Utilization of neutron diffraction and Mِssbauer spectroscopy in the studies of the cathode for SOFCs

Neutron diffraction and Mössbauer spectroscopy were used to characterize the perovskite type cathodes, in terms of the crystal structure, oxygen occupancy, magnetic moment, and Fe valence state. It was found that a lower symmetry trigonal space group P-3C1 gave improved fits to the data including the matching of a peak not fitted in the R3¯c symmetry. A significant lattice distortion from rhombohedral to cubic was observed in La0.60Sr0.40FeO3−δ (L6SF) quenched from 1200 °C. Average Fe valence states are ∼3.04 and 3.36 for La0.60Sr0.40FeO3−δ quenched from 1500 and 700 °C, respectively. Results from neutron diffraction and Mössbauer spectroscopy indicated that [D.A. Berry, W.A. Surdoval, M.C. Williams, 222nd ACS National Meeting, Chicago, IL, United States, (2001)], in the specimen without quenching, there was no significant oxygen vacancy (δ=0), and ratio of Fe3+ over Fe4+ is 6/4, and [S.P. Simner, J.F. Bonnett, N.L. Canfield, K.D. Meinhardt, V.L. Sprenkle, J.W. Stevenson, Electrochem. Solid State Lett., 5, A173 (2002)] in the sample quenched from 1500 °C, δ was ∼0.2, and Fe exhibited a valence state of ∼3+.