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Title:Effect of pressure on ionic conductivity in rubidium silver iodide and silver iodide
Author(s):Allen, Paul Clement
Doctoral Committee Chair(s):Lazarus, David
Department / Program:Physics
Subject(s):ionic conductivity
rubidium silver iodide
silver iodide
single crystals
Abstract:The effect of pressure on the ionic conductivity of RbAg4I5 and AgI has been measured, using single crystals and polycrystalline samples, up to pressures of 6 kbar. The activation volumes for motion in cr-RbAg4I5 and B-RbAgI5, respectively, are -0.4 ±.2 cm3/mole and -0.2 ±.l cm3/mole. In 4a-AgI, the motion volume increases from 0.56 ±.l cm3 /mole at 435 K to 0.8 ±.l cm3/mole at 623 K. These values are unusually small in relation to the activation energies and are not consistent with the strain energy model or a domain diffusion mechanism. The negative activation volume for super-ionic RbAgIand the small size of the activation volume for cr-AgI may be 4S the result of pressure increasing the interaction enthalpy between the diffusing ions. The logarithms of the ionic conductivities of cr-and B-RbAgIin4S crease linearly at first and then decrease quadratically with pressure. This is related to the large quadratic pressure dependence of the second-order transition temperature, 6T (K) = 0.14lP (kbar) + 0.111p2 (kbar2). c The variation of the 122 K transition temperature with pressure is 6T(K) = S.6SP (kbar) -0.S3P2 (kbar2), implying a molar volume change of c VB -Vy = 0.37 ±.Ol cm3 /mole and a change in compressibility KB -Ky = 0.033 ±.OOI x 10-11 cm2/dyne, across the transition. The ionic conductivity of y-RbAg Iinitially decreases with an 4S activation volume of 9 ±l cm3/mole, and then levels off with increasing pressure. This may be the result of an extrinsic-like region or of grain-boundary conduction. The negative activation volume for conduction along the c-axis in B-AgI has been confirmed. Both low-temperature phases have large formation volumes consistent with the theory of Rice et al. of transitions to the superionic phase.
Issue Date:1977
Genre:Dissertation / Thesis
Rights Information:1977 Paul Clement Allen
Date Available in IDEALS:2011-07-01
Identifier in Online Catalog:252664

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