The influence of critical current density of Bi-2212 superconductors by defects after Yb-doping

• Ca substituting Yb element in Bi-2212 single crystal.
• The critical current density of this sample is the highest without the optimal Tc value.
• The Cu–O2 and Ca–O layers in pure and doping samples are observed using HRTEM.
• The optimal defect density is calculated.

Bi2Sr2Ca1−xYbxCu2O8+δ (Bi-2212) single crystals with x = 0.000, 0.005, 0.010 and 0.020 have been prepared by self-flux method. The influences of Yb doping on the formation of the dislocations in the lattice structures, as well as the related current carrying capability are investigated. Due to the SQUID measurement and the Bean model calculation, the maximum critical current density (Jc) is obtained when the Yb doping content is x = 0.010, though the Tc and the carrier concentration are not in the optimal region. Based on the HRTEM analyses of the Ca–O and Cu–O2 layers, the optimal dislocation density in the Cu–O2 layers is deduced according to the number of the dislocations per unit area. Besides, the sizes of the dislocations also prove the effectiveness of Yb substitution on the enhancement of the current carrying capability in Bi-2212 single crystals.