SYNTHESIS AND PHASE-RELATIONS OF THE 110 K SUPERCONDUCTING 2223-PHASEIN THE BI-PB-SR-CA-CU-O SYSTEM

The influence of starting composition, especially the Bi:Pb ratio, on the formation of the 110 K superconducting 2223 phase was investigated . Compositional limits for 'pure' 2223 have been preliminarily determi ned in terms of Pb versus Bi + Pb. In samples with nominal composition Bi2+d-xPbxSr2Ca2Cu3Oz (d = 0), 2223 forms when x greater than or equa l to 0.2. The 2223 phase coexists with 2212 in the range 0.2 less than or equal to x less than or equal to 0.4 (i.e. with 10-20 mol% Si repl aced by Pb) after annealing at 855 degrees C for 100 h. Some (Ca,Sr)(2 )CuO3 is also found. The 2223 phase was the only superconducting phase in samples where x > 0.4; (Pb,Bi)(1.4)(Sr,Ca)(3)Cu0.77Oz was also fou nd in these samples. 'Pure' 2223 was obtained in samples with nominal composition Bi2+d-xPbxSr2Ca2Cu3Oz when x = 0.4 and d = 0.1, 0.2, 0.3. The 2223 phase can be formed from starting compositions with less than 10 mol% Bi replaced by Pb, provided (Bi + Pb) > 2. The 2201 phase coe xists with 2223 when (Bi + Pb) > 2.3 and Pb > 0.2.