Influence of CaCuO2 particle size on the phase evolution of Bi-based high temperature superconductors based on Two-powders Route

Abstract:

Bi_1.76Pb_0.34Sr_1.93Ca_2.0Cu_3.06O_8+d (Bi-2223) precursor powders were fabricated with a two-powder route based on co-precipitation process. During this process, Bi_1.76Pb_0.34Sr_1.93CaCu_2.06O_8+d (Bi, Pb-2212) and CaCuO₂ (with the actual phase composition of Ca₂CuO₃ and CuO) powders were first synthesized and calcinated separately, then mixed together before packed into Ag sheath. By tuning the pH values during the co-precipitation process, CaCuO₂ powders with different average particle size of ~1.10, 0.75, and 0.60 mm were obtained, respectively. Then single filament Bi-2223/Ag tapes were fabricated by powder in tube (PIT) process with precursor powders obtained by mixing the different particle sized CaCuO₂ powders and well-calcinated Bi-2212 powders. The influences of CaCuO₂ particle size on microstructure, phase evolution dynamics and superconducting current capacity of sintered Bi-2223 tapes were systematically studied. Due to higher uniformity of Ca₂CuO₃ and CuO distribution in filaments, clustering of secondary phases and insufficiently reacted areas were effectively avoided. Therefore, higher current capacity of ~12200 Acm^_-2 was obtained on the 1# tape by further optimizing the final dimension of the tapes.