The crystal growth and properties of novel magnetic double molybdate RbFe5_{5}(MoO4_{4})7_{7} with mixed Fe3+^{3+}/Fe2+^{2+}states and 1D negative thermal expansion

Single crystals of new compound RbFe$_5$(MoO$_4$)$_7$ were successfully grown by the flux method, and their crystal structure was determined using the X-ray single-crystal diffraction technique. The XRD analysis showed that the compound crystallizes in the monoclinic space group P21/m, with unit cell parameters a = 6.8987(4), b = 21.2912(12) and c = 8.6833(5) Å, β = 102.1896(18)°, V = 1246.66(12) Å$^3$, Z (molecule number in the unit cell) = 2, R-factor (reliability factor) = 0.0166, and T = 293(2) K. Raman spectra were collected on the single crystal to show the local symmetry of MoO$_4$ tetrahedra, after the confirmation of crystal composition using energy dispersive X-ray spectroscopy (EDS). The polycrystalline samples were synthesized by a solid-state reaction in the Ar atmosphere; the particle size and thermal stability were investigated by scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) analyses. The compound decomposes above 1073 K in an Ar atmosphere with the formation of Fe(III) molybdate. The thermal expansion coefficient along the c direction has the value α = −1.3 ppm K$^{−1}$ over the temperature range of 298–473 K. Magnetic measurements revealed two maxima in the magnetization below 20 K, and paramagnetic behavior above 50 K with the calculated paramagnetic moment of 12.7 μB per formula unit is in good agreement with the presence of $_3$Fe$^{3+}$ and $_2$Fe$^{3+}$ in the high-spin (HS) state. The electronic structure of RbFe5(MoO4)7 is comparatively evaluated using X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations

Neutron reflectometry studies on the lithiation of amorphous silicon electrodes in lithium ion batteries

Neutron reflectometry is used to study in situ the intercalation of lithium into amorphous silicon electrodes. The experiments are done using a closed three electrode electrochemical cell setup. As a working electrode, an about 40 nm thick amorphous silicon layer is used that is deposited on a 1 cm thick quartz substrate coated with palladium as a current collector. The counter electrode and the reference electrode are made of lithium metal. Propylene carbonate with 1 M LiClO4 is used as an electrolyte. The utility of the cell is demonstrated during neutron reflectometry measurements where Li is intercalated at a constant current of 100 [small mu ]A 7.8 [small mu ]A cm 2 for different time steps. The results show a that the change in Li content in amorphous silicon and the corresponding volume expansion can be monitored, b that the formation of the solid electrolyte interphase becomes visible and c that an irreversible capacity loss is presen

FT Raman und FTIR Untersuchungen zur Qualitaetskontrolle und Alterung von Papier

Paper is a complex material composed of plant fibres, fillers, adhesives, coatings and a variety of other materials, each of them added to the pulp to give the resulting paper specific properties, e.g. colour, opacity, mechanical stability, reduced porosity etc. The long-term stability of paper and board materials arises from their composition and structure. In order to assess the condition and ageing characteristics of paper it is necessary to understand the phenomena leading to its degradation and to be able to investigate the resulting chemical and mechanical alterations. The degradation of paper has been identified by a number of chemical reactions, especially hydrolysis and oxidation, further cross-linking of the cellulose. The presence of certain additives such as acid contaminants being present due to internal or external factors within the paper, transition metal ions, lignin etc. play an important role in generating the composition of paper. Among the external influences on the ageing characteristics, the effects of atmospheric pollutants and the stability of relative humidity in the environment are very important. This paper describes two applications of vibrational spectroscopy with regard to quality control and ageing of paper: continuous scan FTIR (Fourier Transform infrared) and FT Laser Raman spectroscopy. These techniques have been tested on samples of industrial papers, as well as in laboratory aged samples. The results indicate the feasibility of FTIR / Raman spectroscopy for the determination of the amount of lignin in various papers and the light induced oxidation of lignin. Furthermore the carbonates content is measured which is very important to the acidity content of paper. (orig.)Available from TIB Hannover: ZA 5141(6468) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Herstellung von duennen sensitiven Membranen fuer Gas- und elektrochemische Sensoren mittels HF-Magnetron-Co-Sputtern

For the development of novel miniaturized chemical sensors and sensor systems the definite production of thin sensitive and/or functional layers is of fundamental importance. For this aim built-up, structure, and composition of the layers have to be adjusted to the respective problem and optimized for the planned application. Furthermore, reproducibility of the fabricated layers as well as the suitability of the applied process for a lateron mass production has to be guaranteed. For this purpose, at the Institute of Instrumental Analysis of the Forschungszentrum Karlsruhe several sputtering set-ups have been constructed on the basis of RF magnetron cathodes using standard UHV technique. This ensures on one hand a high purity of the produced layers. On the other hand, as an indispensable prerequisite for the development phase, it is possible to vary and exchange the used components easily. The most important step of the present work was the development of special co-sputter targets enabling the defined and reproducible fabrication of multicomponent systems using only a single sputtering cathode. Purity, stoichiometry, and reproducibility of the layers was checked and proved by means of ample surface analytical investigations. (orig.)Available from TIB Hannover: ZA 5141(5852) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman