bluuebunny/crossref_metadata_2025 huggingface dataset:
New Copper Phosphates as Ionic or Mixed Conductors
Authors: Warner T. E. , Milius W. , Maier J.
Published: July 2012

As part of a search for solid‐state copper ion conductors, new copper phosphate compounds of the Nasicon or alluaudite type structure were synthesized. Compounds with the former structure are reported here in more depth. CuTiZrP3O12 and the previously prepared compound CuTi2P3O12 were found to be copper ion conductors with a relatively low electronic contribution, and comparable both in structure and in conductivity behaviour to both CuZr2P3O12 and the NaZr2P3O12 end‐member of the classical Nasicon composition range. In contrast to the Cu(I) halide conductors these phases are stable under ambient conditions. Partial substitution of Zr by Sc, or Ti by Cr (rather than Si for P) results in a new Cu‐rich compound Cu2ZrScP3O12, together with the previously prepared compound Cu2TiCrP3O12, both showing expectedly very high Cu+ conductivity comparable to Nasicon compounds with a similar charge carrier concentration. A new related phase CuTiCrP3O12 was also synthesized. Magnetic measurements, Wagner‐Hebb polarization and e.m.f. measurements performed to elucidate partial conductivity contributions and valence states are discussed. The e.m.f. results obtained with Cu‐activity cells reveal a predominant ionic conductance together with a minor but not negligible electronic contribution resulting in a fast copper diffusion. Cu–Fe and Cu–Mg phosphates were also prepared for the first time as first examples of quaternary compounds in the Cu–Fe–P–O and Cu–Mg–P–O system respectively. These materials, Cu1,3Fe3P3O12 and Cu2Mg3P3O12 were found to be of the alluaudite structure type, with predominant electronic conductivity at high temperature.
Electronic Structure of B2‐NiTi and ‐PdTi
Authors: Bihlmayer G. , Eibler R. , Neckel A.
Published: July 2012

The electronic structure of B2‐phase NiTi and PdTi is determined by means of the self‐consistent Linearized Augmented Plane Wave (LAPW) method. The bandstructures, local densities of states and electron densities for the two compounds are compared and the differences analyzed. The calculated broadened DOS show close resemblance with measured photoelectron spectra. Accurate calculations of the Fermi surface and some Fermi surface‐related properties are also presented. We investigate the topology of the Fermi surface and calculate the generalized susceptibility of non‐interacting electrons and, approximately, the electron‐phonon contribution to the dynamical matrix of phonons, in order to estimate the influence of nesting regions on the electron‐phonon coupling, thus establishing a relation between the electronic structure and the martensitic transformations of these compounds. The calculations suggest that the appearance of “bottle‐necks” in the Fermi surface of PdTi may be responsible for the different transformational behaviour of these two alloys.
Defect Model Applied to the Diffusion in the Intermetallic Phases ε‐(Ag, Sn) and ε‐(Cu, Sn)
Authors: Schwitzgebel G. , Rupp R.
Published: July 2012

A substitutional defect model of binary hexagonal closed packed structures is developed based on interactions of nearest neighbours and on the configurational entropy of randomly distributed deviations from stoichiometry. The dependence of the thermodynamic quantities on composition can be expressed within the homogeneity range by an order parameter. – With the thermodynamic data of ε‐(Ag, Sn) and ε‐(Cu, Sn) the order parameters of Ag3Sn and Cu3Sn were determined (523 K–623 K) and used for calculating Sn‐activity curves of the the phases. By the help of these curves chronoamperometric diffusion experiments could be evaluated. The contributions of the bulk material and the grain boundaries to diffusion are given by volume and grain boundary diffusion coefficients.
7Li‐NMR Study of Diffusion‐Induced Spin‐Lattice Relaxation in Glassy and Crystalline LiAlSi2O6
Authors: Franke W. , Heitjans P.
Published: July 2012

In order to study the effect of structural disorder on the diffusion of mobile ions, both the glass Li2O · Al2O3 · 4SiO2 and its crystalline counterpart (β‐spodumene) were investigated by 7Li‐NMR. The spinlattice relaxation (SLR) time T1 of 7Li was measured as a function of temperature T from 150 K to about 960K in the glass (glass transition temperature) and 1300 K in the polycrystalline sample. The frequency ν was varied in the range 10 MHz to 100 MHz. Both in the glass and the crystal a diffusion‐induced peak in T1−1(T) was observed. Comparison of the positions of the maxima and the slopes of the low‐T sides of log T1−1 vs 1/T curves shows that the Li+ jump rate in the glass is higher and the activation energy is lower than in the crystal. In both cases the ν and T dependences of the diffusional SLR rate strongly deviate from the BPP model. In particular, the ν dependence of T1−1 on the low‐T sides is sublinear or, at most, linear. The activation energies obtained from the temperature regime above the maximum and those below at various frequencies are briefly compared with corresponding values from a.c. impedance measurements on the same samples.
Magnetic and EPR Spectroscopic Investigations on a Ferromagnetic Coupled Trinuclear Cu(II) Complex
Authors: Fleischhauer P. , Gehring S. , Haase W.
Published: July 2012

