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Incommensurate Nuclear and Magnetic Structure of the Oxygen-Deficient Perovskites (Ba2−3xBi3x−1)(Fe2xBi1−2x)O2+3/2x (0.43≤x≤0.50)

✍ Scribed by Ph. Boullay; D. Grebille; M. Hervieu; B. Raveau; E. Suard

Publisher
Elsevier Science
Year
1999
Tongue
English
Weight
520 KB
Volume
147
Category
Article
ISSN
0022-4596

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✦ Synopsis

The actual nuclear and magnetic structures of the oxygen perovskites [Ba 2؊3x Bi 3x؊1 ][Fe 2x Bi 1؊2x ]O 2؉3x/2 (0.40 < x40.50) were studied combining XRPD and NPD data. The incommensurate modulated structures of the members x ‫؍‬ 0.45 and x ‫؍‬ 0.48 were determined in the superspace formalism. It is shown that bismuth and barium cations are not distributed at random over a single site but exhibit a particular ordering which can be described by a substitutional modulation. In such structures, the displacement of the cation from its average position is much larger for bismuth than for barium. The modulated fourfold superstructure of Bi 2 Ba 2 Fe 4 O 11 (x ‫؍‬ 0.50), 99a p ؋ a p ؋ 4a p :: is closely related to those of incommensurate phases, with a 99Bi 1/4 Ba 3/4 Ba 1/4 :: ordering of the cations. Nevertheless, a certain disordering of these cations and oxygen vacancies are evidenced in the superstructure. The antiferromagnetic (AF) ordering is the same for all the members: iron spins are antiferromagnetically coupled along [110] and along [001] forming (001) AF planes.

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