2-STEP DEPENDENCE OF CRITICAL-TEMPERATURE ON OXYGEN-CONTENT FOR THE BI-PB-SR-CA-CU-O SUPERCONDUCTOR

Single phase Bi1.8Pb0.33Sr1.99Ca1.86Cu3O(y) superconducting powder was prepared by a solid-state reaction. The weight loss (DELTA-w) due to the oxygen desorption was investigated in Ar gas by thermogravimetric analysis, and the critical temperature (T(c)) was measured for the powder which was quenched from 500-degrees-C-830-degrees-C to room temperature in Ar gas. For the powder quenched from 500-degrees-C, the T(c) was 107 K. The value of T(c) decreased to 98 K when DELTA-w reached 0.41 wt.%. In this DELTA-w range, \dT(c)/d-DELTA-w\ decreased with increasing DELTA-w. In the DELTA-w range of 0.41 wt.%-0.53 wt.%, the T(c) remarkably decreased from 98 K to 88 K with increasing DELTA-w. In the DELTA-w range of 0.53 wt.%-0.73 wt.%, the T(c) was almost constant. That is, the double step behavior was observed in the T(c) versus oxygen content curve for the 110 K phase. The oxygen sites for variable stoichiometry were discussed on the basis of the results of thermal analyses and the change in lattice parameters in addition to this.