The Influence of Precursor Powder on Critical Current Density of Ag/Bi-2223 Tapes

摘要

The influence of the precursor powders on critical current density (Jc) of Ag/Bi-2223 tapes has been investigated. The phase assemblages of the precursor are controlled by calcinating conditions. The precursor powders and tapes were characterized by XRD and SEM. Jc value of Bi/Ag-2223 tapes strongly depends on the precursor powder. (Bi,Pb)2223 phase formation and the connections between grains are determined by amount of (Bi,Pb)2212, Ca_2PbO_4, Ca_2CuO_3 and CuO in the precursor. A better phase assemblage of the precursor is obtained at 845 deg C for 12h. Extending the calcination time and raising the calcination temperature result in the decrease of the relative amount of Ca_2PbO_4 and CuO, but in an increase of the amount of 2212 phase and Ca_2CuO_3. When the temperature is raised up to 860 deg C, the peak of the 2223 phase appears and the peak of Ca_2PbO_4 disappears in the X-ray duffraction spectrum. The Jc value of the final tapes is reduced as the precursor powder contains some 2223 phases. A suitable amount of Ca_2PbO_4 is helpful to heal microcracks, then Jc value of the tapes is improved.