Chemical Reactivity of Tetrasulfur Tetranitride: Synthesis,Physical Properties,and Structural Characterization of the Amorphous Phase Cu7S4N4

Tetrasulfur tetranitride, S₄N₄, reacts with elemental Cu within inert solvents to a black‐blue material of approximate composition Cu₇S₄N₄ which is totally amorphous to X‐rays and which cannot be made crystalline by either thermal treatment or electron radiation. Cu₇S₄N₄ explodes if heated above 234 °C or when subjected to mechanical shock to eventually yield copper(I) sulfide; this together with the characteristic infrared spectrum of Cu₇S₄N₄ indicates the presence of molecular S₄N₄ units inside the amorphous phase. The metastable nature of Cu₇S₄N₄ is also mirrored by electron microscopy which furthermore allows the structural characterization of its degradation products. Based on experimental EXAFS data offering characteristic Cu—N and Cu—S distances, a theoretical crystalline approximant of Cu₇S₄N₄ was suggested and structurally optimized by density‐functional total‐energy calculations including periodic boundary conditions. This model incorporates a central S₄N₄ unit bonded to three shells of Cu atoms of different functionalities; in addition, a partial rupture of the S₄N₄ unit is likely to allow for a lowering of the total energy of the metastable phase. The latter observation supports the impossibility to make Cu₇S₄N₄ crystallize using ₄N₄ crystallize using whatever kind of measures.     

Collocation Methods for Weakly Singular Second-kind Volterra Integral Equations with Non-smooth Solution

Collocation type methods are studied for the numerical solutionof the weakly singular Volterra integral equation of the secondkind: where the solution (t) is assumedto have the form f(t) = x(t)+r^?(t), x and being sufficientlysmooth. The solution is approximated near zero by a linear combinationof powers of t?, and away from zero by the usual polynomialrepresentation. Convergence is proved and many numerical experimentsare carried out with examples from the literature. A comparisonis made with a method of Brunner & Norsett (1981), originallydeveloped for (1) with a smooth solution. Special attentionis paid to the numerical approximation of the so-called momentintegrals which emerge in the collocation scheme.     

An interface clusters mixture model for the structure of amorphous silicon monoxide (SiO)

The present state of research on the structure of amorphous silicon monoxide (SiO) is reviewed. The black, coal-like modification of bulk SiO is studied by a combination of diffraction, microscopy, spectroscopy, and magnetometry methods. Partial radial distribution functions of SiO are obtained by X-ray, neutron and electron diffraction. Disproportionation of SiO into Si and SiO₂ is verified. High resolution TEM gives an upper limit of less than 2 nm for the typical Si cluster size. The Si K-edge electron energy-loss near-edge structure (ELNES) data of SiO are interpreted in terms of the oxidation states Si⁴⁺ and Si⁰. X-ray photoelectron spectroscopy gives first details about possible stoichiometric inhomogeneities related to internal interfaces. The wipe-out effect in the ²⁹Si MAS NMR signal of SiO is confirmed experimentally. The new estimation of the wipe-out radius is about 1.1 nm. First-time W-band, Q-band, and X-band ESR and SQUID measurements indicate an interfacial defect structure. Frequency distributions of atomic nearest-neighbours are derived. The interface clusters mixture model (ICM model) suggested here describes the SiO structure as a disproportionation in the initial state. The model implies clusters of silicon dioxide and clusters of silicon surrounded by a sub-oxide matrix that is comparable to the well-known thin Si/SiO₂ interface and significant in the volume because of small cluster sizes.     

