bluuebunny/crossref_metadata_2025_split huggingface dataset:
Theory. Relaxation Dynamics in Disordered Ionic Conductors
Authors: Dieterich W. , Knödler D. , Petersen J. 
Published: July 2012

AbstractA microscopic mechanism for understanding fractional power‐laws in the ac‐response of ionic conductors is discussed in terms of hopping of charged particles in disordered lattices. We review recent Monte‐Carlo simulations for lattices with Gaussian disorder in the local site energies, which show that “anomalous diffusion” occurs at intermediate time‐scales as a result of the interplay of Coulomb‐interactions and structural disorder. A new model pertaining to ionic transport in oxid glasses is proposed, which emphasises the role of long‐range Coulomb‐potentials due to counter‐ions. Implications with respect to other dynamic probes e.g. inelastic neutron scattering and ultrasonic attenuation are also briefly discussed.
Anomalous a.c. Response due to Jump Diffusion in Disordered Materials
Authors: Wagener Michael , Schirmacher Walter 
Published: July 2012

AbstractThe a.c. response due to jump diffusion in systems with fluctuating energy barriers is calculated in effective medium approximation. The crossover from a frequency independent to a frequency dependent a.c. conductivity is shown to be related to a transition from normal to anomalous diffusion. To extract the non‐analytical frequency dependence of the dynamic conductivity for ω → 0 we study the loss function which – depending on the use of the proper local Green's function in the EMA equation – reveals a √ω dependence in the region of normal diffusion as it should. The loss function looks like ω−α with 0 < α < 1 in the region of anomalous diffusion, but the details of the frequency dependence are different for different models, i.e. the curves are non‐universal.
A Target Diffusion Theory for Nuclear Spin Relaxation in Ionically‐Conducting Glasses
Authors: Elliott S. R. , Owens A. P. 
Published: July 2012

AbstractA theoretical mechanism is presented for nuclear spin relaxation in ionically‐conducting glasses (or disordered crystals) caused by ionic motion. This is based on the diffusion‐controlled relaxation model previously used to account for electrical relaxation in such materials: relaxation is assumed to occur at particular (interstitialcy) sites, triggered by the arrival of other diffusing ions. The experimental dependence of the spin‐lattice relaxation rate on temperature and ionic concentration can be understood on the basis of this model.
Transport Coefficients of Liquid Benzene by Molecular Dynamics Calculations
Authors: Luo H. , Hoheisel C. 
Published: July 2012

AbstractWith a 6‐centre Lennard‐Jones potential, we have studied thermal collective transport coefficients of the benzene model liquid by molecular dynamics (MD) calculations. Shear and bulk viscosity as well as thermal conductivity were determined for 8 different states of liquid benzene. Agreement between experimental values and MD results is surprisingly good for the shear viscosity and thermal conductivity. Unfortunately there are no experimental data available for the bulk viscosity. In the wider neighbourhood of the triple point of benzene, the time correlation functions for the shear and the bulk viscosity were found to have an extreme form, namely an initial short‐time decay within 0.5 ps followed by a long positive branch of very small amplitude up to about 4–6 ps. A comparable long time behaviour was also found in the reorientational correlation functions.
Molecular Dynamics Simulations of the Depolarized Rayleigh Spectra of CS2/CCI4 Liquid Mixtures
Authors: Stassen H. , Dorfmüller Th. 
Published: July 2012

AbstractMolecular dynamics simulations were used to calculate the depolarized Rayleigh light scattering spectra of CS2/CCI4 liquid mixtures at 298 K modelling the intermolecular interactions by atom‐atom Lennard‐Jones potentials. Approximating each molecule as a point scatterer these spectra were obtained using the dipole‐induced dipole mechanism for the interaction‐induced polarizability. Intensities and lineshapes of the first‐order perturbation theory for the system polarizability of this model are compared to the exact all‐order results. The agreement of both models with experimental spectra is in some respects satisfactory, but also displays characteristic deviations.
Fractal Aspects of Superionic Conductors
Authors: Den Hartog H. W. , Ebens W. O. , Dorenbos P. 
Published: July 2012

