Improving superconducting properties of Bi-2212 tapes by Ca nonstoichiometry

Single filament tapes with different Ca contents Bi2.1Sr1.96Ca (x) Cu2.0O8+delta (x = 0.90, 0.95, 1.00, and 1.05) were prepared by powder in tube (PIT) process. The introduction of Ca nonstoichiometry caused systematic changes in the phase compositions of the final tapes, thus changing the chemical compositions of Bi-2212 phase. The increase of critical temperature T (c) from 81.2 to 84.2 K can be attributed to the carrier concentration change. The critical current density, J (c) and flux pinning properties were measured and evaluated at 4.2 K and high field (0-20 T) with the variation of Ca content. Obvious improvements of J (c) were obtained with the Ca content of x = 0.95 and 1.05 under perpendicular field, which implied that the chemical compositions changes of Ca could effectively lead to the formation of lattice defects, thus enhancing the flux pinning properties on the superconducting layers.