Robert Schiller

Mobility of localized and quasifree excess electrons in liquid hydrocarbons

The dependences of excess electron mobility on temperature and conduction state energy in saturated liquid hydrocarbons are measured in order to evaluate the mobilities in the localized and in the quasifree state and the energies of the localized state. These quantities appeared earlier as adjustable parameters of a two‐state electron model. Localized electron mobility is described in terms of the motion of a microscopic bubble. The transport of the quasifree electrons is regarded as that of a plane wave scattered by density fluctuations of the liquid. This model, combined with the mobility equation of Cohen and Lekner, finds reasonable agreement with experimental values which vary between 34 and about 400 cm2 V−1 sec−1.

Diffusion kinetics at fractal electrodes

Abstract Rough, porous or partially active electrodes are often modelled as fractals and the laws of electrode kinetics are derived accordingly. The theories dealing with diffusion-controlled currents towards fractal interfaces are surveyed and their applicability to real rough electrode surfaces is discussed.

Concentration‐dependent diffusivity: Hydrogen percolation in WO3

The diffusivity of H in a thin layer of WO3 was measured optically through the visible optical absorption of the H‐containing substance. Microdensitometry and the photoresist technique made a 1‐μm lateral resolution available. When the data were evaluated by Boltzmann’s method, the diffusion coefficient, as low as about Dm ≊10−11 cm2/sec at high H concentrations, was shown to increase sharply with decreasing H content. This behavior was quantitatively understood in terms of a percolation model modified by assuming H atoms to jam fast channels. The extreme low‐concentration diffusion coefficient D0 was evaluated by virtue of this model and gave D0≊10−9 cm2/sec.

Percolation model of electron and hole mobility in liquid mixtures

The theory of charge percolation, originally developed for inhomogeneous mixtures of metals, is transformed to describe mobility of electrons and holes in homogeneous liquid mixtures. Systems in which the energies of the charge carriers are independent of composition are expected to obey the predictions of this formalism. Here concentration fluctuations act as microscopic inhomogeneities. As examples, hole mobility in trans‐decaline–cyclohexane, and electron mobility in hexafluorobenzene–benzene and in n‐hexane–ethanol mixtures are treated. The number of molecules interacting with a charge carrier appears as an important parameter. Mobility versus concentration curves are calculated in the entire concentration range and are in good agreement with observations. Finally a method is proposed for estimating electron mobility in hexafluorobenzene.

Behavior of Ion Spurs and Tracks in Irradiated Dipolar Systems

The problem of electron moderation and subsequent recapture or escape in irradiated dipolar substances is investigated theoretically. By considering the dielectric relaxation, the electric energy of a spur or track consisting of positive ions and diffusing electrons is evaluated. The moderation being fast as compared with the dielectric relaxation time, the energy content of the spur or track decreases due to an increase in the dielectric constant after the moderation has been completed. At the expense of this energy decrease, some thermalized electrons may diffuse away from the field of the positive ions if they are slow enough not to increase the spur energy faster than it is decreased by dielectric relaxation. The theory is tentatively applied to γ and α‐irradiated water and ice and, while a substantial fraction of electrons is found capable of escaping in the liquid state, for the crystalline state complete recapture is predicted.

Continuous-time random-walk theory of interfering diffusion and chemical reaction with an application to electrochemical impedance spectra of oxidized Zr–1%Nb

A microscopic theory is developed for the interplay of diffusion and chemical reaction and the results are compared with electrode impedance measurements on an oxide electrode. The theory is based on the ideas of continuous-time random walk and accounts for the interference of diffusion and recombination of the charge carriers in the oxide. The treatment results in a dispersive diffusivity with two time constants, one of them corresponding to the random walk, the other to the reaction. Combining this diffusivity with the Warburg electrode admittance expression, which refers to cases where the rate-limiting step is diffusion in a semi-infinite medium bounded by a plane, an admittance function is obtained. The phase angle is found to be higher than 45 degrees distinguishing it from the Gerischer impedance which was developed for a related problem. The oxides were produced by hydrothermal oxidation of Zr-l%Nb alloy, a metal used as cladding material for nuclear fuel elements. The electrode impedance spectra of Zr/Zr-oxide electrodes in aqueous SO(3) (2-) solutions were taken at various anodic voltages between 1 Hz and 100 kHz and temperatures between 278 and 333 K. The theoretical admittance functions could be successfully compared with the observed spectra. Both the functional forms and the fitted parameter values support our theory which is also in keeping with Macdonalds point-defect model.

The effect of mechanical stress on the potential of the Ag/Ag+ electrode

The effect of mechanical stress, σ, on electrode potential, E, was studied under zero current conditions. Silver wires in contact with AgNO3 solutions were exposed to tensile stress and the variation of the potential was measured in a two-electrode cell. The change in the steady state, ΔE, was found to be proportional to σ whereas the time dependence, E(t), could be reasonably described by an exponential function. The ΔE s. σ functions were understood in terms of the electrostatics of the double layer enabling one to evaluate the stress dependence of the potential of zero charge, (∂E0/∂σ) = 25.6 ± 1 μV MPa−1; this experimental value is supported by a theoretical estimation.

Ion-electron pairs in condensed polar media treated as H-like atoms

A model of radiation produced ion–electron pairs with an electron energy below about 1 eV is proposed for the description of electron moderation, self‐trapping, and escape in condensed polar media. A discrete ion–electron pair is regarded as a ground‐state H‐like atom which interacts with the medium through polarization forces and by experiencing energy fluctuations. Slowly relaxing polarization makes electron energy decrease on the time scale of constant‐charge dielectric relaxation. A strongly attracting polarization well is formed immediately upon ion pair formation owing to instantaneous polarization. Energy fluctuations can make the electron escape from the field of the ion, but not from that of the polarization well, i.e., the electron is already self‐trapped when moderation and escape take place. The rate of electron moderation was found to agree with earlier estimates made by Frohlich and Platzman. Solvated electron yields, by allowing also for initial recombination of energetically independent io...

Quasipercolation: Charge transport in fluctuating systems

Mobility of charge carriers in certain liquid systems is controlled by temporal fluctuations in local conductivity. Fast transport proceeds along high mobility regions similarly to traditional percolation with the difference that these regions form and fade away with fluctuations. By making use of the idea of waiting time distribution of continuous time random walk, formulas for relative mobility as a function of the expectation value of proportion of high mobility regions are suggested. The results compare reasonably well with experimental data. Under the experimental conditions given quasipercolation theory and the effective medium theory of traditional percolation do not differ too much numerically. For site percolation threshold in nonfluctuating systems the expression [(e−1)/ez]1/2 is suggested, where e is the base of natural logarithm and z is the coordination number.

Electron mobility and conduction state energy in hydrocarbon mixtures

Abstract The energy of the conduction state, V 0 in two-component hydrocarbon mixtures was measured by photo-injection. The effective medium model and the partial localization model were used to calculate electron mobility as a function of V 0 . Both theories agree reasonably with the experiments.