Open AccessStacking faults and superstructures in a layered brownmillerite
Author(s) -
Krüger H.,
Stöber S.,
Welberry T. R.,
Withers R. L.,
Fitz Gerald J. D.
Publication year - 2011
Publication title -
acta crystallographica section b
Language(s) - English
Resource type - Journals
eISSN - 1600-5740
pISSN - 0108-7681
DOI - 10.1107/s0108768111042005
Subject(s) - brownmillerite , stacking , materials science , geology , crystallography , chemistry , physics , nuclear magnetic resonance , perovskite (structure)
Single crystals of Ca 4 Fe 2 Mn 0.5 Ti 0.5 O 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 3 NdFe 3 O 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 A 2 1 / m (0βγ)0 s , with γ = 0.5 and β≃ 0.27 or β = 0.