bluuebunny/crossref_metadata_2025_split huggingface dataset:
Strukturelle, elektronische und magnetische Eigenschaften komplexer intermetallischer Verbindungen Progress Report
Authors: Hafner J. 
Published: July 2012

AbstractIn recent years, the theory of alloys has progressed on three different levels. On the first level, favoured by physicists, the properties of alloys are calculated by solving the Schrödinger equation in the local‐spindensity (LSD) approximation. Given the high accuracy that is required, such calculations can be performed only for systems with a maximum of hundred nonequivalent atomic sites, even on the most powerful computers. On the second level, chemists describe bonding in terms of the σ, π and δ transfer integrals resulting from the angular‐dependent valence orbitals. Chemical intuition allows to introduce simplifications, and at the reduced accuracy of a Tight‐Binding‐Hückel equation, systems with up to a few thousand atoms may be modelled quite successfully. The third level corresponds to the reasoning traditional in metallurgy: atoms are considered as soft spheres interacting through pair – or embedded‐atom potentials. The simplicity of the interatomic force law allows to simulate the properties of ensembles with up to a hundred thousand atoms. – Progress on all three levels will be illustrated at the example of crystalline and liquid Zintl phases, of crystalline and amorphous magnetic alloys, and of quasicrystalline alloys.
Crystal Structure and Thermodynamic Analysis of the New Semiconducting Chevrel Phase Re6S8Cl2
Authors: Fischer C. , Fiechter S. , Tributsch H. , Reck G. , Schultz B. 
Published: July 2012

AbstractRe6S8Cl2 single crystals have been synthesized by chemical vapour transport with chlorine as transporting agent. Structure analysis revealed that the material is isomorphous with Re6S8Br2 and Re6Se8Br2 but not with the lamellar Re6Se8Cl2. The thermal stability of this semiconducting rhenium cluster compound was simulated as a function of vapour phase composition by thermochemical calculations in the ternary system Re–S–Cl at temperatures 1000, 1200 and 1400 K. Predominance‐area phase diagrams indicate that Re6S8Cl2 can coexist with Re and ReS2 depending on the vapour pressure ratios of S2/S2Cl2 and Cl2/Re3Cl9.
Chemical Activities in the Solid Solution of Hf in Ni3Al
Authors: Albers M. , Sai Baba M. , Kath D. , Miller M. , Hilpert K. 
Published: July 2012

AbstractThe vaporization of the alloy samples of the compositions (Ni3Al)1‐xHfx, x = 0, 0.010, 0.030, 0.052, 0.070, 0.089, and 0.100, as well as Ni0.75Al0.25‐xHfx, x = 0.020, 0.040, 0.060, 0.080, and 0.100, was investigated at temperatures between 1361 and 1680 K in order to obtain information on the chemical bond in the solid solution of the γ' phase of the type Ni3Al. The partial pressures of Ni and Al were determined by calibration with pure nickel. Chemical activities and excess chemical potentials were evaluated for the solid alloys below the temperature of incipient melting and also in part for the melt. The excess chemical potentials obtained for the γ' phase indicate the substitution of Hf for Al in the γ' or Ni3Al phase.
Elektronische und magnetische Eigenschaften von Alkalidithioferraten(III)
Authors: Bauer M. , Meyer M. , Nagorny K. 
Published: July 2012

AbstractThe isomeric shift of KFeS2, RbFeS2 and Kx Rb1‐x FeS2 is δ = 0.16 mm/s. This value can only be explained with partial occupation of the 4s‐niveau of iron which results from covalent parts of the Fe–S‐bonding as well as the transfer of electron density from sulfur into the 3d‐orbital of iron. – These effects must lead to spin pairing which is besides the additional occupation of the 4s‐niveau and the zero point spin fluctuations responsible for the low hyperfine fields. – The unusually high ordering temperatures could be identified as transition temperatures to antiferromagnetic long distance order. The one‐dimensional interactions remain up to the decomposition temperatures.
35Cl NQR and Crystal Structure Studies of Dimeric Trichloroalcoxystannane Alcoholates
Authors: Sinsel Bernd , Dou Shi‐Qi , Weiss Alarich 
Published: July 2012