Magnetization measurements and X‐band EPR investigations on the trimeric exchange coupled Copper(II)‐complex [(Cu3(C6H5CO2)4{(C)2NC2H4O}2(CH3OH)2] are reported. The field dependence of the magnetization at 3.7 K is consistent with a quartet ground state and proofs that ferromagnetic exchange coupling is operative between adjacent Cu(II) – centres in the trimeric molecule. – A strong temperature dependent variation of the g value from geff ≈︁ 4.3 at liquid helium temperature to geff ≈︁ 2.6 at room temperature was observed in the EPR experiment. Different explanations for the g shift are discussed.
Ein Verfahren zur Berechnung der temperaturabhängigen Suszeptibilität itineranter Systeme aus Grundzustandsgrößen
Authors: Kirchner B. , Weber W. , Voitländer J.
Published: July 2012

The temperature dependence of magnetic properties of itinerant electron systems is predominated by the excitation of spin fluctuations. To describe the energy of the spinfluctuation field, we use a functional, which treats the fluctuation modes only in the static limit and which includes the energy of the coupling between different modes in a local, i.e. wavevector‐independent way. Along the lines of the Murata‐Doniach approach we derive formulas for the free energy and the susceptibility of the system, using a variational principle. Except for the approximations mentioned above our energy functional is quite general, going beyond the Ginzburg‐Landau expansion. It is possible to deal with arbitrary fluctuation amplitudes. Furthermore the energy functional can be completely derived from first principle calculations for the ground state of the system. Thermodynamic properties may thus be traced back to details of the bandstructure. We apply our method to the calculation of the temperature dependent susceptibility of Pd metal and PdAg with very small Ag concentrations.
Lateral Interaction between Adsorbates at Ionic Surfaces: Theoretical Investigation of the CO Vibrational Frequency Shift at MgO(001)
Authors: Neyman Konstantin M. , Rösch Notker
Published: July 2012

The adsorption of CO molecules at the MgO(001) surface is investigated by the LCGTO‐LDF cluster method for the low‐coverage limit as well as for a monolayer coverage. A static adsorbate‐adsorbate contribution to the partial red shift of the C–O vibrational frequency with increasing surface coverage is calculated in agreement with experiment. This red shift is related to a small adsorbate‐to‐substrate σ charge transfer which modifies the electrostatic field on the surface and thus is a “solvent” effect. No transmission of the donated charge through the substrate is found. Both the low‐coverage and the monolayer models predict an approximate doubling of the C–O vibrational intensity as compared to free CO. This intensity enhancement derives to a large extent from a change of the π component of the CO dynamical dipole moment due to a Pauli repulsion between the adsorbate and the nearest‐neighbour surface anions.
Crystal Chemistry and Magnetic Behavior of Compounds RE3Mn4Sn4, RE = La, Ce, Pr, Nd, Sm and MM (Mischmetal)
Authors: Weitzer F. , Hiebl K. , Rogl P. , Noël H.
Published: July 2012

Novel ternary stannides RE3Mn4Sn4 have been synthesized by the arc melting technique, starting from the pure elements. All compounds with the early and large rare earth metals (RE = La, Ce, Pr, Nd, Sm) and mischmetal (MM) were found to be isotypic with the Gd3Cu4Ge4‐type (space group, Immm‐D2h25, No. 71; Z = 2). The crystal structure of the Gd3Cu4Ge4‐type stannides is a combination of structural slabs RESn2 of the AlB2‐type and slabs RE4Mn2Sn2, common to the ThCr2Si2type. The (Ce, Pr, Nd, Sm)3Mn4Sn4 compounds exhibit antiferromagnetism. For (Pr, Nd)3Mn4Sn4 an onset of a spinflip process is indicated at a magnetic field Hcrit > 2.5 Tesla. La3Mn4Sn4 as well as Ce3Mn4Sn4 show broad maxima of the susceptibility at T ∼ 300 K, possibly due to demagnetizing effects caused by valence instabilities. The manganese atoms carry localized effective moments of 3 μB and 5 μB, respectively.
Structure, Photoabsorption and Reversible Reactivity of Faujasite‐Supported Dispersions of CdO and SnO2
Authors: Wark M. , Schwenn H.‐J. , Schulz‐Ekloff G. , Jaeger N.
Published: July 2012

High dispersions of CdO and SnO2 in a faujasite matrix are obtained by consecutive ion exchange, alkaline precipitation and calcination. The particle sizes in the range 5 to 20 nm are inferred from electronic spectra, transmission electron microscopy and X‐ray diffraction. The correlation between the blue shift of the absorption edge and the particle size is described by the effective mass approximation. The reactivity of CdO dispersions for the formation of carbonate increases with decreasing particle size.
Influence of Incorporated Copper on the Formation, Solid State Structure and Electrochemical Properties of γ‐FeOOH
Authors: Schneider M. , Stratmann M.
Published: July 2012

It is well known, that the rate of the atmospheric corrosion of iron is slowed down considerably, if the metal is alloyed by small amounts of Cu. This effect is specifically pronounced during those times, when the metal surface is covered by thin electrolyte layers. As then the oxygen reduction is rate determining for the corrosion rate, the kinetics of the oxygen reduction is slowed down on Cu‐containing steels with respect to pure iron. On pure iron oxygen is reduced within the oxide scale at electron conducting oxide crystals. Such oxides contain high amounts of Fe2+ states and result from an electrochemical reduction of γ‐FeOOH. Therefore it is quite likely, that on Cu‐containing steel the solid state properties of the oxide scale are changed such, that the electronic conductivity decreases. – In this study model electrodes of Cu‐doped γ‐FeOOH are investigated. The morphology of the scale is analysed by SEM, the chemical state of Cu and Fe by XPS and the structure of the scale using FT‐IR spectroscopy. The results clearly show, that the morphology of the Cu‐doped oxide is changed significantly and XPS data suggest, that the reducibility of the doped oxide is much less than the one of undoped γ‐FeOOH.
The Electronic Structure of Crystalline Lithium Hydride – A Reduced Density Matrix Approach
Authors: Asthalter Tanja , Weyrich Wolf
Published: July 2012

