A Large Family of Iron Ruddlesden‐Popper Relatives: from Oxides to Oxycarbonates and Oxyhydroxides

Iron oxides, oxyhydroxydes and oxycarbonates derived from the layered Ruddlesden‐Popper (RP) structure form a large family of layered compounds. Besides the classical RP oxides Sr_n+1Fe_nO_3n+1, single intergrowths with the generic formulation (A,Sr)_n+2Fe_nO_3n+2 and (A,Sr)_n+3Fe_nO_3n+3 (A = Tl, Pb, Bi…) can be generated by increasing the multiplicity of the rock salt layers, and multiple intergrowths of these single intergrowths can be synthesized. Starting from oxygen deficient RP oxides such as n = 3 member Sr₃NdFe₃O_9?δ, oxyhydroxydes hydrates and oxyhydroxydes such as Sr₃NdFe₃O_7.5(OH)₂·H₂O and Sr₃NdFe₃O_7.5(OH)₂ can be created topotactically. Carbonate groups can also replace FeO₆ octahedra in the n = 3 member Sr₄Fe₃O₁₀, leading to layered oxycarbonates Sr₄Fe_3?x(CO₃)_xO_10?4x with 0 < × ≤ 1. Shearing mechanism applied transversally to the layers allows collapsed structures to be generated such as the [Bi₂Sr₃Fe₂O₉]_n [Bi₄Sr₆Fe₂O₁₆] family and the ferrite Bi₁₃Ba₂Sr₂₅Fe₁₃O₆₆. Finally the replacement of rock salt SrO layers in the intergrowth Sr₂FeO₄ allows a new series of modulated structures [Sr₈Fe₁₂O₂₆]·[Sr₃Fe₂O₆]_n to be generated, built up of layers of FeO₅ bipyramids and tetragonal pyramids intergrown with perovskite layers.