The La0.2Sr0.8Cu1-xFexO 3-δ perovskites are important because they are mixed electron and oxygen anion conductors and thus are able to serve as dense oxygen separation membranes. In order to better understand the mechanism for this separation a Mössbauer spectral study has been carried out to determine the ratio of iron(III) to iron(IV) in these mixed valent compounds. The Mössbauer spectra of La0.2Sr0.8Cu0.2Fe0.8O 3-δ obtained between 4.2 and 78 K reveal that its Néel temperature is ~75 K and the two well-resolved magnetic sextets observed between 4.2 and 45 K indicate the presence of trapped valence iron(III) and iron(IV). At 4.2 K the respective hyperfine fields are 454 and 299 kOe and the isomer shifts are 0.388 and 0.057 mm/s. The iron(III) to iron(IV) ratio is 1.20, a ratio which yields a δ value of 0.32 and, if one assumes the presence of only copper(II), a corresponding stoichiometry of La0.2Sr0.8Cu0.2Fe0.8O 2.68.
G. J. Long et al., "Magnetic and Mössbauer Spectral Study of Mixed Valent La0.2Sr0.8Cu0.2Fe0.8O2.68 and Related Perovskites," Journal of Applied Physics, vol. 85, no. 8 II B, pp. 5341-5343, American Institute of Physics (AIP), Apr 1999.
The definitive version is available at http://dx.doi.org/10.1063/1.370246
Materials Science and Engineering
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