Effect of temperature and atmosphere on stability of high-T c phases in Bi–Pb–Sr–Ca–Cu–O superconductors

The effect of temperature and atmosphere on stability of the high-Tc phase in Bi1.8Pb0.4Sr2Ca2Cu3Ox superconductors has been investigated using ac susceptibility, x-ray diffraction, and Raman measurements. It is found that the high-Tc phase becomes unstable due to the structural phase transformation at temperature above 650 °C in O2 of 1 atm. The formation and the decomposition of the high-Tc phase is found to occur through the medium of the Ca2PbOx phase and depends on oxygen partial pressure at temperature above 650 °C.