A-site deficiency, phase purity and crystal structure in lanthanum strontium ferrite powders

• Published in: Solid state ionics 2007-07, Vol.178 (21), p.1326-1336
• Main Authors: Striker, T., Ruud, J.A., Gao, Y., Heward, W.J., Steinbruchel, C.
• Format: Article
• Language: English
• Subjects: A-site stoichiometry; LSF; Perovskite; Phase analysis; SOFC cathode
• ISSN: 0167-2738; 1872-7689
• DOI: 10.1016/j.ssi.2007.06.011

Lanthanum strontium ferrite (LSF) powders of average composition of (La 1− x′ Sr x′ ) y′ FeO 3+ δ , were fabricated over a range of average strontium composition between 0.2 ≤ x′ ≤ 0.5 and average A-site occupancy between 0.8 ≤ y′ ≤ 1.0. Samples that were originally determined to be perovskite phase pure using X-ray diffraction with CuK α radiation were found to have significant amounts of non-perovskite phases when evaluated using high-energy synchrotron radiation. As-fabricated samples with nominal A-site deficiency, y′ < 1, contained a hexaferrite phase. When treated at 955 °C in pO 2 = 10 − 10  atm, those samples contained magnetite. The actual composition of the perovskite phase was corrected to account for the presence of the second phases through mass balance calculations. As a result, the actual A-site deficiency of the perovskite phase was much lower than the average value of the bulk powder. For as-fabricated powders with x′ < 0.4, it was determined that the A-site deficient LSF perovskite phases were metastable. At equilibrium, a mixture of A-site stoichiometric perovskite and hexaferrite phases was present. The refined perovskite crystal structures and unit cell volumes were consistent with literature trends.