Improving phase transformation and superconducting performance of Bi-2223 tapes via Cu addition

Chemical composition plays a significant role in high-performance Bi₂Sr₂Ca₂Cu₃O_10+δ high-temperature superconductors (Bi-2223 HTS). Particularly, the Cu element can influence phase transformation, thus the superconducting performance in the Bi-2223 system. The precursor powders with different x wt.% Cu addition content (x = 0, 1, 2, and 3) were fabricated using the spray pyrolysis (SP) method. Bi-2223 single-filamentary tapes were fabricated by the powder-in-tube process (PIT) using precursor powders with different Cu addition content. The influences of Cu addition content on the phase formation, microstructural, and superconducting performance of Bi-2223 tapes have been investigated. With the increase of Cu addition content, Bi-2223 phase formation activation energy decreases from 16293.6 to 8173.2 kJ/mol. This indicates that the addition of Cu can promote the formation of Bi-2223 phase. The highest Bi-2223 phase content is obtained with 1% Cu addition. The improved inter-grain connection could be attributed to both higher phase content and larger grain size. Therefore, the maximum critical current (I_c) of 50 A at 77 K was achieved. On the other hand, the T_c^onset can be improved to 112 K in 2% Cu addition. The change of T_c^onset can be attributed to the formation of a nearly tetragonal lattice with proper composition. The results may also be applicable to the fabrication of multi-filamentary Bi-2223/Ag tapes with higher current capacity.