Stacking faults and superstructures in a layered brownmillerite




Kruger, Hannes
Stöber, S
Welberry, Thomas
Withers, Raymond
Fitz Gerald, John

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Munksgaard International Publishers


Single crystals of Ca 4Fe 2Mn 0.5Ti 0.5O 9 have been synthesized using a flux method. The structural characterization using single-crystal X-ray diffraction revealed the space group Amma and unit-cell dimensions of a = 5.3510 (6), b = 26.669 (3), c = 5.4914 (6) Å. The structure is isotypic with Sr 3NdFe 3O 9 [Barrier et al. (2005). Chem. Mater. 17, 6619-6623] and exhibits separated brownmillerite-type layers. One-dimensional diffuse scattering shows that the unit cell is doubled along c by alternating the intra-layer order of tetrahedral chains, causing stacking faults along the b direction. A computer simulation was performed, proving that the observed intensity variations along the diffuse scattering rods originates from two different local structures depending on the configuration of the tetrahedral chains. Selected-area electron diffraction experiments exhibit well ordered regions characterized by satellite reflections corresponding to two different superstructures. Both superstructures can be described using the superspace group A21/m(0βγ)0s, with γ = 0.5 and β ≃ 0.27 or β = 0.



Keywords: Brownmillerites; Diffuse scattering; Flux methods; Intensity variations; Intra-layer; Local structure; modulated structure; Satellite reflections; Selected area electron diffraction; Single crystal x-ray diffraction; Space Groups; Structural characterizat diffuse scattering; layered brownmillerite; modulated structure; stacking faults



Acta Crystallographica Section B: Structural Science


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