无机酸洗脱对胜利褐煤微晶结构及其自燃倾向性的影响

利用XRD、Raman、XPS和FT-IR表征技术,研究无机酸洗脱(HCl、H2SO4、HCl-HF)处理的胜利褐煤微晶结构的变化,采用自行设计的表面吸附仪-GC联用装置,对样品进行不同温度的低温脉冲氧化实验,考察了煤样在不同温度下氧吸附量的变化规律,通过低温脉冲氧吸附规律与TG/DTG和固定床燃烧实验关联,考察了煤样的自燃倾向。结果表明,无机酸洗脱对矿物质的脱除使得煤结构的有序度增加,石墨化程度提高,无机酸洗脱煤样与原煤相比吸氧量明显下降。随着吸附温度的升高,各煤样吸氧量明显增加,且随着脱除矿物质程度的增加,吸氧量呈减小的趋势,导致自燃倾向降低。     

Electronic structure of (LaSr)2CuO4 and (NdCe)2CuO4

The electronic structure of (LaSr)₂CuO₄ and (NdCe)₂CuO₄ are compared. It is concluded that in both materials after doping by holes and electrons respectively the Fermi energy is at the top of the valence band. This explains many symmetrical properties and in particular the photoemission experiments.Dedicated to Prof. P. Kienle on the occasion of his 60th birthday     

An approximate treatment of scattering based on the delta boundary operator

The development of a scheme to treat two-dimensional electromagneticscattering by electrically large, perfectly conducting bodiesis described. It incorporates the effects of surface curvatureand non-local phenomena and has the potential to provide thebasis for a general technique yielding more accurate predictionsthan the widely used physical optics method.     

Structural,compositional, optical and colorimetric characterization of TiN-nanoparticles

With the construction of novel XUV sources, such as VUV FELs, XUV laser-matter interaction will become available at ultra-high intensities. But even tabletop facilities such as XUV lasers or High Harmonic Generation, are starting to reach intensities high enough to produce dense plasmas. XUV laser-matter interaction is studied by a 1D hydrodynamic Lagrangian code with radiative transfer for a range of interesting XUV sources. Heating is found to be very different for Z = 12-14 elements having L-edges around the XUV laser wavelength. Possible absorption mechanisms were investigated in order to explain this behaviour, and interaction with cold dense matter proved to be dominant. Plasma sensitivity to XUV laser parameters such as energy, pulse duration, and wavelength was also studied, covering ranges of existing XUV lasers. We found that XUV laser-produced plasmas could be studied using tabletop lasers, paving the way for future VUV-FEL high intensity experiments.Received: 6 December 2003, Published online: 20 January 2004PACS: 52.38.Dx Laser light absorption in plasmas (collisional, parametric, etc.) - 52.65.Kj Magnetohydrodynamic and fluid equation - 42.55.Vc X- and gamma-ray lasers     

Novel nanoparticle matter: ZrN-nanoparticles

This work presents the results of the first preparation (to the best of current knowledge) and investigation of ZrN nanoparticles. The particles were produced by laser ablation/evaporation and adiabatic expansion from zirconium nitride powder targets. The particle size could be varied by applying different seeding gas flows. The size distributions were fairly narrow with mean diameters from 2R=5.5 nm to 2R=6.5 nm. Compositional analysis by secondary ion mass spectrometry (SIMS) and transmission electron microscopy (TEM) revealed, that almost stoichiometric crystalline particles were formed. The in-situ optical transmission spectroscopy measurements yielded a single plasmon resonance in the visible spectrum. PACS 81.07.-b; 78.67.-n     

Long-term structural surface modifications of mixed conducting La<Subscript>2</Subscript>NiO<Subscript>4+δ</Subscript> at high temperatures

Abstract  Long-term annealing of La₂NiO_4+δ single crystals at 1,273 K in air leads to the formation of nickel-rich Ruddlesden–Popper phases at the single-crystal surfaces. Both the composition and the morphology of these phases depend on the surface orientation; whereas only crystallites of La₄Ni₃O_10−δ were observed on (001) surfaces, both La₃Ni₂O_7−δ and La₄Ni₃O_10−δ were formed on (100) surfaces. The formation of the nickel-rich RP phases is believed to be due to surface segregation of nickel or evaporation of a volatile lanthanum species. The crystallographic (001) planes inside the La₃Ni₂O_7−δ and La₄Ni₃O_10−δ crystallites were found to be oriented in the direction of preferential crystallite growth, which indicates that the diffusion of lanthanum and nickel cations is faster along the crystallographic (001) planes than perpendicular to these planes. Graphical abstract