Crystalline Structures and Superconducting Properties of Rapidly Quenched BiSrCaCu2Ox Ceramics

Abstract

Phase changes and superconducting properties of rapidly quenched BiSrCaCu2Ox ceramics have been studied. The rapidly quenched sample consists of an amorphous state which begins to crystallize around 510°C. The crystal system was found to be tetragonal with a=5.39 Å and c=24.5 Å. By annealing above 700°C, a tetragonal system with a=5.41 Å and c=30.8 Å was produced. The former crystal was a semiconductor and the latter was a superconductor with Tc=75 K. A superconducting phase with Tc=105 K was observed in a sample annealed at 840°C. The superconducting volume ratio in the samples had a maximum at 803–840°C. The decrease of the volume ratio at the higher temperatures is considered to result from a decomposition of the superconducting phase (75 K) into a nonsuperconducting phase.