A new 2212-type stair like structure:: Bi14Sr21Fe12O61, m=5 member of the generic [Bi2Sr3Fe2O9]m[Bi4Sr6Fe2O16] family

A new oxide. Bi14Sr21Fe12O61, with a layered structure derived from the 2212 modulated type structure Bi2Sr3Fe2O9, was isolated. It crystallizes in the 12 space group, with the following parameters: a = 16.58(3) Angstrom, b = 5.496(1) Angstrom, c = 35.27(2) Angstrom and beta = 90.62degrees. The single crystal X-ray structure determination, coupled with electron microscopy, shows that this ferrite is the m = 5 member of the [Bi2Sr3Fe2O9](m)[Bi4Sr6Fe2O16] collapsed family. This new collapsed structure can be described as slices of 2212 structure of five bismuth polyhedra thick along a(-->), shifted with respect to each other and interconnected by means of [Bi4Sr6Fe2O16] slices. The latter are the place of numerous defects like iron or strontium for bismuth substitution; they can be correlated to intergrowth defects with other members of the family. (C) 2004 Elsevier Inc. All rights reserved.