Three directional Compton profiles J(q) of LiH were measured by means of 241Am γ‐ray scattering. The Fourier transforms (reciprocal form factors B(s)) were compared to the results from Löwdin‐orthogonalised wavefunctions and from a full solid‐state RHF calculation performed with the program CRYSTAL for various basis sets of different quality. The wavefunction that yielded best agreement with the experiment was then used to calculate two‐dimensional cuts through the one‐electron density matrix (ODM) in the main bonding directions both for the crystal and for clusters of variable size. From the off‐diagonal parts of the ODM it is possible to estimate the influence of small covalent contributions to the chemical bonding in LiH. The influence of different cluster orbitals is discussed as well as the question which cluster size already shows the main qualitative features of chemical bonding in the ODM of the crystal.
Investigation of Solid State Reactions and Solid‐Solid Phase Transformations with Time‐ and Temperature‐resolved X‐ray Powder Diffractometry
Authors: Epple M. , Cammenga H. K.
Published: July 2012

An X‐ray powder diffractometer has been equipped with a heatable sample holder which allows highly defined heating up to 250°C. A good temperature control permits isothermal as well as non‐isothermal runs. The applicability of time‐ and temperature‐resolved X‐ray powder diffractometry (TXRD) as a thermoanalytical method is demonstrated. Solid state reactions and solid‐solid phase transformations were investigated. As examples the phase transformation of phenanthrene and the dehydration of caffeine hydrate are presented. It is possible to extract the activation parameters for a solid state reaction from a single non‐isothermal run with a constant heating rate. The principles of the quantitative kinetic evaluation of time‐ and temperature‐resolved X‐ray powder diffraction data are outlined.
A High‐Temperature Mössbauer Study of Fayalite, Fe2SiO4: Cation Diffusion and Reactivity
Authors: Becker K. D. , Dreher S. , Wißmann S.
Published: July 2012

Results are reported of a Mössbauer study of fayalite at elevated temperatures. At the highest temperature used in our study (1130°C), spectra are found to be affected by cation diffusion. The oxygen partial pressure dependent broadening of the Mössbauer lines is discussed in the context of the lattice structure of Fe2SiO4, which provides two non‐equivalent sites for diffusion of the ferrous ions. The kinetics of the formation reaction of Fe2SiO4 from its quasi‐binary components FeO and SiO2 has been studied by means of time‐resolved Mössbauer experiments.
Electrochemistry in Aprotic Solvents Containing Anhydrous Perchloric Acid: Electroreduction of Imidazoles
Authors: Pekmez Kadir , Özyöruk Haluk , Yildiz Attila
Published: July 2012

The electroreduction behavior of imidazole and some of its derivatives on a Pt electrode in acetonitrile was investigated using cyclic voltammetry and controlled potential electrolysis. In a solution containing TBAP a broad reduction peak was observed whereas no reduction process was detected in LiClO4 solution. In the presence of a strong proton donor another reduction peak was observed at more positive potentials that was assigned to the catalytic reduction of protons through the protonated imidazoles. The effects of hydrogen bonding and the pKa values of the imidazoles on the reduction process are discussed.
Resonant Behaviour of the Si/Fluoride Interface: A method for testing the uniform accessibility of an electrode system
Authors: Chazalviel J.‐N. , Ozanam F.
Published: July 2012

The p‐Si/fluoride interface exhibits a resonant behavior in the anodic potential region. The resonance frequency is proportional to the interface current density. It is shown that the response of the interface to a potential step excitation provides a direct means for accessing the current distribution at the interface. When the current density is under mixed (mass transport + kinetic) control, this gives a simple test for the uniform accessibility of the electrode. This method is tested on a circulation cell, where the current distribution can be varied by changing the geometry. The obtained current distributions are qualitatively consistent with a numerical calculation of the current‐density map.
Fiber‐Optic Quasielastic Light Scattering in Concentrated Latex Dispersions: The Performance of Single‐Mode vs. Multimode Fibers
Authors: Wiese H. , Horn D.
Published: July 2012

Results of fiber‐optic quasielastic light scattering from two monodisperse latex dispersions (particle diam. 135 and 270 nm, concentration range 1 – 30 wt%) are compared for single‐ and multimode fibers, respectively. For the 135 nm latex dispersions it is shown both by theory and experiment that the two types of fibers give identical results which can be interpreted in terms of the diffusional motion of the latex particles. Evidence is given that in the case of the multimode fiber the speckle pattern, i.e. the inhomogeneous illumination of the particles in the scattering volume, and the dependence of the mode excitation on the position of the scatterer do not give rise to additional intensity fluctuations on the delay time scale of the measurements. Discrepancies observed between the results obtained with the two fibers for the 270 nm latex dispersions, are shown to be due to multiply scattered light affecting the multimode fiber data.
A Kinetic Investigation of the Reaction between F Atoms and Cl2O
Authors: Vogt R. , Schindler R. N.
Published: July 2012

Using a fast flow system with mass spectrometric detection the rate constant at room temperature for the title reaction was determined to be k(4) = 7.5 (±0.8) · 10−11 cm3 molecule−1 s−1. The reaction appears to constitute a convenient dynamic ClO‐source.
On the Mechanism of Methanol Oxidation Sensitized by Anthraquinone
Authors: Kúti Z. , Gál D.
Published: July 2012

