Bi12Sr22Fe11O56:: A new form of 2201/0201 "terraces" like structures, term m=6, n=11 of the [BiO2]m[Sr2FeO4]n family

A new oxide, namely Bi12Sr22Fe11O56, has been isolated in the Bi-Sr-Fe-O system. The transmission electronic microscopy studies carried out have permitted to characterise it as a double collapsed member derived from the regular intergrowth 2201/0201 type structure Bi2Sr4Fe2O10 (J. Solid State Chem. 118 (1995) 227). It crystallises in the space group I2/a with the following parameters: a = 38.82(1)angstrom, b = 5.731(2), c = 38.35(1)angstrom and beta = 121.31(2)degrees. Close relationships with the collapsed structure Bi13Ba2Sr25Fe13O66 (m = 7,n = 13) are shown. This new ferrite can be described as the (m = 6, n = 11) member of the [Bi2O2](m)[Sr2FeO4](n) family. The stairs are then 6 bismuth atoms wide and the K2NiF4 layers are 11 FeO6 octahedra thick. Moreover, the high-resolution electron microscopy images show the presence of local defects leading to the (m = 7, n = 11) member. Another description of this structure is also considered: it can be understood as slices of the parent structure, Bi2Sr4Fe2O10, separated by shearing zones. If the last ones seem to be the same in all the members, the thickness of the first ones can vary and so leading to different members of the new [Bi2Sr4Fe2O10](w) [Bi4Sr6Fe3O16] family. (c) 2005 Elsevier Inc. All rights reserved.