Formation mechanism of high- Tc and critical current in (Bi,Pb) 2Sr 2Ca 2Cu 3O 10/Ag tape

Abstract

X-ray diffraction method was used to characterise the phase composition and investigate the formation mechanism of the (Bi,Pb) 2Sr 2Ca 2Cu 3O 10 phase from the precursor with (Bi,Pb) 2Sr 2CaCu 2O 8 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) 2Sr 2CaCu 2O 8 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) 2Sr 2CaCu 2O 8 to (Bi,Pb) 2Sr 2Ca 2Cu 3O 10 phase. At low fraction regime of (Bi,Pb) 2Sr 2CaCu 2O 8, 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 to be the colony boundaries rather than the Bi-2212 phase.