Advertisement

Journal of Applied Electrochemistry

, Volume 20, Issue 2, pp 294–300 | Cite as

The mobility of oxygen ions in CaF2

  • R. Akila
  • K. T. Jacob
Article

Abstract

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.

Keywords

Fluorine CaF2 Solid Electrolyte Polycrystalline Sample Potential Gradient 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. [1]
    R. W. Ure Jr,J. Chem. Phys. 26 (1957) 1363.Google Scholar
  2. [2]
    W. Bollmann and H. Henniger,Phys. Stat. Sol. (a) 11 (1973) 367.Google Scholar
  3. [3]
    Idem, ibid. 16 (1973) 187.Google Scholar
  4. [4]
    L. E. Nagel and M. O'Keefe, in ‘Fast Ion Transport in Solids’ (edited by W. Van Gool), North Holland, Amsterdan (1973) p. 165.Google Scholar
  5. [5]
    J. M. Reau and J. Portier, in ‘Solid Electrolytes’ (edited by P. Hagenmuller and W. Van Gool), Academic Press, New York (1978) p. 313.Google Scholar
  6. [6]
    T. L. Markin, in ‘E.m.f. Measurements in High Temperature Systems’ (edited by C. B. Alcock), The Institution of Mining and Metallurgy, London (1968) p. 91.Google Scholar
  7. [7]
    T. N. Rezukhina and T. F. Sisoeva,J. Chem. Thermody. 11 (1979) 1095.Google Scholar
  8. [8]
    S. F. Chou and R. A. Rapp, in ‘High Temperature Metal Halide Chemistry’ (edited by D. L. Hildenbrand and D. D. Cubicciotti), The Electrochemical Society, N.J. (1978) p. 392.Google Scholar
  9. [9]
    Idem, J. Electrochem. Soc. 130 (1983) 506.Google Scholar
  10. [10]
    T. A. Ramanarayanan, M. L. Narula and W. L. Worrell,ibid. 126 (1979) 1360.Google Scholar
  11. [11]
    K. T. Jacob, D. B. Rao and H. G. Nelson,ibid. 125 (1978) 758.Google Scholar
  12. [12]
    V. Levitskii, A. Hammou, M. Dulcot and C. Deportes,J. Chim. Phys. 73 (1976) 305.Google Scholar
  13. [13]
    S. Fujitsu, M. Miyayama, K. Koumoto, H. Yanagida and T. Kanazawa,J. Mater. Sci. 20 (1985) 2103.Google Scholar
  14. [14]
    A. Khandkar, V. B. Tare and J. B. Wagner Jr,Rev. Chim. Minerale 23 (1986) 274.Google Scholar
  15. [15]
    N. Vaidehi, R. Akila, A. K. Shukla and K. T. Jacob,Mater. Res. Bull. 21 (1986) 909.Google Scholar
  16. [16]
    J. Maier,J. Phys. Chem. Solids 46 (1985) 309.Google Scholar
  17. [17]
    J. Maier,Mater. Res. Bull. 20 (1985) 383.Google Scholar
  18. [18]
    D. R. Stull et al., ‘JANAF Thermochemical Tables’, 2nd edn, NSRDS-NBS 37, US Dept. of Commerce, Washington D.C. (1971).Google Scholar
  19. [19]
    B. C. H. Steele, in ‘Electromotive Force Measurements in High Temperature Systems’ (edited by C. B. Alcock), The Institution of Mining and Metallurgy, London (1968) p. 3.Google Scholar
  20. [20]
    K. T. Jacob, G. M. Kale, R. Akila and A. K. Shukla,High Temp. Mater. Processes 7 (1986) 141.Google Scholar
  21. [21]
    E. M. Levin and H. F. McMurdie, ‘Phase Diagrams for Ceramists’, Supplements, Am. Ceram. Soc. (1969) and (1975).Google Scholar
  22. [22]
    R. Benz and C. Wagner,J. Phys. Chem. 65 (1961) 1308.Google Scholar

Copyright information

© Chapman and Hall Ltd. 1990

Authors and Affiliations

  • R. Akila
    • 1
  • K. T. Jacob
    • 1
  1. 1.Department of MetallurgyIndian Institute of ScienceBangaloreIndia

Personalised recommendations