Unified (3 + 1)-dimensional superspace description of the 2212-type stair-like [Bi₂Sr₃Fe₂O₉]_m[Bi₄Sr₆Fe₂O₁₆] family of compounds

Two commensurate members (m = 4, 5) of the 2212 stair-like family of compounds with the composition [Bi₂Sr₃Fe₂O₉]_m[Bi₄Sr₆Fe₂O₁₆] have been analyzed and refined in the (3 + 1)-dimensional superspace framework. Both compounds are described by a unique model, including displacive modulations. The assumption of the validity of the proposed model for a range of compositions allows a realistic prediction of the structures of other members of the family.