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

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Abstract
The effects of thermomechanical treatment, starting composition, and Ag addition on microstructure and corresponding critical current density (Jc) of Ag sheathed Bi1.8Pb0.4Sr2Ca2.2Cu3Ox (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 Jc. Above this temperature range, although the grain alignment increases, the content of 2223 phase decreases, resulting in a corresponding decrease in Jc. 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 Jc. 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 Jc without adversely affecting the transition temperature of a Ag-sheathed BSCCO tape.