Flux Pinning Enhancement of Bi-2212 Tapes by Increasing Sr Content

Bi-2212 (Bi₂Sr₂CaCu₂O_8+x) multifilamentary round wires possess manifold superior superconducting properties compared to other high temperature superconductors suitable for very high field magnet applications; however, vortex pinning investigation has so far been absent, principally due to the complicated wire microstructures. Taking advantages of the simpler film-like microstructure of Bi-2212 tapes, we studied the flux pinning dependence as a function of Sr content, and correlated the tape performance to that of wires. We observed that, with increasing Sr content from 1.34 to 2.13, critical temperature T_c, and Kramer field H_k at 20 K increase respectively, from 70.5 to 80.4 K, and from 3.5 to 6.7 T, whereas α, which is the power law dependence of critical current density J_c at 4.2 K (J_c∝H^-α), decreases from 0.4 to 0.3. Our work shows that flux pinning in Bi-2212 wires can be further improved by optimizing the Sr content, and flux pinning on Bi-2212 tape is a versatile tool not only for wire pinning study but also for powder quality assurance.