INFLUENCE OF OXYGEN CONTENT ON SUPERCONDUCTIVITY OF Bi-SYSTEM MATERIAL

The sample with nominal composition Bi_1.8Pb_0.35Sr₂Ca₂Cu₃O_y was prepared by solid state reaction method. Through the measurements of resistivity, dc. susceptibility, and the analysis of X-ray diffraction and Energy Dispersive X-ray (EDX) microanalysis, we found that: (1) there is only one superconducting transition with transition temperature near 110K, its zero-resistance temperature (Tce) is as high as 106.5K, the diffraction pattern is similar to that of 2223 single phase (110K), but the cation ratio of Bi:Pb:Sr:Ca:Cu is near 25.8:5.74:18.43:19.53:30.50, i.e., Bi_2.5Pb_0.5Sr₂Ca₂Cu₃.We suppose that the 3223 phase is caused by intergrowth in the sample; (2) like the 1-2-3 phase material, the superconductivity of Bi-system is sensitive to oxygen content. We suppose that different oxygen content in the same crystal structure leads to the change of electronic structure, and so to great difference in the superconductivity.