Relationship between Bi_2Sr_2CaCu_2O_x layer thickness and J_c enhancement by pre-annealing and intermediate rolling process

摘要

Pre-annealing and intermediate rolling (PAIR) process enables one to fabricate Bi_2Sr_2CaCu_2O_x (Bi-2212)/Ag tapes with high transport J_c > 5.0 * 10~5 A/cm~2 at 4.2 K, 10 T. We study the relationship between thickness of Bi-2212 layer and J_c enhancement by PAIR process for monolayer Bi-2212/Ag tapes. J_c enhancement by PAIR process is more significant for thinner Bi-2212 layer. For Bi-2212 layer less than 10 #mu#m thick, oxide J_c (4.2 K, 10 T) around 4.0 and 1.6 * 10~5 A/cm~2 are obtained for PAIR and no-PAIR samples, respectively, however, a large variation of J_c is seen for both series of samples in this thickness range. Good reproducibility of J_c is seen for the samples with the Bi-2212 layer around 20 #mu#m with oxide J_c (4.2 K, 10 T) around 3.2 * 10~5 A/cm~2. PAIR samples show smaller J_c variation than no-PAIR samples. J_c enhancement by PAIR process diminishes with increasing Bi-2212 layer thickness and disappears at the thickness around 50 #mu#M. PAIR process produces Bi-2212 layer with small variation of thickness (2-8% along the tape length and 2-19% across it), however, large variation of thickness (4-24% along the tape length and 30-80% across it) remains in no-PAIR samples. PAIR process has a large effect to improve the macroscopic homogeneity of Bi-2212 layer. This is supposed to be one of the reasons for the large J_c enhancement achieved by PAIR process.