Stable SiOC/Sn Nanocomposite Anodes for Lithium‐Ion Batteries with Outstanding Cycling Stability

Silicon oxycarbide/tin nanocomposites (SiOC/Sn) are prepared by chemical modification of polysilsesquioxane Wacker‐Belsil PMS MK (SiOC_MK) and polysiloxane Polyramic RD‐684a (SiOC_RD) with tin(II)acetate and subsequent pyrolysis at 1000 °C. The obtained samples consist of an amorphous SiOC matrix and in‐situ formed metallic Sn precipitates. Galvanostatic cycling of both composites demonstrate a first cycle reversible capacity of 566 mAhg^?1 for SiOC_MK/Sn and 651 mAhg^?1 for SiOC_RD/Sn. The superior cycling stability and rate capability of SiOC_RD/Sn as compared to SiOC_MK/Sn is attributed to the soft, carbon‐rich SiOC matrix derived from the RD‐684a polymer, which accommodates the Sn‐related volume changes during Li‐uptake and release. The poor cycling stability found for SiOC_MK/Sn relates to mechanical failure of the rather stiff and fragile, carbon‐poor matrix produced from PMS MK. Incremental capacity measurements outline different final Li–Sn alloy stages, depending on the matrix. For SiOC_RD/Sn, alloying up to Li₇Sn₂ is registered, whereas for SiOC_MK/Sn Li₂₂Sn₅ stoichiometry is reached. The suppression of Li₂₂Sn₅ phase in SiOC_RD/Sn is rationalized by an expansion restriction of the matrix and thus prevention of a higher Li content in the alloy. For SiOC_MK/Sn on the contrary, the matrix severely ruptures, providing an unlimited free volume for expansion and thus formation of Li₂₂Sn₅ phase.     

Green Emission in Ladder‐Type Quarterphenyl: Beyond the Fluorenone‐Defect

In polyfluorenes it is generally accepted that (photo)degradation leads to fluorenone type defects that accept the excitation energy and emit green‐to‐yellow light with rather low efficiency. Although initial spectroscopic studies suggest the same to hold true for ladder‐type poly(para‐phenylene)s (LPPPs), kinetic studies of the degradation process are not compatible with the established mechanism. In general, the observed green emission can be caused by the introduction of carbonyl groups; however, only if associated with an additional disruption of the backbone rigidity and hence planarity of the entire π‐system. This is clearly shown by comparison with synthesized model compounds, which are bearing the fluorenone motif yet possess very different optical properties as compared to the defects, which are actually formed. Degradation can be caused by solvent specific, yet substrate nonspecific aromatic formylation but mainly originates from reaction with in‐situ generated singlet oxygen, both in solution as well as in thin films. Time‐dependent photoluminescence measurements on thin films show that green emission is enhanced by energy transfer from intact molecules to defect centers.     

Fabrication and Spatially Resolved Functionalization of 3D Microstructures via Multiphoton‐Induced Diels–Alder Chemistry

Three‐dimensional microstructures are fabricated utilizing direct laser writing combined with a non‐radical step polymerization based on multiphoton‐induced Diels–Alder chemistry of o‐quinodimethanes and maleimides. Woodpile photonic crystals with a total of five axial periods and a rod spacing of down to 500 nm are fabricated. The structures are characterized via scanning electron microscopy and focused ion beam milling. In addition, corresponding photonic stop bands are investigated via light microscopy as well as transmission and reflection spectroscopy. The Diels–Alder based network formation during direct laser writing is verified via infrared spectroscopy. Spatially resolved surface patterning of covalently bonded functional molecules on fabricated structures is demonstrated by employing the direct laser writing setup and a bromine containing maleimide. The successful surface modification is verified via time‐of‐flight secondary ion mass spectrometry.     

Simplification orderings: Putting them to the test

Various methods for proving the termination of term rewriting systems have been suggested. Most of them are based on the notion of a simplification ordering. In this paper, a collection of well-known simplification orderings will be briefly presented including path orderings and decomposition orderings. A satisfactory application to examples often found in practice is an essential requirement concerning such orderings. We describe a detailed empirical study of their time complexities with respect to comparable pairs of terms.This research was supported by the Deutsche Forschungsgemeinschaft, SFB 314 (D4-Projekt).     

Thermodynamic investigation of the austenite and the delta ferrite in the system Fe-Cr-Mn-N

The nitrogen solubility was measured in a wide range of temperatures including both the austenitic and the ferritic phase of iron-chromium-manganese alloys. The mass contents of the samples were 6.0 to 20.5 % Cr and 5.7 to 16.6 % Mn. Parameters describing the austenite and the delta ferrite in the system Fe-Cr-Mn-N were calculated analyzing all available experimental data. This evaluation yielded an improvement of the known parameters describing the austenitic phase by means of the regular solution model. At the first time, accurate thermodynamic parameters describing the delta phase both in the systems Fe-Mn-N and Fe-Cr-Mn-N could be deduced. By means of the phase diagram program package PD-pp the austenite-delta ferrite phase boundaries of the investigated alloys were calculated. They were compared with experimentally determined temperatures and nitrogen concentrations in the two-phase region. There is a good correspondence between theory and experiment. Using published data describing the melt a calculation of phase diagrams in the high temperature region can be performed.     