AbstractThe 35Cl NQR spectra of the dimeric complexes bis‐[μ‐methoxytrichloromethanolatostannane] (a) and bis‐[μ‐ethoxy‐trichloroethanolatostannane] (b) have been recorded as a function of temperature in the range 77 ≤ T/K ≤ 389 for (a) and 77 ≤ T/K ≤ 363 for (b). The crystal structure of the methanolato stannane (a) [1] was refined by 4‐circle X‐ray diffractometry. [H3COSnCl3·CH3OH]2 (a): C–P21/c, Z = 2; a = 726.2 (3) pm, b = 1247.2 (4) pm, c = 1143.2 (4) pm, β = 126.76 (1)°. (a) undergoes a phase transition in the range 146 K ± 161 K. Three 35Cl NQR lines are observed in the high temperature phase (I). The low temperature phase (II) shows four 35Cl NQR lines. In both phases of (a) the temperature coefficient of the lowest frequency 35Cl NQR line is positive. – No phase transition in (b), [H5C2‐OSnCl3·C2H5OH]2, isomorphous [2] to phase (I) of (a), was observed in the temperature region covered by the 35Cl NQR experiment. A 35Cl NQR triplet was observed and the three frequencies showed normal “Bayer‐type” temperature dependence. – The correlation between Sn–Ci bond lengths and 35Cl NQR frequencies is discussed for both compounds as is the influence of intramolecular R–O–HCl–Sn hydrogen bonding. (R = CH3, C2H5).
Proton Conductivity: Compounds and their Structural and Chemical Peculiarities
Authors: Kreuer K. D. , Dippel Th. , Hainovsky N. G. , Maier J. 
Published: July 2012

AbstractThe problem of proton conductivity in condensed matter is summarized from a phenomenological point of view. Different families of compounds with proton conductivity are distinguished with particular emphazise on their conduction mechanism. Finally some structural peculiarities typically occuring with proton conductivity are extracted from the comparison of data from good and poor proton conductors.
Anomalous H Mobility in NbHxDy and Other Metal‐Hydrogen Systems: Protonic Coherent‐Dissipative Structures
Authors: Chatzidimitriou‐Dreismann C. A. 
Published: July 2012

AbstractThe possibility of protonic quantum effects in metal‐hydrogen systems is discussed, in connection with current theoretical (Complex Scaling Method (CSM), Einstein‐Podolsky‐Rosen (EPR) correlations, coherent‐dissipative structures) and experimental work (on detection of coherent‐dissipative structures of protons in water at room temperature). The following two effects are considered:

The measurement of the diffusion coefficient DH of H in NbHxDy, with x+y = const. (e.g. = 0.60) with NMR, shows a striking decrease of DH (up to one order of magnitude) with decreasing H‐concentration.
The comparison of mobilities of H and μ+ in different metal hydrides reveals the surprising feature that muons (as measured by	μSR) apparently diffuse slower than hydrogen (as measured in the absence of muons by neutron scattering) in a large temperature regime.
These effects are interpreted in a natural way within the framework of the CSM‐theory, where broken EPR correlations between protons in the presence of other particles (muons or deuterons) are taken into consideration. As a result, the characteristic length of the protonic coherent‐dissipative structures is shown to be about (1–3)X(lattice constant). – A new prediction of the CSM‐theory concerning neutron scattering on metalhydrogen systems is stated explicitly.
Theoretical Investigation on the Luminescence Transition Probabilities in the Phosphor ZnO:Cu
Authors: Nedelmann L. P. , Mishra K. C. , Sticht J. , Schmidt P. C. 
Published: July 2012

