A Relative of Sr4Fe6O13 with Double Perovskite Layers: Bi4Sr14Fe24O56, m = 2-Members of a Potential Series [(Sr,Bi)2Fe4O7-(delta)][(Sr,Bi)2Fe2O6]m

A new ferrite Bi4Sr14Fe24O56 (i.e., Bi4/3Sr14/3Fe8O18.66) has been synthesized. The high-resolution electron microscopy study of this oxide shows that its modulated structure consists of an original intergrowth of double perovskite layers [(Sr,Bi)2Fe2O6] with oxygen-deficient [(Sr,Bi)2Fe4O7-(delta)] layers. The latter are closely related to the [Sr2Fe4O7-(delta)] layers observed in Sr4Fe6O13, that is, built up of FeO5 bipyramids and distorted tetragonal pyramids. This new oxide appears as the member m = 2 of a potential series [(Sr,Bi)2Fe4O7-(delta)] [(Sr,Bi)2Fe2O6]m, which offers a great possibility of cationic and oxygen nonstoichiometry, in connection with the structure modulation.