ELECTRON MICROSCOPY STUDY OF THE SUPERCONDUCTOR “Bi₂Sr₂CaCu₂O_8+δ”

Abstract

The structural study of the superconductor Bi 2 Sr 2 CaCu 2 O 8+δ was performed by X-ray diffraction on a single crystal, electron diffraction and electron microscopy. The structure of this oxide which crystallizes in the space group Amaa, with [Formula: see text] and c≃30.7 Å can be described as an intergrowth of an oxygen deficient double perovskite layer [Sr 2 CaCu 2 O 6 ] ∞ with ( BiO y ) 2 layers. The E.D. patterns show the existence of satellites in incommensurate positions. The HREM images and their simulation suggest that the [BiO y ] ∞ layers are not [ Bi 2 O 2 ] Aurivillius type layers. Modulations along the a axis and much more rarely along b are observed. Stacking defects are rarely observed along c: they correspond to the intergrowth of a phase Bi 2 Sr 2 CuO 6+δ which is assumed to be the superconductor at 22K previously detected for the nominal composition “ Bi 2 Sr 2 Cu 2 O 7 ”.