Redox behaviour of Sr4Fe6O13 +/-delta by Mossbauer spectroscopy and neutron diffraction

abstract

Mossbauer spectroscopy studies of the intergrowth Sr4Fe6O13 +/- delta phase, in combination with the structure refinement from X-ray and neutron powder diffraction data, showed that the point defects formed due to oxygen nonstoichiometry variations from approximately - 0.45 up to + 0.14 are accumulated in the nonperovskite layers, built of oxygen-iron polyhedra with pentacoordinated Fe cations. These defects include oxygen vacancies and Fe2+ cations, or oxygen interstitials and Fe4+ in the case of oxygen deficiency or hyperstoichiometry, respectively. The oxidation state of iron cations and the occupancy of oxygen sites in the perovskite-like layers, built of O2--Fe3+ octahedra in the Sr4Fe6O13 (+/-) (delta) lattice, are both essentially independent of the oxygen stoichiometry variations. The perovskite layers act thus as a frame of the lattice, which provides a substantial stability and a moderate chemically induced expansion on the oxygen content variations, but leads to relatively low ionic and electronic conductivities. (C) 2003 Elsevier Science B.V. All rights reserved.

keywords

OXYGEN PERMEATION PROPERTIES; POWDER DIFFRACTION; PHASE; PEROVSKITES; VACANCIES; TRANSPORT; SYSTEM; SR

subject category

Materials Science; Physics

authors

Waerenborgh, JC; Avdeev, M; Patrakeev, MV; Kharton, VV; Frade, JR

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