Grain alignment and critical current densities of (Bi,Pb)-2223 phase in the partial-melting and sintering process

Abstract

The grain alignment of the partially melted samples exists only in their surface layers. The Bi-2201 phase with the c-axis alignment, (Sr,Ca)CuO2 and (Sr,Ca)2CuO3 coexist in the surface layers of the air-cooled sample, whereas in the surface layers of the sample sintered at 840 °C for 18 h after being partially melted, the Bi-2212 phase with the c-axis alignment exists as a major phase. After prolonged sintering to 240 h, the c-axis-aligned Bi-2212 phase transforms to the c-axis-aligned Bi-2223 phase. The Bi-2201 phase in the air-cooled sample shows the sharpest and narrowest grain alignment, whereas the Bi-2223 phase in the sample sintered at 840 °C for 240 h exhibits the bluntest and widest alignment. Jc values of tapes which were heat treated by partial melting before wrapping with Ag sheets are larger than those of tapes without partial melting, and the tape which was sintered at 840 °C for 240 h after being partially melted at 875 °C prior to wrapping exhibits the highest Jc value. These results indicate that the partial-melting process is of real importance to the improvement of Jc in the (Bi,Pb)-2223 oxide superconductor.