FORMATION MECHANISM OF HIGH-T-C PHASE AND CRITICAL CURRENT IN (BI,PB)(2)SR2CA2CU3O10/AG TAPE

摘要

X-ray diffraction method was used to characterise the phase composition and investigate the formation mechanism of the (Bi,Pb)(2)Sr2Ca2Cu3O10 phase from the precursor with (Bi,Pb)(2)Sr2CaCu2O8 as the main phase. The reaction is found to be a two-dimensional nucleation (random)-growth type, -[ln(1-F)](1/2) = kt, where F is the conversional fraction of (Bi,Pb)(2)Sr2CaCu2O8 and t is the sintering time. The size of the critical current of the tape is quantitatively related to the conversional fraction of (Bi,Pb)(2)Sr2CaCu2O8 to (Bi,Pb)(2)Sr2Ca2Cu3O10 phase. At low fraction regime of (Bi,Pb)(2)Sr2CaCu2O10 the critical current of a tape shows no clear dependence on the remaining Bi-2212 phase, other factors such as grain alignment, colony size, contact between colonies, and fine nonsuperconducting particles become important in controlling the J(c). Also, in this regime, the predominant weak links seam to be the colony boundaries rather than the Bi-2212 phase. [References: 20]