Transmission electron microscopy for research of new layered oxides: studyof the Bi-Sr-Fe-O system

The Bi-Sr-Fe-O system has been revisited by transmission electron microscop y techniques. Three new layered oxides have been isolated and characterized . The first two oxides, Bi0.82Sr2.92FeO6-delta and Bi0.38Sr2.54Fe1.08O5-del ta, exhibit a 2201- and a 1201-type structure respectively, related to supe rconducting cuprates. Both oxides are characterized by mixed layers with a 1/1 ordering between Bi and Sr species. The transition from 2201 structure to 1201 structure occurs through a complex intergrowth mechanism and leads to an intermediate structure, formulated as Bi1.21Sr5.12FeO11-delta. It cor responds to a regular stacking between the; 1201 motif and the 2201 motif. These results are discussed in comparison with those previously obtained fo r the Bi-Sr-M-O systems (M = Cu, Mn or Co).