AbstractIn this paper we will discuss the properties of a group of fluorite type superionic materials, which has been studied in detail in our laboratory. Some of these materials, which are denoted by A1‐xRxF2+x, can be considered as model materials for the description of extrinsic superionic conductors. We will concentrate mainly at the series of cubic solid solutions consisting of strontium and cerium fluoride. For small and moderate Ce concentrations the dominant defects in these materials are dipolar systems and consequently these defects are expected to play an important role in the conduction processes. – We have found strong evidence for percolation conduction if the concentration of the trivalent impurities is about 4 mol%. In the vicinity of this concentration the ionic conductivity increases sharply as a function of the concentration, while the dielectric constant reveals a maximum. The experimental results can be explained by assuming that the conductivity at concentrations close to and above the percolation threshold is governed by the easy jumps of interstitial fluoride ions in the vicinity of trivalent ions. We know from dielectric spectroscopy experiments, that these jumps occur with a rather small activation energy. At first sight the above mentioned concentration might be far to low, but one should realize, that the easy jumps take place in a relatively large area surrounding the trivalent impurity. Considering the geometry of the dipolar defects, however, one expects a percolation threshold of a few mol%.
Frequency‐Dependent Conductivities of RbAg4I5 and Na‐β″‐Alumina from Radio to FIR Frequencies
Authors: Hoppe R. , Kloidt T. , Funke K. 
Published: July 2012

AbstractThe electric conductivities of the two fast ionic conductors RbAg4I5 and Na‐β″‐alumina have been determined at various temperatures and frequencies from 4 MHz to 105 GHz. – The conductivity of RbAg4I5 is found to display a dispersion as expected by the so‐called “universal dynamic” response, a high‐frequency plateau in the range of 100 GHz and an Arrhenius behaviour at both low and high frequencies. – The spectra of Na‐β″‐alumima show a different behaviour. In addition to the “universal dynamic” response dispersion, a faster and thermally less activated relaxation process is observed at high frequencies and low temperatures. Up to 60 GHz, a high‐frequency plateau has not been encountered.
Impedance and 2H‐NMR Studies of Stoichiometric Alkaline Hydroxide Hydrates
Authors: Borkowska Z. , Frese U. , Kriegsmann E. , Stimming U. , Gavish M. , Adamic K. J. , Greenbaum S. G. 
Published: July 2012

AbstractHydrates of the alkaline hydroxides LiOH, NaOH, KOH and CsOH in their liquid and solid states were investigated using impedance spectroscopy. KOH · 4H2O was studied using deuteron NMR. From the impedance measurements the electrical conductivity of the hydrate was evaluated. It is an important result of these measurements that the lithium and sodium hydroxide hydrates exhibit a poor conductivity in the solid state; the activation energies of conductivity exceed 3 eV. The potassium and cesium hydroxide hydrates, however, are considerably more conductive in the solid state, especially at low temperatures with activation energies around 0.7 eV. Linewidths and T1 and T2 relaxation times were determined as a function of temperature in the liquid and solid hydrate. The NMR measurements indicate that the protons (deuterons) are the mobile species. The differences in conductivity may be due to a size effect of the cation in that large cations with a single charge favor an extended water network which maybe of clathrate‐like structure.
The Double α‐Peak Phenomenon in Polymers
Authors: Hofacker I. , Fuchs M. , Latz A. 
Published: July 2012

AbstractWe discuss the structure of the α‐peak in some high molecular weight polymers. A double α‐peak phenomenon appears as a generic feature of the mode coupling theory related to the self crossing of transition hypersurfaces. A schematic three component model is solved to fit quantitatively dielectric loss spectra of poly propylene glycol.
Investigation of Complex Intramolecular Motion in Supercooled Liquids
Authors: Pösch M. , Althoff G. , Killie S. , Wenning E. , Hertz H. G. 
Published: July 2012

AbstractAfter a brief résumé of the Woessner theory which treats nuclear magnetic relaxation effects caused by internal and anisotropic motion of molecules in liquids we present proton magnetic relaxation rates of specifically deuterated molecules possessing an interacting group (–OH or –COOH) and a hydrocarbon chain of increasing length, namely methanol and acetic acid, ethanol and propionic acid, n‐propanol. Measurements were done in the range from room temperature to ∼ 15 K. Various interacting substances were added to slow down the movement of the interacting group relative to the internal molecular motions, yielding respective experimental manifestations. Some brief hints are given to show the shortcomings of the Woessner theory.
Diffusion of Positive Muons in Niobium Doped with Titanium
Authors: Fell H.‐J. , Hempelmann R. , Hartmann O. , Harris S. , Wäppling R. 
Published: July 2012

