Effects of thermomechanical treatment on phase development and properties of Ag-sheathed Bi(Pb)-Sr-Ca-Cu-O superconducting tapes

The effects of thermomechanical treatment, starting composition, and Ag addition on microstructure and corresponding critical current density (J_c) of Ag sheathed Bi_1.8Pb_0.4Sr₂Ca_2.2Cu₃O_x (BSCCO) superconductor tapes made by a powder-in-tube technique have been studied. It was observed that for sintering in a 10% flowing oxygen atmosphere, 835-840 degrees C is the optimum processing temperature range for improved J_c. Above this temperature range, although the grain alignment increases, the content of 2223 phase decreases, resulting in a corresponding decrease in J_c. The tapes were subjected to repeated thermomechanical treatment of pressing and sintering. These thermomechanical treatments resulted in increased grain size and alignment, and increased content of 2223 phase, leading to increased J_c. X-ray analysis suggests that the 2212 phase reacts with non-superconducting phases, such as CaCuO₂, (SrCa)₂CuO₃, CaO, and CuO, to form the 2223 phase. Furthermore, addition of Ag to a superconducting BSCCO core slightly improved J_c without adversely affecting the transition temperature of a Ag-sheathed BSCCO tape.