Fe4+ formation in brownmillerite CaAl0.5Fe0.5O2.5+delta

resumo

A Mossbauer spectroscopy study of brownmillerite Ca2FeAlO5 + delta, in combination with the structure refinement from X-ray powder diffraction data, showed that hyperstoichiometric oxygen incorporation into the lattice is accompanied with Fe4+ 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, Sr4Fe6O13 + delta, 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 Ca2FeAlO5 + delta leads to decreasing water absorption by the lattice, probably due to blocking of oxygen vacancies located in the tetrahedral layers of brownmillerite phase. (C) 2003 Elsevier Science B.V. All rights reserved.

palavras-chave

MOSSBAUER-SPECTROSCOPY; HIGH-TEMPERATURE; TRANSPORT-PROPERTIES; THERMAL-EXPANSION; PEROVSKITES; CA2FEALO5; CONDUCTIVITY; VACANCIES

categoria

Materials Science; Physics

autores

Waerenborgh, JC; Rojas, DP; Vyshatko, NP; Shaula, AL; Kharton, VV; Marozau, IP; Naumovich, EN

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