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Point Defects and Cation Tracer Diffusion in (CrxFe1-x)3-δO4 Spinels

  • J. TÖpfer (a1) and R. Dieckmann (a1)

Abstract

The cation diffusion in the spinel solid solution (CrxFe1-x)3-δO4 (0 ≤ x ≤ 0.5) was experimentally investigated at 1200 °C as a function of oxygen activity, aO 2 (= PO 2/P°with P° = 1 bar) and cationic composition, x. Cation tracer diffusion coefficients, DMe' of Me = Co, Cr, Fe and Mn, were determined using the radioactiveisotopes Co-60, Cr-51, Fe-59 and Mn-54. For each cationic composition V-shaped log DMe vs. log aO 2 plots were obtained. The observed oxygen activity dependences indicate that the cation diffusion is determined by different point defect species prevailing at high and low oxygen activities, respectively. The observed oxygen activity dependences, in comparison with considerations based on point defect thermodynamics, suggest that cations diffuse via cation vacancies at high aO 2' while at low aO 2 cation interstitials prevail in the cation diffusion. In addition, new experimental data for tihe deviation from stoichiometry ≤in (CrxFe1-x)3-≤O4 are presented and discussed.

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[1] Dieckmann, R., Ber. Bunsenges. Phys. Chem. 86, 112 (1982).
[2] Dieckmann, R., Witt, C.A. and Mason, T.O., Ber. Bunsenges. Phys. Chem. 87, 495 (1983).
[3] Dieckmann, R., Mason, T.O., Hodge, J.D. and Schmalzried, H., Ber. Bunsenges. Phys. Chem. 82, 778 (1978).
[4] Birchenall, C.E., Oxidation of Metals and Alloys, ASM Monographs, Metals Park 1971, p. 193.
[5] Lu, F.H., Tinkler, S. and Dieckmann, R., Solid State lonics 62, 39 (1993).

Point Defects and Cation Tracer Diffusion in (CrxFe1-x)3-δO4 Spinels

  • J. TÖpfer (a1) and R. Dieckmann (a1)

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