Effect of oxygen on superconductivity and structure of Bi-system superconductor

A systematic study of the effects of oxygen content and distribution in 2223 single-phase Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O_10+δ s superconductor has has been carried out using a combination of quenching in air and low-temperature annealing in nitrogen. With decreasing oxygen content a maximum was observed in T_c, accompanying the increase in room-temperature resistivity. Also the effect of oxygen redistribution has been studied by low-temperature annealing in nitrogen, which allows no oxygen content change. After this annealing, in T_c, the room temperature resistivity and the c-axis parameter an apparent change occurred as compared to the original quenching states. From tge measurement of in situ resistivity which increased gradually during low-temperature annealing, it seems that a metastable phase was formed by oxygen diffusion. The interchange of oxygen atoms between Bi₂O₂ and CuO₂ planes and the possible ordering of oxygen vacancies were proposed to explain the relevant experimental phenomena.