Structural Properties of Two Superconducting Phases in the Bi-Sr-Ca-Cu-O System

Abstract

X-ray powder diffraction patterns and transmission electron diffraction patterns of superconductors with the nominal composition of BiSrCa₃Cu₄O _x have been observed and compared with the results of the magnetic susceptibility. Unit cell dimensions of high-T _c phase (T _c∼107 K) are a=5.40 Å, b=27.0 Å, c=36.8 Å, indicating a pseudotetragonal symmetry. High resolution structure image of the high-T _c phase shows that there are layer structural units with 15.4 Å and 22.5 Å in thickness, in addition to the main layer structural unit with a thickness of 18.4 Å.