Thermodynamic calculation of phase diagrams in the iron-nitrogen system

On the basis of recent measurements of the equilibria between N₂ and NH₃ containing gas atmospheres, respectively, and of the nitrogen solved in the α, γ and ε iron phases a thermodynamic analysis of the Fe—N system has been carried out. The Gibbs free energy of the γ, ε transformation of pure iron was derived. The composition Fe_4.3N was calculated concerning the γ’ phase above 593°C. The phase boundaries were stated as temperature functions of the N₂ equilibrium pressures. The resulting phase diagram shows the stability regions of the α, γ, γ’ and ε phases and an α/γ/ε triple point which corresponds to that of the pure iron.     

Structure and catalytic reactivity of Rh oxides

Using a combination of experimental and theoretical techniques, we show that a thin RhO₂ surface oxide film forms prior to the bulk Rh₂O₃ corundum oxide on all close-packed single crystal Rh surfaces. Based on previous reports, we argue that the RhO₂ surface oxide also forms on vicinal Rh surfaces as well as on Rh nanoparticles. The detailed structure of this film was previously determined using UHV based techniques and density functional theory. In the present paper, we also examine the structure of the bulk Rh₂O₃ corundum oxide using surface X-ray diffraction. Being armed with this structural information, we have explored the CO oxidation reaction over Rh(1 1 1), Rh(1 0 0) and Pt₂₅Rh₇₅(1 0 0) at realistic pressures using in situ surface X-ray diffraction and online mass spectrometry. In all three cases we find that an increase of the CO₂ production coincides with the formation of the thin RhO₂ surface oxide film. In the case of Pt₂₅Rh₇₅(1 0 0), our measurements demonstrate that the formation of bulk Rh₂O₃ corundum oxide poisons the reaction, and argue that this is also valid for all other Rh surfaces. Our study implies that the CO oxidation reaction over Rh surfaces at realistic conditions is insensitive to the exact Rh substrate orientation, but is rather governed by the formation of a specific surface oxide phase.     

The High Resolution NMR Structure of Parvulustat (Z‐2685) from Streptomyces parvulus FH‐1641: Comparison with Tendamistat from Streptomyces tendae 4158

The protein parvulustat (Z‐2685) from Streptomyces parvulus comprises 78 amino acids and functions as a highly efficient α‐amylase inhibitor. Parvulustat shares 29.6 % overall amino acid sequence identity to the well‐known α‐amylase inhibitor tendamistat. Among the conserved residues are the two disulfide bridges (C9–C25, C43–C70) and the active‐site motif (W16, R17, Y18). Here, we report the high‐resolution NMR structure of parvulustat based on NOEs, J couplings, chemical shifts and hydrogen‐exchange data. In addition, we studied the dynamical properties of parvulustat by heteronuclear relaxation measurements. We compare the structure of parvulustat with the structure of tendamistat in terms of secondary structure elements, charges and hydrophobicity. The overall structural composition is very similar, but there are distinct differences including the active‐site region. These structural and dynamical differences indicate that for parvulustat an induced‐fit mechanism for binding to α‐amylase might take place, since the structure of tendamistat does not change upon binding to α‐amylase.     

Einfluß einer Mitteldehnung auf das Ermüdungsverhalten der Aluminiumlegierung AlMg5Mn

The effect of a superimposed mean strain on the fatigue behavior of the aluminum alloy AlMg5Mn The cyclic stress-strain response of the aluminum alloy AlMg5Mn in three different strength conditions is studied with emphasis on the influence of a superimposed mean strain and mean stress, respectively. The cyclic deformation behavior is characterized by a pronounced cyclic saturation independent of the prior heat treatment. Decreasing strength of the material is connected with a increasing extent of mean stress relaxation and cyclic creep, respectively. However, these transient effects are mainly restricted to the initial stage of cyclic life. In order to validate the lifetime data observed, a comparison with data from the literature is performed. For this purpose, it is necessary to apply a damage parameter which takes the damaging effect of a mean stress into account, since the cyclic lifetime values reported have mostly been obtained in tests without mean stress or mean strain. It is found that the damage parameter PSWT after Smith, Watson and Topper is suitable for the two conditions with higher strength. In the case of the soft condition, the damage caused by plastic mean strain is underestimated. As a consequence the cyclic lifes observed lie at the lower boundary of the scatter band of the literature data.