The mechanism of photosensitized oxidation of methanol in acetonitrile was investigated in the presence of anthraquinone. Among the main stable products formaldehyde, formic acid, hydrogenperoxide and hydroxymethylhydroperoxide has been found. Their accumulation was measured in the range of 30–60°C. Specific experiments were carried out to prove the existence or negligibility of reactions proposed in the literature. The computer simulation based on literature data and on our results combined with estimation of certain rate coefficients as parameters resulted in good agreement with experimental product accumulation curves. The estimated value of monomolecular decomposition of hydroxymethylperoxyl radical (k325°C ≈ 3 s−1) is in favour of the lowest values that can be found in the literature. In the overall termination process the Russell‐type termination step generally accepted in reactions between peroxyl radicals has decreasing importance with increasing temperature.
The Temperature and Concentration Dependences of Diffusion Coefficients of the Systems Ne–O2, Kr–O2, Xe–O2 and He–NO
Authors: Dunlop Peter J. , Bignell C. M.
Published: July 2012

Diffusion coefficients have been measured for the systems Ne–O2, Kr–O2, Xe–O2 and He–NO at 10 K intervals from 280–320 K. The results differ by as much as 6% from literature values.
Study of the Equation of State of Cyclopentane from 193 to 298 K and Pressures up to 104 MPa
Authors: García Baonza V. , Alonso M. Cáceres , Delgado J. Núñez
Published: July 2012

An expansion apparatus has been used to measure the density of liquid cyclopentane, from 193 to 298 K and pressures up to 104 MPa. The experimental results have been correlated in terms of the Strobridge equation of state, which has been used to estimate several properties of the compressed liquid. Other semitheoretical and theoretical equations of state have been used to predict high pressure results as well as vapor‐liquid equilibrium and second virial coefficients. Comparisons with experimental data are reported in all the cases.
Thermodynamic Investigation of the Pt—Pb Binary Alloys
Authors: Amzil Abdelhamid , Castanet Robert
Published: July 2012

The enthalpy of formation, hf, of the Pt—Pb alloys was measured in the 923–1316 K temperature range with respect to composition by direct reaction calorimetry (drop method) with the help of high temperature Calvet‐type calorimeters. Furthermore we determined also some phase boundaries from the breaks of the hf(x) curves. — The thermodynamic behaviour of the melts is characterized by moderate negative deviations to ideality suggesting some chemical short‐range order (h = −15.88 kJ · mol−1 at 923 K for χPt = 0.53). The associates are very sensible to temperature since the excess heat capacity is positive with a maximum of about 10.2 J · K−1 · mol−1 near χPt = 0.71. Such a behaviour differs strongly from that of the Pd‐Pb system which shows a strongly negative enthalpy of mixing (h = −38.4 kJ · mol−1) without any temperature dependence.
H Atom Formation on Azoethane Pyrolysis
Authors: Klatt M. , Schad I. , Gg. Wagner H.
Published: July 2012

The decomposition of azoethane and the formation of H atoms during its decomposition were measured in shock waves for temperatures between 900 and 2100 K and very low azoethane concentrations. Around 1000 K the formation of H atoms amounts to about 30% of the H atoms expected if azoethane would only dissociate into two ethyl radicals and N2. Towards higher temperatures the H atom yield increases. This can be taken as an indication that the thermal decomposition of azoethane in the temperature range covered cannot only lead to ethyl radicals and N2 but that at least one further reaction channel leading to stable hydrocarbons and N2 must contribute to the reaction.
Reductions of Nitrite and NO on Pt Single Crystal Electrodes in Alkaline Solution
Authors: Ye S. , Hattori H. , Kita H.
Published: July 2012

The reductions of nitrite and nitric oxide (NO) on platinum single crystal electrode were investigated by voltammetric method in alkaline solution. The reductions are very much structure sensitive and proceed exclusively in a potential region of 0.3‐0.5 V (RHE) at pH > 8. Spectrochemical analysis of the electrolyte shows the formation of ammonia with an efficiency of more than 80%. Thus, the overall reaction is concluded as: NO + 5H2O + 6 → NH3 + 7OH−. The present results are discussed in comparsion with other electrochemical results reported.
Kinetic Salt Effects on the Outer‐sphere Electron‐transfer Reaction between Hexacyanoferrate(II) and Pentaammineaquocobalt(III)
Authors: Galán M. , Jiménez R. , Sánchez F.
Published: July 2012

The kinetic salt effects in sodium nitrate solutions, up to 5 mol dm−3, on the reaction between hexacyanoferrate(II) and pentaammineaquocobalt(III) have been studied. The experimental trends of the association constant of the reactants, KIP, and the electron transfer rate constant, ket, can be explained within the framework of dielectric continuum models. – To further support this explanation, the KIP and ket values of the reaction between octacyanomolibdate(IV) and pentaammineaquocobalt(III) in a 0.5 mol dm−3 solution of sodium perchlorate have been determined. – The methodology employed in the present work could be used as a general method for analyzing medium and salt effects on electron transfer processes, when one of the reactants shows irreversible behaviour, from the electrochemical point of view.
Quantum Correlations and Topological Quantum Numbers in the Fractional Quantum Hall Effect
Authors: Brändas Erkki J.
Published: July 2012

