A bismuth cobaltite with an intrinsically modulated misfit layer structure:: [Bi0.87SrO2]2[CoO2]1.82

A new misfit layer cobaltite [Bi0.87SrO2](2)[CoO2](1.82) has been synthesized. Its structure, solved from a single crystal X-ray investigation, shows CdI2 type [CoO2] layers similar to those encountered in misfit chalcogenides, but different rock salt (RS)-type [Bi0.87SrO2] layers. In contrast to the chalcogenides, these RS layers exhibit an intrinsic modulation due, as in the 2201 cobaltites, to the presence of double bismuth layers. Another fundamental difference with respect to misfit chalcogenides concerns the existence of strong Sr-O bonds between the [CoO2] layers and the [Bi0.87SrO2] layers, instead of weak bonds. (C) 1999 Academie des sciences/Editions scientifiques et medicales Elsevier SAS.