The effect of K-na co-doping on the formation and particle size of Bi-2212 phase

Superconducting K-Na co-doped Bi2Sr2KxCa1Cu1.75Na0.25Oy (x=0, 0.05, 0.1 and 0.25) ceramics are prepared by a solid-state reaction method. It is clearly determined from XRD data that the characteristic peaks of Bi-2212 phase are observed in all samples. The resistivity measurements show that Tc (onset) values is gradually increasing as K content is increased. It is also found that K-Na co-doping influence the grain sizes for Bi-2212 phase significantly. The critical current densities as a function of magnetic field have been calculated from M–H hysteresis loops of samples according to Bean's critical model, indicating that K-Na co-doping cause higher Jc values than the pure ones.