Abstract
The chemical composition and the crystal structure of the Bi-Ca-Sr-Cu-O oxide with a high-Tc 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 Bi2Ca(x)Sr(z)Cu2O(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. (Author)