Effect of pre-annealing temperature and atmosphere on the microstructure and transport property of Bi-2223/Ag tapes

The phase assemblage and Bi-2212 texture in Bi-2223/Ag tapes before the heat treatment were varied by pre-annealing the tapes at different temperatures and in pure Ar or air for 10 h. Then all the tapes were isothermally heat treated at 840°C in air for 4 cycles with intermediate pressings. The J_c of the samples pre-annealed in pure Ar were lowered no matter which annealing temperature was used. The best J_c was obtained in the samples pre-annealed at 800°C in air, which was in an average value of 21.7 kA cm^-2, being increased by 25% compared with that of the unannealed tapes (17.3 kA cm^-2). The transport properties of various pre-annealed samples were correlated to the phase evolutions, growth and pre-alignment of Bi-2212 grains during pre-annealing.