Electron microscopy study of the superconductor ''Bi2Sr2CaCu2O8+δ''

The structural study of the superconductor Bi2Sr2CaCu2O8+δ was performed by X-ray diffraction on a single crystal, electron diffraction and electron microscopy. The structure of this oxide which crystallized in the space group Amaa, with α ≅ αrho√ 2,b ≅ arho √ 2 and c ≅ 30.7A can be described as an intergrowth of an oxygen deficient double perovskite layer -Sr2CaCu2O6∞ with (BiOy)2 layers. The E.D. patterns show the existence of satellites in incommensurate positions. The HREM images and their simulation suggest that the -BiOy∞ layers are not -Bi2O2 Aurivillius type layers. Modulations along the α axis and much more rarely along b are observed. Stacking defects are rarely observed along c: they correspond to the intergrowth of a phase Bi2Sr2CuO6+δ which is assumed to be the superconductor at 22K previously detected for the nominal composition ''Bi2Sr2Cu2O7''