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Author Linden, J. ♦ Karen, P. ♦ Kjekshus, A. ♦ Miettinen, J. ♦ Karppinen, M.
Source United States Department of Energy Office of Scientific and Technical Information
Content type Text
Language English
Subject Keyword MATERIALS SCIENCE ♦ CRYSTAL STRUCTURE ♦ GADOLINIUM OXIDES ♦ EUROPIUM OXIDES ♦ SAMARIUM OXIDES ♦ NEODYMIUM OXIDES ♦ BARIUM OXIDES ♦ IRON OXIDES ♦ STOICHIOMETRY ♦ SPECTROSCOPY ♦ ORDER PARAMETERS ♦ EXPERIMENTAL DATA
Abstract Single-phase samples of cubic REBa{sub 2}Fe{sub 3}O{sub 8+w} with RE = Gd, Eu, Sm, Nd were synthesized and equilibrated at 900 C in atmospheres with controlled partial pressures of oxygen. The oxygen content parameter w ranged from approximately {minus}0.30, which is the lower decomposition limit, to between w = 0.17 for RE = Gd and w = 0.37 for RE = Nd, achieved in O{sub 2} without crossing the upper limit. According to {sup 57}Fe Moessbauer spectroscopy, all samples are antiferromagnets at room temperature, with iron in high-spin states (S = 2 for Fe{sup 2+} and Fe{sup 4+}; S = 5/2 for Fe{sup 3+}). The contents of divalent or, alternatively, tetravalent iron states are consistent with the stoichiometry of the samples. At the stoichiometric composition (w = 0), all Moessbauer components correspond to trivalent iron, differing only in the coordination geometries of their oxygen neighborhoods. The sum-up of the observed coordination number shows that the oxygen disorder in these cubic (by X-ray diffraction) phases is a linear combination of the two limiting cases of oxygen vacancy distribution: binomial (random) and ordered (one vacancy per every third pseudocubic cell). This corresponds to a gradual change from the long-range order seen in triple-perovskite-type phases (RE = Er to Dy) via a short-range order seen in the present systems (RE = Gd to Nd) to a fully random disorder (RE = La). Eventual variations in w affect the coordination statistics in details, but change the overall picture very little.
ISSN 00224596
Educational Use Research
Learning Resource Type Article
Publisher Date 1999-05-01
Publisher Place United States
Journal Journal of Solid State Chemistry
Volume Number 144
Issue Number 2


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