Microstructure and critical current densities of Bi-2223 superconductor solidified in high magnetic fields

The microstructure and critical current densities of Bi-2223 superconductor with Ag₂O and MgO additions after partial-melting and solidification in high magnetic fields were investigated. It has been found that the Bi-2212 grains with their c-axis parallel to the magnetic field are formed after partial-melting and solidification in 8 T magnetic field, and transform into the Bi-2223 grains with c-axis alignment during the further sintering process at 1113 K in zero magnetic field. The optimum partial-melting temperatures T_max of non-added, 5 mass%Ag₂O and 5 mass%MgO added samples are 1147 K, 1143 K and 1153 K, respectively. 5 mass%Ag₂O and 5 mass%MgO additions enhance the c-axis alignment of (Bi, Pb)-2223 phase. The largest J_c value appears in the 5 mass%MgO added sample with T_max=1153 K. MgO particles homogeneously disperse in the oriented (Bi, Pb)-2223 platelets. The MgO added sample has small non-superconducting second phase particles, whereas the Ag₂O added sample has large second phase particles.