Superconducting transitions of BiSrCaCu2Ox quenched from high temperatures

The BiSrCaCu2Ox 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 specimen is essentially tetragonal. We found that the lower Tc as well as the higher Tc vary remarkably but differently as a function of a quenching temperature Tq. We present evidence that the opposite Tc variation observed between 400°C and 700°C cannot be attributed to a microscopic interaction between two phase but might be inherent.