Fabrication conditions and superconducting properties of Ag‐sheathed Bi‐Sr‐Ca‐Cu‐O tapes prepared by partial melting and slow cooling process

Ag‐sheathed Bi2Sr2Ca1Cu2Ox(Bi‐2212) tapes with various oxide superconductor core (SC‐core) thicknesses, SC‐core ratios (SC‐core area to overall cross‐sectional area), and tape configurations were prepared by a partial melting and slow cooling process. For single‐core tapes the critical current density, Jc(core), for SC‐core, increases with decreasing SC‐core thickness, due to the highly aligned Bi‐2212 grains, and the highest Jc(core) of 1.4×105 A/cm2 at 4.2 K in 10 T is achieved at a core thickness of 15 μm. Furthermore, the Jc(core) increases with increasing SC‐core ratio (i.e., with decreasing Ag‐sheath thickness). From the practical point of view, high Jc(overall) as well as high critical current (Ic) is more important than Jc(core). This requirement is attained by the double‐tube method, which shows the highest Jc(overall) value of 3.0×104 A/cm2 at 4.2 K in 10 T. In the tape fabrication process, the slow heating rate just below the partial melting becomes important, because oxygen released from the S...