Microstructure and superconducting properties of Bi2-xPbxSr2CaCu2Oy spherical particles transformed from an amorphous state prepared by a containerless melt solidification method

We successfully prepared amorphous Bi-Pb-Sr-Ca-Cu-O (Bi:Pb:Sr:Ca:Cu:O=2-x:x:2:1:2:y) spherical particles by a containerless melt solidification method. These particles were obtained by the melt solidification of Bi2-xPbxSr2CaCu2Oy ((Bi,Pb)-2212) powder during the free-fall using a propane gas torch. The diameter of these particles was about 100 mu m. The crystalline (Bi,Pb)-2212 superconductors were obtained by the transformation from the amorphous state under several oxygen partial pressures (P-O2=0.01, 0.21 and 1 atm). (Bi,Pb)-2212 phase was formed via (Bi,Pb)(2)Sr2CuOy phase for all P-O2 values. Low P-O2 was more effective to introduce Pb into Bi2Sr2CaCu2Oy, lattice and only the heat treatment under P-O2=0.01 atm was successful in obtaining Pb-rich (Bi,Pb)-2212 with modulation-free structure. The critical composition separating Pb-poor modulated and Pb-rich modulation-free structures in (Bi,Pb)-2212 was x approximate to 0.5. However, no lamellar structure composed of modulated and modulation-free regions was present in any particles for all P-O2 values. Enhancement of critical current density was obtained by the Pb substitution.