Fe 4+ formation in brownmillerite CaAl 0.5Fe 0.5O 2.5+ δ

• Published in: Materials letters Vol. 57; no. 28; pp. 4388 - 4393
• Main Authors: Waerenborgh, J.C., Rojas, D.P., Vyshatko, N.P., Shaula, A.L., Kharton, V.V., Marozau, I.P., Naumovich, E.N.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 2003
• Subjects: Brownmillerite; Calcium ferrite-aluminate; Crystal lattice; Mössbauer spectroscopy; Oxygen hyperstoichiometry; Thermogravimetry; Water absorption; Brownmillerite; Oxygen hyperstoichiometry; Calcium ferrite-aluminate; Mössbauer spectroscopy; Thermogravimetry; Crystal lattice; Water absorption
• ISSN: 0167-577X; 1873-4979
• DOI: 10.1016/S0167-577X(03)00330-6

A Mössbauer spectroscopy study of brownmillerite Ca 2FeAlO 5+ δ , in combination with the structure refinement from X-ray powder diffraction data, showed that hyperstoichiometric oxygen incorporation into the lattice is accompanied with Fe 4+ formation in the perovskite-like layers, which are built of oxygen–metal octahedra and preferably occupied by iron cations. This behavior differs from that of another layered ferrite, Sr 4Fe 6O 13+ δ , where the point defects formed due to oxidation are primarily accumulated in non-perovskite layers. The incorporation of even minor amounts of extra oxygen in Ca 2FeAlO 5+ δ leads to decreasing water absorption by the lattice, probably due to blocking of oxygen vacancies located in the tetrahedral layers of brownmillerite phase.