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+1 Fe n O 3n+1 , single intergrowths with the generic formulation (A,Sr) n+2 Fe n O 3n+2 and (A,Sr) n+3 Fe n O 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 Sr 3 NdFe 3 O 9−δ , oxyhydroxydes hydrates and oxyhydroxydes such as Sr 3 NdFe 3 O 7.5 (OH) 2 ·H 2 O and Sr 3 NdFe 3 O 7.5 (OH) 2 can be created topotactically. Carbonate groups can also replace FeO 6 octahedra in the n = 3 member Sr 4 Fe 3 O 10 , leading to layered oxycarbonates Sr 4 Fe 3−x (CO 3 ) x O 10−4x with 0 < × ≤ 1. Shearing mechanism applied transversally to the layers allows collapsed structures to be generated such as the [Bi 2 Sr 3 Fe 2 O 9 ] n [Bi 4 Sr 6 Fe 2 O 16 ] family and the ferrite Bi 13 Ba 2 Sr 25 Fe 13 O 66 . Finally the replacement of rock salt SrO layers in the intergrowth Sr 2 FeO 4 allows a new series of modulated structures [Sr 8 Fe 12 O 26 ]·[Sr 3 Fe 2 O 6 ] n to be generated, built up of layers of FeO 5 bipyramids and tetragonal pyramids intergrown with perovskite layers.