paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, Dec. 7–9, 2006.     

铝掺杂锰酸锂正极材料制备及第一性原理研究

采用固相法制备出高纯度纳米LiAl0.25Mn1.75O4并用此制备成了半电池,对其进行充放电循环测试和阻抗测试,并与原始LiMn2O4的测试结果相比较。另采用基于密度泛函理论的第一原理方法,研究了掺铝锰酸锂LiAl0.25Mn1.75O4的能带结构、态密度和原子布居,实验与计算分析结果表明LiAl0.25Mn1.75O4在室温下0.01C放电时首次放电容量为124.8mAh/h,室温0.2C下50个循环周期后放电比容量保持率可达到83.6%;LiAl0.25Mn1.75O4的能带带隙为0.21eV,分态密度中Al-s轨道与O-s轨道在-20eV左右的明显杂化,均表明LiAl0.25Mn1.75O4材料具有高导电率、高结构稳定性、高比容量保持率的性能,这为推动锂离子电池锰酸锂正极材料的发展提供理论依据。     

Comparative study for N and S doped carbon dots: Synthesis,characterization and applications for Fe probe and cellular imaging

A facile and eco-friendly approach to prepare nitrogen(N)- and sulfur(S)-doped carbon dots (CDs) by one step microwave-assisted pyrolysis of the precursors with dl-malic acid as carbon source, ethanolamine and ethane-sulfonic acid as N and S dopants, respectively, was reported. Through the extensive investigation on morphology, chemical structures and optical properties of the carbon dots, it was found that the obtained CDs exhibited good luminescence stability, high resistance to photo bleaching and favorite solubility. Compared with undoped CDs, adding the N or S dopant could give rise to a slightly smaller particle size and a long fluorescence lifetime of CDs. Moreover, the optimal N-CDs was successfully employed as good multicolor cell imaging probes due to its fine dispersion in water, excitation-dependent emission, excellent biocompatibility and low toxicity. Besides, such N-CDs showed a wide detection range and excellent accuracy as fluorescent probe for Fe³⁺ ions. This probe enabled the selective detection of Fe³⁺ ions with a linear range of 6.0–200 μM and a limit of detection of 0.80 μM.