AbstractOptical properties of ZnO:Cu have been studied using the ASW (augmented spherical wave) band structure method and a supercell approximation to simulate copper impurities. The imaginary part of the dielectric function ϵ2(ω) is calculated in two different ways. In the first calculation, it is assumed that ϵ2(ω) is proportional to the joint density j(E) whereas in a second calculation the dependence of the dipole transitions on the wave vector is taken into account. The comparison of both calculations gives relative oscillator strengths for the different dipole transitions. Furthermore the influence of the choice of atomic sphere radii on the calculated j(E) is studied.
Modelling the Oscillating Electrochemical Reduction of Peroxodisulfate
Authors: Wolf W. , Ye J. , Purgand M. , Eiswirth M. , Doblhofer K. 
Published: July 2012

AbstractWe present a dynamic model for the oscillatory reduction of anions such as S2O82− on different electrodes. The model is solely based on well known electrochemical formulae so that the mechanism can be well understood. The central mechanistic feature is a region of negative differential resistance in the cathodic current/overvoltage curve. It is caused by the repulsive electrostatic interaction between the anions and the negative electrode surface, which counteracts the effect of increasing overvoltage. The model is investigated with numerical techniques from the theory of nonlinear dynamics. The calculations turn out to be in good agreement with experiment.
Diffusion Coefficients for Binary Mixtures of Neon with Argon, Krypton and Xenon from 220 to 400 K
Authors: Dunlop Peter J. , Bignell C. M. 
Published: July 2012

AbstractDiffusion coefficients are reported for binary mixtures of neon with argon, krypton and xenon from 220 to 400 K. Potential functions are derived from these diffusion coefficients and the second virial coefficients in the literature.
Thermal Variation of the EPR Linewidth of new Phosphoniumyl Free Radicals for NMR Magnetometers
Authors: Ferroud‐Plattet M. P. , Belorizky E. , Berchadsky Y. , Tordo P. 
Published: July 2012

AbstractThe temperature dependence of the EPR linewidth of two phosphoniumyl radicals is investigated between 193K and 353K. The observed behaviour is interpreted through a simple model which assumes that the main contribution to the EPR linewidth arises from the anisotropic component of the large hyperfine coupling of the unpaired electron with the phosphorus nucleus. However the non resolved hyperfine coupling with the protons of the ortho methyl substituents is shown to contribute significantly to the broadening of the EPR linewidths in the high temperature range. The EPR features of the two radicals are discussed to evaluate their usefulness in low field NMR magnetometers.
Solvent Density Dependence of the Dissociation Rates of 2‐Methyl‐2‐Nitrosopropane Dimer in Simple and Molecular Fluids
Authors: Kimura Y. , Yoshimura Y. 
Published: July 2012

AbstractThe dissociation rate constants of 2‐methyl‐2‐nitrosopropane dimer are studied in argon, xenon, carbon dioxide (CO2) chlorotrifluoromethane (CClF3), and trifluoromethane (CHF3) from the gaseous to liquid state at 25.0 and 35.0°. In all solvent fluids, the dissociation rate constant is a decreasing function of solvent density. In argon, xenon, and CClF3, the rate constant at 35° gradually decreases by about 50% with increasing solvent density from ρr ≈︁ 0.0 up to 2.5, where ρr is a reduced density by the critical density of the solvent. In CO2 and CHF3, however, the rate constant shows a large and nonmonotonic dependence on solvent density; the solvent density dependence is large in the low‐ (ρr < 0.5) and high‐(ρr > 2.0) density regions, and is small in the medium‐density region (0.5 < ρr < 1.7). The density dependence of the rate constant in argon and xenon is well reproduced by the Lennard‐Jones fluid model on the basis of the transition state theory. The change in the charge distribution of the reactant molecule is a key to explain the large and nonmonotonical density dependence of the rate constant in CO2 and CHF3.
Adsorption of CO, H2, and O2 on Co3O4
Authors: Gamboa Mutuberría I. , Guil J. M. , Paniego Ruiz 
Published: July 2012

