Improvement of J_c of Ag-Sheathed Bi-2212 Tapes Using Melt-Growth Technique under Reduced Oxygen Partial Pressure

Abstract

The growth behavior of Bi-2212 under the oxygen partial pressure of 0.01 atm has been investigated using Ag-sheathed tapes. In the partial melt state, a Cu-free phase and (Sr, Ca)CuO 2 have been observed as solid phases. The Cu-free phase has been assigned, tentatively, as Bi 2 Sr 2 CaO 6 . The grain size of the Cu-free phase has been found to depend critically on the starting composition. It decreases as the Sr content increases and the Ca content decreases, and accordingly, J c of the melt-processed tapes increases. The optimum composition is Bi 2 Sr 2.3 Ca 0.85 Cu 2 O z and the maximum J c is 1.5×10 5 A/cm 2 at 4 K.