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Title:Studies of thermal and transport properties of the isostructural family of rubidium silver iodide
Author(s):Vargas, Ruben Antonio
Doctoral Committee Chair(s):Salamon, Myron B.
Department / Program:Physics
Subject(s):thermal properties
transport properties
isostructural family
rubidium silver iodide
mobile ion subsystem
ionic conductor
Abstract:A detailed experimental study has been made of the effect of ordering of the mobile ion subsystem of an ionic conductor on its ionic conductivity near the second order phase transition for each ·of the member of the isostructural family MAg4Is (M = Rb, NH4 , K). The specific heat Cp and the temperature derivative of the resistivity dR/dT of these compounds were measured simultaneously as a function of temperature using the ac method. The differential aspects of the resistivity measurements and the high resolution of the temperature modulation method permitted the first detailed study of the properties associated with the critical phenomena of these systems. These measurements were made on single crystals grown from solution. Diffused silver contacts were used as electrodes, considerably minimizing contact effects. It was found that Cp and dR/dT exhibit very similar critical behavior near the corresponding critical points for each of the compounds, i.e., Tc = 208'.8°K, 198.7°K and 194.lo K, for M = Rb, NH 4 , K, respectively. It was established that an accurate linear proportionality between the logarithmic derivative of the conductivity d(lnsigma)/dT and Cp over several decades of reduced temperature above and below Tc is a property of these systems. The specific heat data for (NH4)A9I and KAg4I show a power law divergence, with Ising-like critical exponents, as is the case for RbAg4I5 whose transition has been studied extensively. Sufficient evidence has been accumulated to identify such a transition as an order-disorder one. A model of diffusion that treats local order beyond the usual mean-field theory approaches has been found to account for the observed critical behavior of the ionic mobility and, through the constant of proportionality, gives microscopic information about the way occupational short-range order affects the ionic mobility. The dependence of the experimental pararneters--defined in terms of the models to which the data is fitted--on the monovalent cation M+ is discussed and possible assignments are suggested.
Issue Date:1977
Genre:Dissertation / Thesis
Rights Information:1977 Ruben Antonio Vargas
Date Available in IDEALS:2011-07-01
Identifier in Online Catalog:252919

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