Superconducting Transitions of BiSrCaCu2Ox Quenched from High Temperatures

Abstract

The BiSrCaCu₂O _x specimens have been quenched from various elevated temperatures (200°C ∼860°C) to liquid nitrogen. The X-ray diffraction study revealed that the crystalline structure of specimens is essentially tetragonal. We found that the lower T _c as well as the higher T _c vary remarkably but differently as a function of a quenching temperature T _q. We present evidence that the opposite T _c variation observed between 400°C and 700°C cannot be attributed to a microscopic interaction between two phases but might be inherent.