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.

• Received 2 February 1988

DOI:https://doi.org/10.1103/PhysRevLett.60.1174

This article appears in the following collection:

Heating up of Superconductors

This collection marks the 30th anniversary of the discovery of high-temperature superconductors. The papers selected highlight some of the advances that have been made to date, both in understanding why these compounds behave in the way they do, and in utilizing them in applications.