It is demonstrated that the fractional Hall plateaux, experimentally observed in some nearly ideal samples at very low temperatures, are manifestations of strongly correlated objects explicitly connected with Coleman's extreme case and Yang's concept of off‐diagonal long‐range order (ODLRO). This interpretation yields (n – 1)/(2n – 1), n = 2,3,… the most stable fractions. The appearance of large even fractions is considered together with a possible explanation of the recently observed fractional Hall states with even numerators in bilayer two‐dimensional electron systems. The present quantum correlations theory also suggests a theoretical analysis of the observed variations in wire‐wound reference resistors.
An Alternating Current Battery
Authors: Schneider Friedemaan W. , Hauser Marcus J. B. , Reising Joachim
Published: July 2012

We built a true alternating current (a.c.) battery that periodically reverses value and sign of its electromotive force (e.m.f.). This a.c. battery is an electrochemical concentration cell that consists of two coupled half cells in which identical oscillating Belousov‐Zhabotinskii (BZ) reactions take place isothermally at 28.0°. The homogeneous BZ oscillations are phase shifted in order to create a potential difference between both half cells. With an increasing load the phase shift between the two half cells decreases (i.e. both oscillations tend to synchronize), consequently the amplitude of the alternating current decreases while the amplitudes of the individual BZ‐oscillators remain unaffected. The e.m.f.‐current diagram of the a.c. battery is analogous to that of direct current batteries. Although the present frequency (period of ∼58 s), current (∼±2.5 μA), e.m.f. (∼±50 mV) and maximum power produced (∼10−7 W) are low it should be possible to construct a.c. batteries with improved performances by the use of other chemical oscillators.
Dependence of the Protonation Constants of β‐Alanine on the Ionic Strength in KNO3 According to Pitzer's Formalism
Authors: Herrero R. , Brandariz I. , Sastre De Vicente M. E.
Published: July 2012

In this work we carried out a simple mathematical analysis of the functions describing the dependence of the stoichiometric acid‐base constant on application of Pitzer's formalism to the activity coefficients of the species involved in two common monoprotonation equilibria. Simulated pK* vs ionic strength plots for two typical acid‐base equilibria AH+2 ⇆ AH + H+ and AH ⇆ A− + H+) are compared with experimental data for the two pK*i of β‐alanine in KNO3 at 25 °C.
Comparison of the Effects of Anionic and Cationic Surfactant on the Precipitation of Calcium Oxalates
Authors: Škrtić D. , Filipović‐Vinceković N. , Bišćan J.
Published: July 2012

Influence of anionic, sodium dodecyl sulfate (SDS) and cationic, dodecylammonium chloride (DDACl) surfactant, on spontaneous batch precipitation of calcium oxalate is investigated. A combination of particle number and size analysis, thermogravimetric analysis, X‐ray diffraction, optical microscopy, electrophoretic and adsorption measurements is used to characterize the processes involved. SDS and DDACl affect the precipitation process at different stages. SDS acts as a nucleation modifier. The action of both surfactants at the stage of primary particle formation exhibits a complex dependence of the rates and mechanisms of crystal growth and aggregation on the structure of aqueous surfactant solutions. Both surfactants inhibit crystal growth and aggregation by adsorption due to the charge and hydrophobic effects. Preferential DDACl sorption on oxalic faces changes the habit of calcium oxalate monohydrate crystals.
The Determination of the Transition State Structure from the J Dependence of the Dissociation Energy E0 (J): The Methane and Ethane Ion Dissociation
Authors: Weitzel Karl‐Michael , Mähnert Joachim , Baumgärtel Helmut
Published: July 2012

A threshold photoelectron photoion coincidence experiment has been setup which allows to measure breakdown curves of energy selected ions at different sample temperatures. These studies reveal the rotational energy of the transition state in unimolecular reactions, which in turn is used as a probe for the transition state structure. According to a model recently suggested this should allow the distinction of tight and loose transition states. The breakdown curves of methane and ethane ions in the region of the lowest reaction channel have been measured at 300 K and close to 0 K. In the case of the H loss from methane ions the shift between these two breakdown curves reveals that the dissociation energy Eo varies significantly with the rotational temperature as expected for a simple bond fission (loose transition state). In the case of H2 loss from ethane ions the shift between the breakdown curves at 300 and close to 0 K shows that E0 (J) does not vary significantly with the rotational temperature. This is to be expected for a concerted elimination reaction (tight transition state).
Determination of Fractal Dimensions of Xerogels via Förster Energy Transfer
Authors: Schleicher J. , Rof M. , Schneider F. W.
Published: July 2012

The fluorescence decay of anthracene and 9,10‐diphenylanthracene in xerogels with various alkyltrimethoxysilane (alkyl = methyl, n‐propyl, n‐octyl) and tetramethoxysilane content is biexponential over a large parameter range. Decreasing degrees of cross linkage as well as lengthening of the alkyl chain lead to an increase of the value and amplitude of the short decay time and finally to a monoexponential decay. The “fractal dimension” of the doped xerogels with monoexponential 9,10‐diphenylanthracene fluorescence is determined via “Förster energy transfer” using rhodamine‐6G as the acceptor. Xerogels of low cross linkage (high content of n‐propyltrimethoxysilane or n‐octyltrimethoxysilane) are characterized by the dimension 3. Further aggregation of the primary silicate clusters leads to a “fractal‐like” network with the dimension of about 2.4.
Experimental Results and Aspects of Analytical Treatment of Vapour Pressure Measurements in Hydrated Melts at Elevated Temperatures
Authors: Boßmann E. , Richter J. , Stark A.
Published: July 2012

