Structure and Composition Analysis of High-T_c Superconducting Bi-Ca-Sr-Cu-O Oxide by High-Resolution Analytical Electron Microscopy

Abstract

The chemical composition and the crystal structure of the Bi-Ca-Sr-Cu-O oxide with a high- T c of about 75 K have been studied by the combined techniques of crystal structure imaging and spectroscopic microanalysis using a 400 kV high-resolution analytical electron microscope. The crystal is orthorhombic with lattice parameters a =0.54 nm, b =2.70 nm and c =3.06 nm. The chemical composition is assigned as Bi 2 Ca x Sr z Cu 2 O y , where x and z are approximately 1.0 and 1.5, respectively. The structure image reveals that the structure is comprised of a bismuth oxide layer interleaved with an oxygen deficient perovskite-like layer. It is suggested that a nearly commensurate superstructure based on the perovskite-type structure is formed.