AbstractSamples of cobalt oxide, Co3O4, have been prepared by calcination in air of cobalt nitrate, Co(NO3)2 · 6H2O. Samples with different surface areas have been obtained by sintering at several temperatures. The adsorption of carbon monoxide, hydrogen, and oxygen on these samples have been measured in a volumetric apparatus in a temperature range from 77 to 373 K. Two kinds of adsorption experiments have been carried out: normal isotherms and kinetic measurements in which the evolution of pressure is monitored as a function of time. In all cases, total and reversible adsorption are measured and irreversible adsorption is calculated. Kinetic results have been analyzed with the aid of the Elovich equation. Isosteric heats of adsorption have been calculated and calorimetric heats have been measured for the system COCO3O4 with a Tian‐Calvet microcalorimeter. From these results it is possible to draw conclusions concerning the nature of the interaction of Co3O4 with the three adsorbates.
An Experimental and Theoretical Investigation on the Solubility of Carbon Dioxide in Aqueous Solutions of Strong Electrolytes
Authors: Rumpf B. , Maurer G. 
Published: July 2012

AbstractAs part of an ongoing project dealing with the measurement and correlation of phase equilibria in aqueous solutions containing a weak base like ammonia and acid gases like carbon dioxide, sulfur dioxide and hydrogen cyanide, the solubility of carbon dioxide was measured in aqueous solutions containing the single salts sodium sulfate and ammonium sulfate as well as in a solution containing both salts. The temperature ranged from 313.15 K to 433.15 K and pressures up to 10 MPa. Pitzer's semiempirical model is used to correlate the new data. From the results for the solubility of carbon dioxide in the single salt aqueous solutions, interaction parameters were determined. With these parameters the solubility of carbon dioxide in an aqueous mixture containing both salts is predicted quantitatively.
Efficiency of the Generation of Protons and Hydroxyl Ions in Bipolar Membranes by Electric Field Enhanced Water Dissociation
Authors: Dang Ngoc‐Ty , Woermann D. 
Published: July 2012

AbstractThe efficiency of the production of protons and hydroxyl ions generated by electric field enhanced water dissociation within bipolar membranes is studied as function of the electrolyte concentration. Two types of bipolar membranes are used for the experiments: (a) A bipolar membrane formed by an anion and a cation exchange membrane which are held together by adhesion. The volume of the transition region between the two ion exchange membranes is varied systematically by inserting stacks of Nucleopore membranes. (b) A bipolar membrane formed by an anion and a cation exchange membrane are bound together permanently. The results are discussed in terms of the model of the membrane with narrow pores. The space charge model proposed in the literature to describe the electrochemical properties of bipolar membranes is modified to interprete the properties of the bipolar membranes of type (a) with a stack of Nucleopore membranes in the enlarged transition zone between the anion and the cation exchange membrane.
CO Hydrogenation on Supported Cobalt Catalysts Studied by in situ FTIR‐Spectroscopy
Authors: Fredriksen G. R. , Blekkan E. A. , Schanke D. , Holmen A. 
Published: July 2012

AbstractCO hydrogenation on silica and alumina supported Co catalysts has been studied using in situ IR spectroscopy at 473–523 K, 6 bar and H2/CO=2. Bands corresponding to linearly adsorbed CO appeared at 2072 cm−1 on 4.7% Co/SiO2 and 2062 cm−1 on 4.6% Co/γ‐Al2O3, while a pair of bands at 1996 and 1952 cm−1 is observed on the alumina supported Co catalyst. Infrared bands in the 3100–2700 cm−1 and 1700–1200 cm−1 regions are attributed to adsorbed hydrocarbons, surface formate and carbonate species. The variation of the band intensities with time during CO hydrogenation and subsequent treatment in He or H2, indicates that these structures represent reaction products, apparently adsorbed on the support.
The Effect of 2,6‐Dimethylpyridine Poisoning on the Activity in n‐Hexane Cracking of Dealuminated HY Zeolites
Authors: Jolly S. , Saussey J. , Lavalley J. C. , Zanier N. , Benazzi E. , Joly J. F. 
Published: July 2012