AbstractThe diffusional behaviour of positive muons in bcc NbTi with three different titanium dopings (0.1, 0.5, and 1.0 at%) was studied using muon spin relaxation both in transverse magnetic field and in zero field. The temperature range 2 to 200 K was covered in these experiments. The temperature dependence of the muon spin depolarization rate indicates the existence of different motional states: i) below 15 K the muons are localized somewhere in the lattice at Nb4 tetrahedral sites due to random strain fields; ii) between 20 and 50 K some of the muons are trapped at substitutional Ti atoms where they perform a rapid localized motion over four or six adjacent Nb3Ti sites; iii) in the same temperature range other muons are trapped at residual interstitial oxygen and nitrogen impurities (185 ppm); iv) between 80 and 150 K the muons appear to extend their localized motion to 24 adjacent Nb3Ti sites; v) eventually, above 200 K, we observe long range muon diffusion. The distinction between a diffusing muon and a muon performing a rapid localized motion over several sites is possible by examining the long time behaviour of the muon polarization function in zero field.
Light and Neutron Scattering Complex Relaxation Behaviour in Glass Forming Liquids from Brillouin Scattering
Authors: Quitmann D. , Soltwisch M. , Loheider S. 
Published: July 2012

AbstractPropagation and damping of thermal longitudinal acoustic sound waves can be studied in detail by inelastic light scattering. We concentrate here on inorganic network glassformers. Relaxation leads to shifts of the Brillouin lines, and to deviations from Lorentzian shapes which may become very large (ZnCl2). From the shift and broadening, the relaxation and its time dependence or the relaxation time distribution, can be determined. The analysis is based on viscoelastic theory for density fluctuations. The method of analysis and the underlying assumptions are discussed. While the experimental precision is good, the largest drawback of Brillouin scattering is its restricted dynamical range. The difficulty of deciding unambiguously between single‐τ or complex relaxation from Brillouin spectra is discussed. An example (GeSBr2) where reasonably large ranges of frequency and temperature have been covered in a recent experiment, is used to demonstrate the combined effect of α‐ and β‐relaxation processes on LA Brillouin lines.
The Dynamic Structure Factor of Expanded Liquid Rubidium
Authors: Pilgrim C. , Winter R. , Hensel F. , Morkel C. , Gläser W. 
Published: July 2012

AbstractBy inelastic neutron scattering, the coherent dynamic structure factor S(Q, ω) of expanded liquid rubidium has been measured up to about 1700 K using the IN6 spectrometer at the Institut Laue‐Langevin, Grenoble. The scattering law S(Q,ω) has been determined for energy transfers from −3.5 to 20 meV in the momentum transfer region from 0.55 Å−1 to 2.6 Å−1. The existence of collective density excitations at short wavelength and high frequency for the expanded liquid metal is discussed and the Enskog self‐diffusion coefficient is evaluated from the experimental data.
Quasielastic Neutron Scattering from RbAg4I5 Single Crystal Gives Evidence of Jump Relaxation
Authors: Wilmer D. , Funke K. , Kloidt T. , Carlile C. J. 
Published: July 2012

AbstractA quasielastic neutron scattering experiment has been performed on a single crystalline sample of the fast ionic conductor rubidium silver iodide (RbAg4I5) in order to study the dynamics of the mobile silver ions in this material. The corrected spectra show broad quasielastic components whose weight increases with increasing momentum transfer in the elastic Q‐range from 1.0 to 1.8 Å−1. The quasielastic broadening is explained by the frequent occurrence of so‐called forward‐backward hopping sequences of the silver ions which are key steps of jump relaxation. A calculation based on the jump relaxation model yields a normalized frequency spectrum of the silver hopping motion that simultaneously fits the dynamic structure factor and the dynamic conductivity spectra of this material.
Search for Quasielastic Neutron Scattering Components Due to Jump Relaxation in Glass
Authors: Cramer C. , Funke K. , Vortkamp C. , Dianoux A. J. , Grüne R. 
Published: July 2012

AbstractA lithium bromide doped lithium borate glass has been studied by neutron scattering experiments and by measurement of the dynamic conductivity. Whereas the dispersion of the dynamic conductivity at lower frequencies can be interpreted in terms of a non‐Debye jump relaxation model, a quasielastic neutron scattering component, as predicted by the model, could not be resolved. However, in some other glassy systems there is evidence of quasielastic components due to jump relaxation processes. This is shown for two examples: the glass forming melt 3KNO3 · 2Ca(NO3)2 and an AgI · AgPO3 glass.
Dynamic Anomalies and their Relation to the Glass Transition: A Neutron Scattering Study of the Glass Forming Van der Waals Liquid Ortho‐terphenyl
Authors: Bartsch E. , Debus O. , Fujara F. , Kiebel M. , Sillescu H. , Petry W. 
Published: July 2012

