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The mobility of oxygen ions in CaF2

Akila, R and Jacob, KT (1990) The mobility of oxygen ions in CaF2. In: Journal of Applied Electrochemistry, 20 (2). pp. 294-300.

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The a.c. conductivity of CaF2 samples containing a fine dispersion of CaO particles has been measured in the temperature range 630 to 1100 K. The conductivity of the dispersed solid electrolyte is two orders of magnitude higher than that for pure polycrystalline CaF2 in the middle of the temperature range. Transport measurements on pure single crystals of CaF2 and polycrystalline samples, with and without CaO dispersion, using Fe+FeO and pure Fe as electrodes, clearly indicate that fluorine ions are the only migrating ionic species with a transport number of almost unity, contrary to the suggestion of Chou and Rapp [1, 2]. The enhanced conductivity of the dispersed solid electrolyte probably arises from two effects. A small solubility of oxygen in CaF2 results in an increase in the fluorine vacancy concentration and conductivity. Adsorption of fluorine ions on the surface of the dispersed particles of CaO results in a space charge region around each particle with enhanced conductivity. Measurements on a galvanic cell incorporating CaF2 as the solid electrolyte and oxide electrodes show that the e.m.f. is a function of the activity of CaO at the electrode/electrolyte interface. The response to an oxygen potential gradient is, therefore, through an exchange reaction, which establishes an equivalent fluorine potential at the electrode/electrolyte interface.

Item Type: Journal Article
Publication: Journal of Applied Electrochemistry
Publisher: Springer
Additional Information: Copyright of this article belongs to Springer.
Department/Centre: Division of Mechanical Sciences > Materials Engineering (formerly Metallurgy)
Date Deposited: 11 Jan 2011 07:17
Last Modified: 11 Jan 2011 07:17
URI: http://eprints.iisc.ac.in/id/eprint/34929

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