Improving the critical current density in Bi-2223 wires via a reduction of the secondary phase content

Progress in the performance of multifilamentary composite Bi-2223 wire fabricated at American Superconductor is reviewed. Critical current (I_c) performance of 175 A at 77 K and self-field and critical current density (J_c) performance of 22.1 kA/cm² (77 K, 0.1 T perpendicular to the tape plane) have been measured for short samples of Bi-2223 wire (standard size is 0.21×4.0×100 mm). Microstructure analysis by SQUID magnetometry, transmission XRD and TEM shows a large amount of residual 2212 intergrowth remaining in Bi-2223 grains. Residual 2212 intergrowth is seen to correlate with self-field J_c at 77 K across a range of experimental samples, suggesting that higher levels of performance will be achieved by further reducing residual 2212.