Disordered commensurate structure of the 2212-related phase Fe{sub 2}(Bi{sub 0.69}Sr{sub 2.31})Fe{sub 2}O{sub 9.5+}/-{sub 1/2{delta}} and structural mechanism

Journal Article · Fri Dec 15 04:00:00 EST 2006 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1016/j.jssc.2006.08.015· OSTI ID:20900927

Grebille, Dominique ^[1]; Lepoittevin, Christophe ^[1]; Malo, Sylvie ^[1]; Perez, Oliver ^[1]; Nguyen, N ^[1]; Hervieu, Maryvonne ^[1]

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1. Laboratoire CRISMAT (UMR CNRS 6508), ENSICAEN, Bd du Marechal Juin, 14050 Caen Cedex (France)

The structure of the Fe{sub 2}(Bi{sub 0.69}Sr{sub 2.31})Fe{sub 2}O{sub 9.5-1/2{delta}} has been carried out by single crystal X-ray diffraction. Its structure can be considered as commensurately modulated with a basic structure of Fmmm symmetry and with a modulation vector q-bar ={alpha}a-bar {sup *}+{gamma}c-bar {sup *} whose {alpha} and {gamma} values are, respectively, equal to 1/3 and 1. The ferrite is described as a three-fold superstructure with a{approx}3a{sub p}2, b{approx}a{sub p}2 and c{approx}26A (space group Bbmb). It is described using a disorder model in agreement with diffuse scattering observations. The structure is built up from the intergrowth sequence between [(Bi, Sr)Fe{sub 2}O{sub 3.5+}/-{sub 1/2{delta}}]{sub {approx}} complex layers, related to the rock salt (RS)-type blocks, and double perovskite layers. Large analogies are found between the present structure and the so-called 2212 modulated structures related to the high T{sub c} superconductor copper oxides or to the corresponding Fe or Co oxides; they are discussed here. A statistical disorder characterizes the [Fe{sub 2}O{sub 2.5+}/-{sub 1/2{delta}}]{sub {approx}} double layer. Taking advantage of similar structural arrangements in related oxide compounds, a structural model is proposed. A description of this double layer is then given in terms of sequence of polyhedra (tetragonal pyramids, mono-caped tetrahedra and trigonal bi-pyramids), in comparison with other related modulated structures with different perioties. The powder sample exhibits a statistical distribution of {alpha} around an average value of 0.35; the oxygen non-stoichiometry appears as the driving force for the {alpha} value, i.e. for the modulation, commensurate or incommensurate. The Mossbauer study has been performed and interpreted on the basis of the refined structure.

• OSTI ID: 20900927
• Journal Information: Journal of Solid State Chemistry, Journal Name: Journal of Solid State Chemistry Journal Issue: 12 Vol. 179; ISSN 0022-4596; ISSN JSSCBI
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
BISMUTH COMPOUNDS
COPPER OXIDES
DIFFUSE SCATTERING
FERRITES
HIGH-TC SUPERCONDUCTORS
LAYERS
MONOCRYSTALS
ORTHORHOMBIC LATTICES
PEROVSKITE
SPACE GROUPS
STRONTIUM COMPOUNDS
STRUCTURAL MODELS
X-RAY DIFFRACTION