AbstractThe use of an IR cell as a flow reactor shows that the activity of dealuminated HY zeolites in n‐hexane cracking at 673 K can be related to hydroxyl groups giving rise to a band at 3600 cm−1. Their presence is connected to extraframework Al species and they are strongly acidic. Specific poisoning experiments with 2,6‐dimethylpyridine evidence their heterogeneity, only a part of them being responsible for the observed activity.
In‐situ Raman Studies of Ethylene Oxidation at Ag(111) and Ag(110) under Catalytic Reaction Conditions
Authors: Bao X. , Pettinger B. , Ertl G. , Schlögl R. 
Published: July 2012

AbstractIn this report we present, to our knowledge, the first Raman investigations at single crystalline Ag(111), Ag(110) and microfacetted Ag(110) samples, which were exposed to N2 or N2 + reactive gases (oxygen and ethylene). The pressure and temperature ranges are close to those used for industrial oxidation of ethylene using Ag‐catalysts. Depending on the orientation of the Ag‐surface and on the history its preparation and temperature cycling (300–900 K), three Raman lines for three Ag—O species were found, assigned to Ag—Oads., —Ag—O—Ag— with oxygen located in the sub‐surface position and oxygen dissolved in the bulk of silver. The disappearence of the Raman line for sub‐surface oxygen in the course of ethylene epoxidation indicates its participation in this reaction.
In‐situ Positron Emission of CO Oxidation
Authors: Vonkeman K. A. , Jonkers G. , van Der Wal S. W. A. , van Santen R. A. 
Published: July 2012

AbstractUsing a Neuro ECAT positron tomograph the Positron Emission computed Tomography (PET) has been utilized to image the catalytic oxidation of CO by using CO and CO2, labelled with short lived positron emitting nuclides. Studies were performed over highly dispersed ceria/γ‐alumina supported platinum and rhodium catalysts. With a mathematical model of the reaction kinetics, based on the elementary steps of the catalytic reaction and partially on literature surface science data, the effect of CeO2promotion and the presence of NO were quantified in terms of the number of adsorption sites and adsorption equilibrium constants. Oxygen atoms of CO2remain much longer in the catalyst bed than the carbon atoms, which is due to carbonate formation at the ceria surface and exchange of the oxygen atoms of these carbonate groups with the ceria lattice oxygen atoms. The heat of desorption of CO from the noble metal surface at low temperatures was found to be increased due to the presence of NO molecules at the surface. At higher temperatures NO dissociates, the adsorbed N and O atoms have a repulsive interaction with adsorbed CO molecules.
In Situ AC Electrical Conductivity Measurement on Bi3FeMo2O12
Authors: Cäldararu Monica , Sprinceana Dan , Ionescu Niculae I. 
Published: July 2012

AbstractThe dynamic evolution of the defect structure of the Bi3FeMo2O12 surface determined by processes frequently encountered in heterogeneous catalysis (e.g. heating‐cooling cycles, adsorption and/or reaction of reactive gases with solid surfaces) can be followed either by direct in situ measurement of the AC electrical conductance, or by comparing the electrical conductance data of successive experiments on the same sample, in standard reference conditions, after various in situ treatments.
In situ ESR‐Untersuchungen an elektrochemischen Systemen
Authors: Dunsch L. , Petr A. 
Published: July 2012

AbstractThe combination of ESR‐spectroscopic measurements with electrochemical techniques is described using a new ESR‐electrochemical cell for studies of solid working electrodes and a computer‐driven system for both the electrochemical and the spectroscopic technique. The variation of the cell construction for different applications as well as the use of signal accumulation after potentiostatic pulses is shown. In the case of a triazine the existence of two radical products in an electrode reaction is proved using the rapid scan ESR‐technique.
The Adsorption of Unsaturated Organic Species at Single Crystal Electrodes Studied by Differential Electrochemical Mass Spectrometry
Authors: Baltruschat H. , Schmiemann U. 
Published: July 2012

