Partial oxygen ordering in cubic perovskite REBa{sub 2}Fe{sub 3}O{sub 8+w} (RE = Gd, Eu, Sm, Nd)

Journal Article · Sat May 01 04:00:00 EDT 1999 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1006/jssc.1999.8178· OSTI ID:351519

Linden, J ^[1]; Karen, P; Kjekshus, A ^[2]; Miettinen, J; Karppinen, M ^[3]

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1. Aabo Akademi, Turku (Finland). Dept. of Physics
2. Univ. of Oslo (Norway). Dept. of Chemistry
3. Helsinki Univ. of Technology, Espoo (Finland)

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.

• OSTI ID: 351519
• Journal Information: Journal of Solid State Chemistry, Journal Name: Journal of Solid State Chemistry Journal Issue: 2 Vol. 144; ISSN 0022-4596; ISSN JSSCBI
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
BARIUM OXIDES
CRYSTAL STRUCTURE
EUROPIUM OXIDES
EXPERIMENTAL DATA
GADOLINIUM OXIDES
IRON OXIDES
NEODYMIUM OXIDES
ORDER PARAMETERS
SAMARIUM OXIDES
SPECTROSCOPY
STOICHIOMETRY