Effect of magnetic field strength in melt-processing on texture development and critical current density of Bi-oxide superconductors

Vertical magnetic fields up to 15 T were applied to the magnetic melt-processing (MMP) of Bi2212 bulks and Ag-sheathed tapes with a core thickness above 80 μm, which were set horizontally. Texture with the c-axis along the direction of magnetic field applied during MMP is developed due to the anisotropy in magnetic susceptibility of Bi2212. The degree of texture and the anisotropy factor in magnetization increase almost linearly as the magnetic field strength H_a during MMP is increased. The anisotropy factor in magnetization reaches 6.5 at a H_a of 13 T for Ag-doped Bi2212 bulks, whereas for Bi(Pb)2212 in which Pb partially substitutes for Bi the factor is suppressed to a half of that of Ag-doped Bi2212. The transport critical current I_c and the critical current density J_c of Bi2212 tapes also increase with increasing H_a due to the texture development and I_c reaches above 1000 A in self-filed for the tapes with a core thickness of 180 μm. However, for further thicker tapes, I_c decreases. The suppressions in the I_c for the tapes and in the anisotropy factor in magnetization for Bi(Pb)2212 bulks are due to inhomogeneous melting, and inhomogeneous nucleation and growth of crystals during MMP. When crystal growth is restricted, crystal alignment is suppressed.