Vapour pressures of the hydrated melt systems NaNO3 + H2O, CsNO3 + H2O, (Na0.55,Cs0.45)NO3 + H2O, and (Rb0.40,Ag0.60)NO3 + H2O at 406K, 425 K, 452K, and 491K as a function of the ionic mole fraction are reported. The water activities and the water activity coefficients are computed. All systems investigated show a positive deviation from Raoult's law except the system NaNO3 + H2O which shows within the accuracy of the measurements the behaviour of an ideal mixing. The activity model of Pitzer which is based on the van Laar formalism shows a good representation of the water activity coefficients.
Calorimetric Investigations of Processes at the Solid/Gas Interphase
Authors: Wedler G. , Ganzmann I. , Borgmann D.
Published: July 2012

Adsorption calorimetry, partially combined with thermal desorption spectroscopy and isotope exchange measurements, has been used to study the adsorption and coadsorption of gases on metal films under ultrahigh vacuum conditions. It has proved to be possible to get detailed information on both the primary adsorption step and the consecutive reaction in the adsorbed layer. Adsorption of CO and CO2 on Fe are treated as examples with subsequent decomposition reactions. In the case of the coadsorption of CO and O2 and of H2 and CO on Fe the mutual interaction of the gases including replacement processes are studied.
Surface Reactions of Molecular Hydrogen on Gas‐Phase Deposited Magnesium Oxide
Authors: Hofmann P. , Jacob K.‐H. , Knözinger E.
Published: July 2012

MgO samples with a specific surface area of up to 400 m2/g were prepared by chemical gas phase‐deposition. The resulting samples were used for H2 and D2 chemisorption experiments. IR spectroscopy clearly evidences that homolytic and heterolytic dissociation processes are effective. The corresponding surface centers are radicals (O− and Mg+) and ion pairs MgO respectively. In addition, two isotope exchange reactions on completely different time scales occur between D2 and isolated surface OH groups.
High Temperature in Situ Raman Spectroscopy of Working Oxidative Coupling Catalysts
Authors: Mestl G. , Knözingers H. , Lunsford J. H.
Published: July 2012

Oxidative coupling of methane is an important route to formation of ethane and ethylene. The reaction is catalyzed by a broad range of basic oxides, including lanthanum oxides, that are modified with group IA or group IIA ions. — Laser Raman spectroscopy has been used to characterize surface peroxide structures on La2O3 and Na‐ and Sr‐modified La2O3. These surface peroxide groups are formed on these catalysts by calcination in O2 at temperatures between 500°C and 800°C. By high temperature in situ Raman spectroscopy it was possible to follow the formation of these surface peroxides and their reaction with methane. Changes in the structure and concentration of peroxide groups on the surface of the working catalysts were investigated at elevated temperatures as high as 800°C by varying the partial pressures of the reactant gases. The results provide evidence for the role of peroxide ions for the activation of methane during the oxidative coupling reaction.
A FTIRAS Study of CO Adsorbed at Ni(100) Surfaces
Authors: Lauterbach J. , Wittmann M. , Küppers J.
Published: July 2012

Adsorption of CO at Ni(100) surfaces has been studied with Fourier‐Transform Infrared Absorption‐Reflection (FTIRA) spectroscopy in the temperature range 121 K to 350 K. Up to a coverage of θ = 0.5 top site and bridge site bonded CO has been identified by absorption peaks in the frequency range 2016 to 2048 cm−1 and 1885 to 1949 cm−1, respectively. The site population is temperature dependent, top sites are preferred at high temperatures, bridge sites at low temperatures. Towards the saturation coverage, θ ≈︁ 0.67 the top site peak is replaced by a broad absorption structure between 2000 and 2100 cm−1, which contains at least 3 separate peaks. The bridge site related absorption remains a single peak but shifts upwards by 20 cm−1 to 1968 cm−1. This suggests that above a coverage of θ = 0.5 CO molecules are arranged in an incommensurate adsorption structure, in which a unique top adsorption site does no longer exist.
Kinetics of H2O Adsorption on Clean and Potassium Precovered Ni(111) Surfaces
Authors: Kuch W. , Schulze M. , Schnurnberger W. , Bohwin K.
Published: July 2012

The interaction of water with clean and potassium precovered Ni(111) was studied by X‐ray photoelectron spectroscopy (XPS) in combination with an H2O particle beam for K submonolayer coverages. Equilibrium measurements of the kinetic parameters of the water desorption were performed in the H2O partial pressure range up to 2 · 10−3 Pa. At temperatures between 155 K and 175 K the coverage dependent apparent Arrhenius parameters can be obtained. On the clean surface water adsorbs in a bilayer structure and no dissociation of the water molecules was observed, whereas for potassium covered surfaces a dissociation of approximately one water molecule perpotassium atom and a more complex adsorption behaviour was observed. The apparent Arrhenius parameters for the water desorption on the clean surface and for various potassium precoverages are presented. The different H2O layers are discussed and qualitatively compared with temperature programmed desorption (TPD) measurements.
In‐situ Investigations of the Conduction Mechanisms in Low‐Dimensional Organic Semiconductors and Metals
Authors: Schmeißer Dieter , Göpel Wolfgang
Published: July 2012

