Superconductivity in the high-TcBi-Ca-Sr-Cu-O system: Phase identification

Abstract

Four phases are observed in superconducting Bi-Ca-Sr-Cu-O samples. The superconducting phase, with onset temperature near 120 K, is a 15.4-Å-layered compound with composition near ${\mathrm{Bi}}_2$ ${\mathrm{Ca}}_1$ ${\mathrm{Sr}}_2$ ${\mathrm{O}}_9$ and an A-centered orthorhombic unit subcell 5.41×5.44×30.78 A${̊}^3$. X-ray diffraction and electron microscopy data are consistent with a structure of alternating perovskite and ${\mathrm{Bi}}_2$ ${\mathrm{O}}_2$ layers. High-resolution transmission electron microscopy images reveal a b-axis superstructure of 27.2 Å, numerous (001) stacking faults, and other defects.