Structural characterization of a new vacancy ordered perovskite modification found for Ba3Fe3O7F (BaFeO2.333F0.333): Towards understanding of vacancy ordering for different perovskite-type ferrites

The new vacancy ordered perovskite-type compound Ba3Fe3O7F (BaFeO2.33F0.33) was prepared by topochemical low-temperature fluorination of Ba2Fe2O5 (BaFeO2.5) using stoichiometric amounts of polyvinylidene difluoride (PVDF). The vacancy order was found to be unique so far for perovskite compounds, and the connectivity pattern can be explained by the formula Ba-3(FeX6/2) (FeX5/2)(FeX3/2X1/1), with X= O/F. Mossbauer measurements were used to confirm the structural analysis and agree with the presence of Fe3+ in the above mentioned coordination environments. Group-subgroup relationships were used to build a starting model for the structure solution and to understand the relationship to the cubic perovskite structure. Furthermore, a comparison of a variety of vacancy-ordered iron-containing perovskite-type structures is given, highlighting the factors which favour one structure type over the other depending on the composition. (C) 2015 Elsevier Inc. All rights reserved