Lawrence Slifkin

Seismic electric signals from displacement of charged dislocations

Abstract One possible mechanism for the generation of seismic electric signals is the displacement of segments of charged dislocations, responding to changes in the applied stress. Using information available from the study of simpler ionic crystals, a crude estimate is made of the voltage that could be generated from large blocks of the Earths crust during a pre-earthquake stress adjustment. Within the many uncertainties of critical parameters, the results are consistent with the magnitudes of precursor signals that have been observed in Greece.

Ionic conductivity of mixed silver halide crystals

Abstract To evaluate the effects of mixed halides on the lattice defect parameters of the silver halides, we have measured the ionic conductivity both of the entire range of mixed AgBr-AgCl single crystals, aftd also of several iodide-doped crystals. For the AgBr-AgCl system, the intrinsic conductivity at a given temperature decreases monotonically from pure AgBr to pure AgCl. The deduced Frenkel defect formation energy varies only a little from 0 to 50 mole % AgCl, and then increases rapidly with further increase in AgCl content, closely paralleling the ratio of bulk modulus to dielectric constant. The defect formation energy in these crystals hence reflects the average macroscopic properties of the solid solution. For the iodide-doped crystals, however, the results are quite different. Small amounts-of iodide cause large increases in the conductivity of AgBr andiAgCl, especially in the latter. These results suggest that the elastic strain introduced by the oversized iodide ion exerts an appreciable local effect on the Frenkel defect formation, in contrast to the crystal-averaged response found for the AgBr-AgCl solid solutions. Furthermore, the Arrhenius plots for the conductivitiei of the AgBr: I specimens show curvature which suggests a temperature-dependent pairing of the solute.

A study of the high-temperature transport anomaly in AgBr, by diffusion of sodium tracer☆

Abstract A detailed measurement of the temperature dependence of the tracer diffusivity of substitutional sodium ion in AgBr indicates the activation energy for the formation of a Frenkel pair to be temperature-dependent. The approach used earlier by Muller and by Aboagye and Friauf in interpreting the “extra” ionic conductivity at high temperatures as due to an anomalous increase in the defect concentrations thus appears to be essentially correct. However, the decreases in defect formation enthalpy at high temperatures, as deduced from these diffusion experiments, are somewhat smaller than those obtained earlier from conductivity data. Also, the activation enthalpy for the jumping of a sodium ion into a neighboring vacancy is found to be nearly twice that for motion of a free vacancy, the increased migration barrier presumably resulting from the absence of covalent interactions in the case of the sodium ion.

Impurity halide diffusion in silver chloride and silver bromide

Abstract Using the standard microtome-sectioning technique, the diffusion of bromide and iodide tracers in silver chloride and of chloride and iodide tracers in silver bromide has been studied. In silver chloride both bromide and iodide ions diffuse with the same activation energy as that of the chloride ion. In silver bromide the Arrhenius plots are curved: whereas the iodide ion has the same temperature-dependent activation energy as does bromide, the chloride ion appears to have a rather higher value at high temperatures, with all three energies approaching the same value at low tempeatures. These results are discussed in terms of vacancy mechanisms.

Low temperature suppression by chlorine of diffusion of gold in silver chloride

Abstract The tracer-sectioning technique was used to study the diffusion of aurous ion in silver chloride. Above 260°C, the diffusion proceeds interstitially with an activation energy of 0.47 eV. When the diffusion anneal was carried out in an external chlorine atmosphere, the diffusion coefficient was depressed. This behavior is explained in terms of the effect of chlorine on the cation vacancy concentration, and agrees quantitatively with results obtained from optical absorption studies by Ulrici, Koswig and Stasiw. Analysis of the data yields 0.62 eV for the heat of the reaction: ½Cl 2 = Cl − +cation vacancy + hole .

Effect of ionic polarizability on impurity-vacancy association in silver halides

Abstract Ionic conductivity measurements were used to determine the association enthalpies of divalent impurity ions and silver vacancies in silver chloride and silver bromide. The impurities were chosen, cognizant of previous work, to elucidate the effects of the ionic radius, the electronic structure, and host material. Conductance as a function of temperature was successfully measured for single crystals of AgCl doped with V 2+ , Cr 2+ , Fe 2+ , and Co 2+ , and on single crystals of AgBr doped with Mg 2+ , Ca 2+ , Sr 2+ , Ni 2+ and Cd 2+ . One main result from this investigation is the apparent independence of association enthalpies in AgCl from the size and electronic shell configuration of the first row transition metal ions. As expected, association enthalpy values were found to be smaller in AgBr than in AgCl. Also, a striking relationship between the ionic polarizability and the association enthalpy is demonstrated for AgBr.

Interactions of point defects with dislocations in silver chloride crystals

Abstract Internal friction techniques at 35 kHz were used to study the interactions between point defects and dislocations in crystals of silver chloride. The Granato-Lucke plots of the amplitude-dependent decrement were not linear, but were concave upward. Various analyses of these data all gave pin-dislocation binding energies of approximately 0·2 eV. An extensive study was made of the decay of the amplitude-independent decrement after “excitation” by high-amplitude oscillation; the Granato-Lucke L4 law was found valid, but the arrival of pins proceeded as t1/3, rather than the usual t2/3 found in deformed specimens. A first-order model of the response of a slightly perturbed Maxwell atmosphere about the dislocation is presented. The model quantitatively describes the experimental results. The activation energy of the rate constant was found to be 0·42 eV, consistent with data on solute diffusion and strain-aging.

Diffusion of strontium ion in silver chloride

Abstract The activation energy for diffusion of Sr 2 in AgCl has been found to be 0-98 eV, by means of a standard sectioning technique. The results are consistent with a vacancy mechanism and corroborate the hypothesis that ions with no outer d -shell electrons diffuse almost entirely substitutionally in silver halides.

Delineation of Tracks of Heavy Cosmic Rays and Nuclear Processes Within Large Crystals of Silver Chloride

Tracks of energetic charged particles, such as heavy primary cosmic rays and the products of nuclear collisions, have been made visible within the interior of large, transparent crystals of silver chloride. The tracks are delineated by photoelectric formation of metallic silver along them. This technique may be useful as a convenient and distortion‐free method for the study of heavy primaries and fission fragments.

Fast diffusion of cs+, a large alkali ion, in silver chloride☆

The diffusion of Cs+ tracer in AgCl has been measured in the temperature range 327–447°C. The unexpectedly small activation energy of 0.83 eV and tracer diffusivities larger than those of substitutional Ag+ have been interpreted in terms of local strain in the lattice, caused by the large radius of cesium, with a concomitant strong binding of a cation vacancy.