Identification of a High-Tc Superconducting Phase in the Bi-Ca-Sr-Cu-O System

Abstract

Bismuth-based copper oxides with varying nominal compositions in the Bi-Ca-Sr-Cu-O system were prepared and identified by the methods of X-ray and electron diffraction, spectroscopic microanalysis and electrical resistivity measurement. It yielded a pseudo single phase with an offset superconducting transition temperature of 70 K and a width of 10 K. The major phase concerned with the superconducting transition near 75 K has a composition of Bi₂CaSr_1.5Cu₂O _y and is orthorhombic with unit cell dimensions of a=5.40, b=27.0 and c=30.6 Å. The X-ray diffraction pattern for the pseudo single phase was in good agreement with that simulated on the basis of proposed structure models which are fairly different from the structure of the layered bismuth titanate.