We characterize the electronic structure of polypyrrole films and (2,5‐DMe‐Dicyanoquinonediimine)2Ag, Rb single crystals using a combination of electrochemical preparation and electron‐spectroscopical techniques (XPS, UPS, HREELS). These studies allow to characterize the electronic structure, to conclude on the particular conductivity mechanisms for controlled order and structures, and to determine the strength of both, the electron‐phonon and the electron‐electron interactions.
In situ Infrared Spectroscopy at Electrodes: On the Adsorption of CO and CO2 on Copper, Platinum and Gold
Authors: Westerhoff Bernard , Holze Rudolf
Published: July 2012

In situ Infrared reflection absorption spectroscopy RAIRS of adsorbed CO and CO2 on copper, platinum and gold electrodes has been used to study the interaction between adsorbate and electrode and to identify products of reactions following the adsorption. COad on electrochemically roughened copper shows a Surface Enhanced Raman spectrum significantly different from the one recorded with RAIRS, this is attributed to the presence of different adsorption sites probed with these spectroscopies. Reduction of CO2 on platinum results in a CO‐adsorbate with a vibrational behavior different from that of COad.
Probe Beam Deflection for the Analysis of Ion Fluxes at the Solid/Liquid Interface
Authors: Kötz R. , Barbero C. , Haas O.
Published: July 2012

The probe beam deflection (PBD) technique is based on the deflection of a laser beam, aligned parallel to the electrode surface, caused by the concentration profile evolving in front of the electrode during an electrochemical reaction. Monolayer and sub‐monolayer sensitivity has been achieved by means of PBD for (i) the proton flux during oxide formation/reduction on a polycrystalline gold electrode and (ii) for the under potential deposition (UPD) of copper on platinum. The potential of the PBD technique for the analysis of electrochemical reactions is demonstrated for the intrinsic redox reaction occurring on activated glassy carbon (GC) electrodes as a consequence of the generation of surface functional groups. PBD clearly reveals that protons are exchanged in acidic electrolyte on activated GC. Finally, the O2 reduction on Au in alkaline electrolytes has been monitored by the probe beam deflection technique.
Optical In‐situ Methods of High Local Resolution for the Investigation of Corrosion Processes
Authors: Michaelis A. , Schultze J. W.
Published: July 2012

Different optical in‐situ methods which can be combined with standard electrochemistry are discussed. The related methods of micro‐ellipsometry (resolution ca. 40 μm) and micro‐reflection‐spectroscopy (resolution ca. 10 μm) have been added to a well proved laser scanning apparatus (resolution ca. 2 μm), which allows not only probing of sample surfaces but also, by using high laser power, modifying of the layers under investigation. — With these non destructive methods not only new and complement properties are obtained but also local electrode processes in the μm2 scale can be investigated, whereas standard electrochemistry is limited to the mm2 range. — As an example for the application of these methods, the investigation of grain depending passive layer formation on electropolished titanium surfaces is chosen. Herewith predictions about the local corrosion behaviour of this material can be deduced.
Undoped and Doped Oligothiophenes: an In‐situ XPS‐, UPS‐, and HREELS‐Study
Authors: Oeter D. , Ziegler Ch. , Gopel W. , Naarmann H.
Published: July 2012

A new method for doping organic semiconductors is presented. The most common dopant for the widely used α‐sexithiophene (α6T), FeCl3, was co‐sublimed with the oligothiophene under UHV‐conditions. The solid‐state doping effects were studied for systematically varied dopant concentrations in‐situ with XPS. UPS, and HREELS. Up to a doping level of one effective charge per α6T the results can be interpreted as polaron formation. At higher dopant concentrations polaron bands are most probably formed.
In‐Situ Time Resolved Impedance Spectroscopy of Processes in the Solid/Liquid Interface: Electropolymerization of Bithiophene
Authors: Popkirov G. S. , Schindler R. N.
Published: July 2012

Experimental EIS results are presented which were obtained during polymerization of bithiophene on a Pt electrode under potentiostatic conditions. A FFT impedance spectrometer which uses a sum of selected sine waves as a perturbation was employed in this study. A numerical approach was applied to obtain correct impedance data from these measurements. The investigation confirmed that electropolymerization is accompanied by the build‐up of a very large capacitance in the electrode double layer.
Examination of the Time Dependence of Concentration of Defects and Surface States during Intrinsic Redox Processes in Oxide Films
Authors: König U. , Blum O. , Christ R. , Reeh I.
Published: July 2012

Intrinsic redox reactions of oxides are closely related to the electronic properties of the examined systems. Information about the electronic structure can be achieved by examining the potential dependence of the electrode capacity at various polarisation times and potentials. — Redox processes within passive layers on Ni (d < 10 nm) and within LaNiO3 (d > 1 μm) are shown as example of intrinsic reactions. Oxidation as well as reduction starts with the charging of surface states and defects during 100 μs. The redox process of the Ni—O‐matrix needs 10 ms to start. During oxidation, formation of Ni3+ and O2‐evolution takes place. Surface states, formed by Ni3+, covers nearly the whole surface. They will be compensated during O2‐evolution. During reduction, the amount of surface states decreases down to 30% of the surface and the defect number decreases as well. The redox process within LaNiO3 is governed by the reaction of Ni‐ions. It depends strongly on the mobility of vacancies. — The doping of oxides by protons is demonstrated for passive layers on Ti. During polarisation near Ufb (reduction), protons penetrate into the layer and the donor number increases. Polarisation at anodic potentials (oxidation) forces the protons out of the layer. During the redox process, no change of the oxide takes place and surface states can be neglected.
In‐situ Investigation of Electrochemical Alloy Formation, Electroless Metal Deposition, and Selective Alloy Oxidation
Authors: Pittermann Udo , Weil Konrad G.
Published: July 2012

