The h-SbxWO3+2x Oxygen Excess Antimony Tungsten Bronze

We describe the previously unreported oxygen excess hexagonal antimony tungsten bronze with composition Sb_0.5W₃O₁₀, in the following denoted as h-Sb_xWO_3+2x with x=0.167, to demonstrate its analogy to classical A_xWO₃ tungsten bronzes. This compound forms in a relatively narrow temperature range between 580 °C<T<620 °C. It was obtained as a dark-blue polycrystalline powder, and as thin, needle-shaped, blue single crystals. h-Sb_xWO_3+2x crystallizes in the hexagonal space group P6/mmm with the cell parameters a=7.4369(4) Å and c=3.7800(2) Å. The antimony and excess oxygen occupy the hexagonal channels within the network of corner-sharing WO₆ octahedra. h-Sb_xWO_3+2x has a resistivity of ρ_{300 K}≈1.28 mΩ cm at room temperature, with little if any temperature-dependence on cooling. DFT calculations on a simplified model for this compound find a metallic-like electronic structure with the Fermi level falling within rather flat bands, especially around the Γ point.     

纳米多孔双金属氧化物NiCo2O4的制备及其电化学性能

采用快速凝固与脱合金化相结合的方法制备纳米多孔Ni、Ni-Co合金,分别经腐蚀与退火获得纳米多孔NiO、NiCo_2O_4,采用XRD、SEM、TEM、N_2吸附-脱附等对多孔NiO、NiCo_2O_4电极的物相、形貌结构、孔径分布进行表征,并通过循环伏安、恒电流充放电等方法测试多孔电极的电化学性能。结果表明,得到的纳米多孔NiO具有均匀的"泥裂"式结构,在1A·g~(-1)电流密度下比电容为375 F·g~(-1),当电流密度增加至20 A·g~(-1)时的比容保持率为67.5%,在4 A·g~(-1)电流密度下循环充放电1 000次,比容保持率为81.7%;NiCo_2O_4形成典型的开放式纳米多孔双连续结构,其在1A·g~(-1)电流密度下比电容为674 F·g~(-1),当电流密度增加至20 A·g~(-1),比容保持率达72.0%;在4 A·g~(-1)电流密度下循环充放电1 000次,比容保持率达92.9%,双连续纳米多孔结构及其提供的机械稳定性,使得NiCo_2O_4表现出更为优异的超电容性能。     

Ca12[Mn19N23] and Ca133[Mn216N260]: Structural Complexity by 2D Intergrowth

Two new calcium nitridomanganates, Ca₁₂[Mn₁₉N₂₃] (P3, a=11.81341(3) Å, c=5.58975(2) Å, Z=1) and Ca₁₃₃[Mn₂₁₆N₂₆₀] ( , a=39.477(1) Å, c=5.5974(2) Å, Z=1), were obtained by a gas–solid reaction of Ca₃N₂ and Mn with N₂ at 1273 K and 1223 K, respectively. The crystal structure of Ca₁₂[Mn₁₉N₂₃] was determined from high‐resolution X‐ray synchrotron powder diffraction data, whereas single‐crystal X‐ray diffraction was employed to establish the crystal structure of the Ca₁₃₃[Mn₂₁₆N₂₆₀] phase, which classifies as a complex metallic alloy (CMA). Both crystal structures have 2D nitridomanganate layers containing similar building blocks but of different levels of structural complexity. Bonding analysis as well as magnetic susceptibility and electron spin resonance measurements revealed that only a fraction of the Mn atoms in both structures carries a localized magnetic moment, while for most Mn species the magnetism is quenched as a result of metal–metal bond formation.     

hcp‐Co Nanowires Grown on Metallic Foams as Catalysts for Fischer–Tropsch Synthesis

The Fischer–Tropsch synthesis (FTS) is a structure‐sensitive exothermic reaction that enables catalytic transformation of syngas to high quality liquid fuels. Now, monolithic cobalt‐based heterogeneous catalysts were elaborated through a wet chemistry approach that allows control over nanocrystal shape and crystallographic phase, while at the same time enables heat management. Copper and nickel foams have been employed as supports for the epitaxial growth of hcp‐Co nanowires directly from a solution containing a coordination compound of cobalt and stabilizing ligands. The Co/Cu_foam catalyst was tested for Fischer–Tropsch synthesis in a fixed‐bed reactor, showing stability and significantly superior activity and selectivity towards C5+ compared to a Co/SiO₂‐Al₂O₃ reference catalyst under the same conditions.     

Generating Metallic Amorphous Core–Shell Nanoparticles by a Solid‐State Amorphization Process

Metallic crystalline/amorphous core–shell nanoparticles consisting of a crystalline Pd core (c‐Pd) surrounded by an amorphous Fe₂₅Sc₇₅ shell (a‐FeSc) are prepared by inert‐gas condensation. A phase transformation of the c‐Pd by a solid‐state diffusion process resulting in an amorphous core (a‐PdSc) surrounded by an amorphous FeSc shell is observed if the core–shell structure is irradiated at ambient temperature with 300 keV electrons. The amorphization process seems to involve the diffusion of irradiation‐induced defects and is presumably driven by the large negative heat of mixing of Pd and Sc, as well as by the excess enthalpy of the interfaces between the c‐Pd regions and the surrounding a‐FeSc. The structural transformation reported here opens a new way to producing metallic amorphous core–shell nanoparticles of different chemical compositions and probably novel properties.     

Surface shape resonances of ridges on a thin film

The spectrum of surface shape resonances associated with a finite number of ridges on one interface of an otherwise plane film is calculated. The frequencies are obtained numerically by solving the homogeneous integral equations which describe the electrostatic field in the vicinity of a surface defect. The calculations are performed for a surface with ridges with Gaussian, Lorentzian and sinusoidal profiles. The results show a strong dependence of the localized plasmon frequencies on the surface profile, on the distance between the ridges, and on the thickness of the film. Received 5 April 1999 and Received in final form 6 July 1999     

动力飞行体电磁脉冲效应数值分析

 利用时域有限差分方法模拟了在不考虑等离子体高温尾焰情况下,电磁脉冲与动力飞行体的相互作用。计算结果表明：在入射电磁脉冲的作用下, 飞行体蒙皮上将感应很大的皮电流; 感应电流密度的波形为衰减振铃信号波形,振铃周期等于电流波在整个飞行体长度上流动两次的时间;感应皮电流密度分布的特点是飞行体两端电流密度小,中部大。     

有尾焰动力飞行体电磁脉冲效应数值分析

 利用时域有限差分方法分析了动力段飞行体的等离子体高温尾焰对飞行体电磁脉冲效应的影响。计算结果表明：尾焰的存在极大地改变了飞行体蒙皮上感应电流密度的波形及分布;带尾焰飞行体感应皮电流密度不同于无尾焰时的情况;飞行体蒙皮感应电流密度的波形为衰减振铃信号波形,振铃周期等于电流波在整个飞行体和尾焰长度上流动两次的时间。     

纳米晶Si在高压下的电学性质与金属化相变

 在金刚石压砧装置上,采用电阻和电容测量方法,研究了粒径为15~18 nm和80 nm的纳米晶Si在室温下、24 GPa内的电阻、电容与压力的关系。实验结果表明,它们分别在19~17 GPa和14 GPa左右发生了金属化相变。