Critical current density and microstructure of c-axis-oriented Bi 2Sr 2CaCu 2O χ and (Bi, Pb) 2Sr 2Ca 2Cu 3O χ superconducting tapes

Abstract

The critical current density J c is investigated as a function of both field direction and temperature in c-axis-oriented Bi 2Sr 2CaCu 2O χ “2212” and (Bi, Pb) 2Sr 2Ca 2Cu 3O χ “2223” polycrystals: a screen-printed “2212” tape with J c (77 K, 0 T) = 1.4×10 4 A/ cm 2, a screen-printed “2223” tape with J c (77 K, 0 T) = 1.5×10 4 A/ cm 2 and a Ag-sheathed “2223” tape with J c (77 K, 0 T) = 2.2×10 4 A/ cm 2. The J c versus θ data at 77 K with the angle θ between B and the c-axis show that J c in a field is influenced only by the field component parallel to the c-axis. There is a correlation between the anisotropy ratio γ=J c( B⊥ c)/J c( B|| c) and the half-height angular width Δθ of a peak for B ⊥ c . An increase of B in a sample enhances γ and narrows Δθ. At fixed B, the screen-printed “2212” tape has the largest γ and the narrowest Δθ in all samples, which corresponds to the SEM result showing the highest c-axis alignment. The second highest is the screen-printed “2223” tape and the lowest is the Ag-sheathed “2223” tape. J c in zero field increases almost linearly with decreasing temperature below 70 K, which is explained by the flux creep model.