Connectivity and flux pinning improvements in Ag-clad BSCCO-2223 tapes produced by changes in the cooling rate

The rate at which Ag-clad (Bi, Pb)_2Sr_2Ca_2Cu_3O_ x tapes are cooled from their final reaction heat treatment influences both the intergranular connectivity and intragranular flux pinning strength of the polycrystalline filaments. As the cooling rate from 825 °C to 730 °C in 7.5% O_2 was decreased over a range of 5 °C/min to 0.005 °C/min, J _ c (77 K, 0 T) increased from ∼8 to ∼24 kA/cm^2, and the irreversibility field increased from, ∼120 to, ∼200 mT. The J _ c (4.2 K, 0 T) increased in a similar fashion. Cooling slowly also sharpened the critical temperature transition and increased the critical onset temperature from 107 K to 109 K. These improvements in the superconducting properties occurred despite partial decomposition of the (Bi, Pb)_2Sr_2Ca_2Cu_3O_ x phase into non-superconducting impurity phases during the slow cooling. A microstructural basis for these multiple effects is described.