Effects of Bi and Bi/sub 2/0/sub 3/ additions on the microstructure and superconducting properties of powder-in-tube BSCCO (2212) tapes

摘要

The microstructural development and superconducting properties of Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub x/ (Bi-2212) Ag-clad powder-in-tube tapes with 2 vol% bismuth (Bi) added from either Bi (s) or Bi/sub 2/O/sub 3/ powders were investigated. Such additives reduce the peritectic decomposition temperature of pure Bi-2212 by approximately 15-20/spl deg/C. Scanning electron microscopy (SEM) and optical microscopy on polished top and cross-sections revealed that the volume fraction of Bi-free phases was lower in the Bi-added specimens relative to those based on pure Bi-2212. In addition, it appeared that the Bi-added samples had improved grain alignment, which was confirmed by X-ray diffraction analysis. Magnetic hysteresis (at 5 K between /spl plusmn/5.5 T) and transport measurements (at 4.2 K) were performed on each specimen. These results showed that Bi-additions yielded superior magnetization critical currents, which is attributed to improved grain alignment and reduced secondary phases.