Examples will be presented for applications of the following in‐situ techniques: determination of mass changes with a quartz microbalance, determination of double layer properties with a fast impedance spectroscopy, and determination of surface microstructures from impedance analysis of vibrating quartz crystals. These examples are: Formation of copper/gold alloys from underpotential layers of copper on gold, electroless copper deposition with formaldehyde, and selective oxidation of copper/gold alloys.
Ion Movements during Redox Switching of Polypyrrole — Experiment and Simulation
Authors: Heinze JüRgen , Bilger Ralf
Published: July 2012

Oxidation of pyrrole yields a charged polymer film with incorporated anions. During the following reduction electroneutrality can be maintained by expulsion of these anions or by incorporation of cations. The contribution of both processes to the overall charge transport is found to depend strongly on the formation potential during polymerization. The redox process of polypyrrole formed at +1.0 V vs. Ag/AgCl is accompanied by a change in mass, which can be interpreted by a simultaneous transport of anions and cations. A lower formation potential leads to a separation of the charge transport in an either anion or cation dominated region. These differences are related to a cathodically shifted first reduction which occurs if a low formation potential was used. The charge transfer at the electrode and at the polymer‐solution interface is illustrated by a physical model. It consists of an (E)n—C—(E)m mechanism for the redox behavior of the polymer and a first‐order reaction for incorporation and expulsion of ions. Computed voltammograms and mass curves are presented for different situations and compared to experimental conditions.
Rate Constants for the Reactions of CH2 (X̄3B1) with Selected Alkenes at Temperatures Between 296 K≤T≤728 K
Authors: Kraus H. , Oehlers C , Temps F. , Gg. Wagner H. , Wolf M.
Published: July 2012

The kinetics of the reactions of CH2 (X̄3B1) with selected alkenes R = ethylene (1), tetramethylethylene (2), cycloheptatriene (3), and 1,3‐butadiene (4) were studied at temperatures between 296 K≤T≤728 K. Rate constants were measured for reactions (2–4) using the discharge flow technique with Far‐Infrared Laser Magnetic Resonance (FIR–LMR) detection of 3CH2. The experimental data can be described by the rate expressions (±2σ)magnified image These data and results for reaction (1) obtained earlier were analyzed to separate the contributions to the CH2 (X̄) depletion by reactive channels versus collisional excitation to the ã1A1 state of CH2 followed by reactions of CH2 (ã). The rate expressions (±2σ) for the reactive pathways of CH2 (X̄) were found to be magnified image.
Rayleigh‐Brillouin Scattering of Molten ZnCl2
Authors: Zhu Hongmin , Sato Yuzuru , Yamamura Tsutomu , Sugimoto Katsuhisa , Sato Yoshiyuki
Published: July 2012

The Rayleigh‐Brillouin scattering experiment has been carried out for molten ZnCl2. The complete profiles of Rayleigh‐Brillouin spectra were obtained at scattering angles of 90° and 140°, and at temperatures ranging from 550 to 1000 K by the use of the carefully purified samples. The remarkable change in the shape of the spectrum with temperature variation has been observed and has been concluded to be due to a structural relaxation in the melt. The spectra have been analyzed by the viscoelastic theory on the assumption of a single relaxation. The sound velocities at the limiting low and high frequencies and the relaxation time have been determined.
Static Relative Permittivity of Carbon Dioxide and Nitrous Oxide up to 30 MPa
Authors: Moriyoshi T. , Kita T. , Uosaki Y.
Published: July 2012

The static relative permittivity εrof carbon dioxide and nitrous oxide has been measured in a temperature range from 273.15 to 353.15 K at pressures up to 30 MPa. The measurements were performed by means of a transformer ratio‐arm bridge with a three‐terminal capacitance cell installed in a pressure vessel at frequencies between 10 to 50 kHz. The newly‐designed capacitance cell and pressure apparatus are described. Experimental εr‐values obtained for the two fluids were estimated to be accurate to within ±0.02%. The critical relative permittivity εr,C, evaluated from the εr‐values of coexisting saturated vapor and saturated liquid, was 1.267±0.001 for carbon dioxide and 1.288±0.003 for nitrous oxide. The density dependence of the εr‐values can be expressed by a quadratic function of density, independent of temperature. The εr‐data for each fluid were combined with available densities from the literature to calculate the molar polarizationPmgiven by the Clausius‐Mossotti (CM) equation. Some consideration is given for the coefficients of the dielectric virial equation, i.e., the expansion of the CM equation in powers of density.
1H NMR Study of Molecular Motions and Phase Transitions in Methyl Ammonium Hexabromo Selenate [(CH3NH3)2SeBr6]
Authors: Murthy B. V. S. , Ramesh K. P. , Ramakrishna J.
Published: July 2012

The temperature dependence of 1H spin‐lattice relaxation time, T1, and that of the second moment, M2, are analysed in the temperature range 390 K to 77 K. A plot of T1 vs inverse temperature shows three phase transitions at 250 K, 167 K and 111 K. At 167 K, T1 displays a large jump while it shows changes in slope at 250 K and 111 K. In the high temperature phase (> 167 K), the correlated motion of CH3 and NH3 groups is found to cause the relaxation while their uncorrelated motion takes over in the low temperature phases (< 167 K). The unusual T1 behaviour in phase II (250 K‐167 K) is ascribed to the small angle torsion of the cation. A constant M2 value of ∼ 9.7 G2, throughout the range of temperature studied, indicates the presence of reorientation of CH3 and NH3 groups.