Effect of doping on the superconductive properties of GdBa2Cu3O7−δ single-domain superconductors fabricated in air

The intrinsic effects of BaCuO2, Ga2O3 and nanoscopic Gd2BaCuO5 (Gd211) powders addition on the superconductive properties and microstructures of GdBa2Cu3O7−δ (Gd123) melt-solidified bulks fabricated in air have been investigated. The differential scanning calorimetry (DSC) measurements show that addition of Ga2O3 does not change the peritectic temperature of the mixtures. The microstructures of the Ga2O3-doped samples are similar to those observed in gallium-free samples. It is found that the magnetic critical current density (Jc) appears to be very sensitive to the change in carrier density near the optimal doping state. Interestingly, only when the impurity content and the oxygenation condition are both suitable then the evident secondary magnetization peak (SMP) appears. Finally, by proper oxygen control, a remarkable increase in the Jc at 2 T has been further induced due to an enhanced δTc pinning. As a result, the high-performance air-processed Gd123 single-domain samples without a post-annealing in Ar have been prepared. Further, this experiment suggests that carrier density and impurity concentration play a crucial role for SMP at 77.3 K.