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 1.8 Pb 0.4 Sr 2 Ca 2.2 Cu 3 O 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 CaCuO 2 , (SrCa) 2 CuO 3 , 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.