AbstractNeutron scattering experiments on the molecular glass former ortho‐terphenyl reveal a dynamic anomaly at a temperature Tc ≈ 290 K well above the calorimetric glass temperature Tg = 243 K. Close above Tc the density autocorrelation function ΦQ(t) shows a two step decay over 4–5 decades in time. The slower component obeys the time‐temperature superposition principle. Its line shape can be well parametrized by a Kohlrausch law and is strongly temperature dependent as its relaxation time scales with the shear viscosity. Thus this component is identified with the structural relaxation (α‐process). The faster component (β‐process) is much less temperature dependent. Its line shape factorizes in a purely Q‐dependent and a purely time‐dependent part and its time scale follows a power law with a critical exponent a. The crossover region between the α‐and ß‐process follows a power law (von Schweidler law) with a critical exponent b. Approaching Tc from below the plateau value separating the α and the β process (= Debye‐Waller factor) shows a critical decrease and bends over to a weak temperature dependence at Tc. These findings support several predictions made by the mode coupling theory of the glass transition which relates these dynamic anomalies to remnants of an ideal glass transition.
An Investigation of the Reaction of CH3 Radicals with O2 at High Temperatures
Authors: Klatt M. , Röhrig M. , Gg. Wagner H. 
Published: July 2012

AbstractThe reaction of CH3 radicals with O2 was investigated behind incident shock waves at temperatures between 1400 and 2300 K and total densities between 2 · 10−6 and 8 · 10−6 mol/cm3. The formation of O and H atoms was followed by atomic resonance absorption spectroscopy (ARAS) at 130.5 nm and 121.6 nm. A rate constant of 2.3 · 1013 exp(–15400 K/T) cm3/mol s for the reaction CH3 O2 + CH3O + O was determined.
An Investigation of the Reactions of NO3 Radicals with Cl and ClO
Authors: Becker E. , Wille U. , Rahman M. M. , Schindler R. N. 
Published: July 2012

AbstractThe reaction (1) Cl + NO3 → ClO + NO2 was studied at 298 K by observing the kinetic behaviour of NO3, Cl and ClO using discharge‐flow mass‐spectrometric technique. A rate constant k(1) = (2.26 ± 0.17) · 10–11 cm3 molecule−1 s−1 was obtained. The secondary processes between NO3 and ClO were also investigated and OClO was detected as a reaction product. For the rate constant of the reaction (2a) ClO + NO3 → ClOO + NO2 an upper limit of k(2a) = 1 · 10−13 cm3 molecule−1 s−1 was found. In contrast to previous findings it is shown that reaction (2b) ClO + NO3 → OClO + NO2 is the predominant channel with k(2b) = (4.3 ± 1.0) · 10−13 cm3 molecule−1 s−1.
Untersuchungen zur Adsorptionskinetik von Phenolen, Diphenolen und cyclischen aliphatischen Alkoholen mit der Methode des schnellen Elektrolytaustausches
Authors: Janoske Gido , Hamann Carl Heinz 
Published: July 2012

AbstractThe determination of thermodynamic and kinetic data of reactive chemisorption of organic molecules with an improved technique is described. It substitutes a rapid electrolyte exchange with potential control of the working electrode for an electrode transfer. The degree of coverage, rate of adsorption and interaction between adsorbate molecules from cyclic voltamograms recorded after adsorption and electrolyte exchange was determinated. The adsorption of Phenols, Diphenols and cyclic aliphatic alcohols on a platinum electrode in contact with an acidic electrolyte solution is studied. The adsorption rate of the phenolic compounds is very fast in reference to the corresponding cyclic alcohols. This effect can be explained by the strong chemisorption of aromatic π‐bonded species to the platinum surface. With the exception of Pentafluorphenol the interaction between the adsorbate molecules for all substances is similar and can be described as low repulsion.
Phasenzusammensetzung und Sauerstoffaktivität oxidischer Katalysatoren im Betriebszustand
Authors: Hildenbrand H.‐H. , Lintz H.‐G. 
Published: July 2012