AbstractUsing a thin layer cell for differential electrochemical mass spectrometry, we studied the influence of the crystallographic surface orientation of Pt single crystals on the adsorption of benzene, ethene and perchloroethylene. Whereas on Pt(110), adsorbed benzene is completely desorbed at negative potentials under hydrogenation to cyclohexane, it is desorbed as such from the (111) face. — Several adsorbate states are found when ethene is adsorbed on these surfaces. Only part of the adsorbate can be desorbed under hydrogenation to ethane and also dimerization to butane; the extent of this hydrogenative desorption being much higher in the case of the (110) surface. The remaining part of the adsorbate can be oxidized to CO2 at potentials where oxygen is coadsorbed. In addition, at the (110) face and, at higher adsorption potentials also at the (111) face, some CO‐like adsorbate is formed during adsorption. — In the case of perchloroethylene, the adsorption is reductive, i.e. the C—Cl‐bonds dissociate upon adsorption. Cathodic desorption also yields methane besides ethane pointing also to a C—C bond dissociation.
Processes at Interfaces between Solid Electronic, Ionic and Mixed Conductors — Characterization by Voltage and Frequency Dependent Electrical Measurements
Authors: Wiemhöfer H.‐D. 
Published: July 2012

AbstractExamples are discussed for the electrical characterization of interfaces with solid electronic, ionic and mixed conductors by steady‐state current voltage relations and impedance spectroscopy. Polarization measurements are presented with electron and ion conducting point contacts on mixed conducting solids. Examples for the use of impedance spectroscopy concern the effect of fast grain boundary transport on diffusion impedances in mixed conductors and the impedance of electrodes on solid electrolytes. The experimental realization of in‐situ investigations with XPS and UPS are discussed for oxygen electrodes with yttria‐stabilized zirconia as solid electrolyte.
Impedance Analysis of the Quartz Micro‐Balance Signal
Authors: Fruböse Christian , Doblhofer Karl , Soares David M. 
Published: July 2012

AbstractDuring measurements of mass‐changes with the electrochemical quartz‐microbalance (E‐QMB) changes of the visco‐elastic properties of the contacting medium (liquids and/or films) can occur. If such changes are not taken into account in the evaluation of the observed frequency‐changes, erroneous results will normally be obtained. The problem is analyzed on the basis of the system's impedance. Methods for correcting results obtained with impedance‐analyzers and with feedback‐driver circuits are presented.
Probing Electrochemical Adsorbate Structure and Reactions with In‐Situ Atomic‐Resolution Scanning Microscopy: Some Progress and Prospects
Authors: Gao Xiaoping , Weaver Michael J. 
Published: July 2012

AbstractSome prospects for applying scanning tunneling microscopy (STM) as an in‐situ atomic‐resolution probe of adlayer structure at ordered metal‐solution interfaces are considered with respect to both equilibrium and reactive adsorbate systems. Illustrative results of the former type are presented for the potential‐dependent adsorption of iodide at low‐index gold electrodes. The virtues of acquiring “composite‐domain” STM images, where the electrode potential is altered during data acquisition so to form or remove the adsorbed adlayer, are noted. By generating temporally and spatially adjacent domains featuring substrate and adlayer images in this fashion, the registry between the former and latter atomic arrangements can be deduced with high precision. The suitability of in‐situ STM for examining real‐space dynamics of surface physical and chemical processes is illustrated for potential‐induced reconstruction of Au (100) and for the electrooxidative polymerization of iodide and sulfide. Some limitations as well as strengths of in‐situ STM for these purposes are briefly outlined with regard to its anticipated role in the development of in‐situ electrochemical surface science.