AbstractSolid electrolyte potentiometry (SEP) has been used to measure the oxygen activity in the catalyst during the oxidation of propene on copper oxides. The combined kinetic and potentiometric measurements have shown that SEP can be extended to oxidic catalysts prepared in an adequate fashion. The strong correlation between the phase composition of copper oxide and the formation of acrolein proves the applicability of the potentiometric method to monitor phase transitions of catalysts under working conditions.
Homogenization of Water/Chloroform and Water/n‐Butanol Mixtures with Tetraalkylammonium Halides. Phase Diagrams and Properties of the Homogeneous Phases
Authors: Geyer Claus , Mahr Michael , Paulus Helmut , Weil Konrad G. 
Published: July 2012

AbstractWe report on two ternary systems with a ternary miscibility gap. They consist of two immiscible solvents (water and chloroform or water and n‐butanol) and salts which can close the miscibility gap. These salts are unsymmetrical tetraalkylammoniumhalides R3R'N+X− (X− = Cl−, Br−, I−). We determined the binodal curves in the ternary phase diagrams. In the homogeneous region, we measured densities, kinematic viscosities, and electrical conductivities. At constant mole fractions of salt, the viscosities increase and reach constant values while the conductivities decrease monotonously with increasing mole fractions of the organic solvent. Addition of salt to a given mixture of the solvents leads to a monotonous increase of the viscosities while the conductivities first increase, then go through maxima and decrease again. By X‐ray analysis we determined the crystal structure of methyl‐tri‐n‐propylammonium iodide. The lattice is triclinic, space group P1. A ternary compound, containing the salt together with chloroform and water could also be prepared. The crystal is disordered at room temperature, a skeleton of tetraalkylammonium ions is present which contains channels. In these channels, chloroform and water molecules seem to be mobile. The X‐ray analysis shows no special positions for these solvent molecules. The structure of this compound does not indicate heteroselective solvation. This concept therefore should not be used in the discussion of the homogenization by these salts.
Vapor‐Liquid Equilibria of Mixtures of Methyl Butanoate + Propan‐2‐ol at 74.66, 101.32, and 127.99 kPa
Authors: Ortega J. , Susial P. 
Published: July 2012

AbstractVapor‐Liquid equilibrium data for binary system methyl butanoate + propan‐2‐ol were measured by a dynamic phase equilibrium apparatus at three different pressures of 74.66, 101.32 and 127.99 kPa. An azeotrope was found at low ester concentration, which decrease with the increase of the working pressure. In all cases studied, p‐T‐x‐y data exhibit a positive consistency being correlated through a suitable equation. Good predictions are obtained by ASOG [1] and UNIFAC [2, 3] methods and employing parameters corresponding to different alkanol/ester interactions. The mean overall errors for activity coefficients were smaller than 8% as expected.
SAXS Studies on Structure Formation in Microemulsion‐Triblock Copolymer Systems
Authors: Hilfiker Rolf 
Published: July 2012

AbstractSmall angle X‐ray scattering (SAXS) measurements were performed on water/AOT (sodium di‐2‐ethyl‐hexylsulfosuccinate)/i‐octane(2,2,4‐trimethylpentane) w/o‐microemulsions with various amounts of block‐copoly(oxyethylene/isoprene/oxyethylene). Addition of copolymer causes an aggregation of the microemulsion droplets. The first aggregation step is the formation of dimers (two droplets connected by a copolymer molecule). From the experimental form factors, structure and size of the dimers could be calculated. In particular, we could show that the radius of the droplets increases by about 10% after absorbing a copolymer block. The distance between two droplets and the width of the distance distribution were determined as well. From the decrease of the number of free nanodroplets as a function of the amount of copolymer it could be concluded that roughly one in four copolymer molecules acts as a bridge between two droplets.
Behaviour of Helical Pitch in Cholesteric and Chiral Smectic C* Phases
Authors: Bahr Ch. , Escher C. , Fliegner D. , Heppke G. , Molsen H. 
Published: July 2012

AbstractSeveral nonchiral liquid crystals exhibiting nematic and smectic C phases have been doped with different chiral compounds. The handedness and the pitch of the induced helical structures were determined in both phases. Whereas some chiral dopants induce helical structures which, as to be expected, possess the same handedness in all matrices and phases, we found that in some cases the same dopant induces helical structures of opposing handedness in different nematic matrices. Moreover, it was observed that the helical sense in the chiral smectic C* phase can be opposite to the helical sense in the chiral nematic phase of the same liquid crystal system. The dependence of the helical structures on the composition was studied in several quasi‐binary diagrams.