Improvements of Superconducting Properties on Bi-2212 Bulks by Element Doping

Bi-2212 bulks have been fabricated by spark plasma sintering technique with the Bi-2212 precursor powders synthesized by co-precipitation process. The Al2O3 dopants were added into the precursor powders during the sintering process. The lattice parameters of Bi-2212 increased with Al content, suggesting that Al3+ ions entering into the lattice as interstitial ions due to the small ion radii. The carrier concentration has been calculated with measured room temperature thermopower values. The change of carrier concentration can be attributed to the changes of both Al and oxygen contents in the lattice. Therefore, by Al doping the samples have been tuned into optimal doping region with maximum critical temperature of 86K. The appearance of Al interstitial ions in the lattice caused certain amount of point defects, which acted as pinning centers. Therefore the flux pinning properties have been enhanced in the bulks, and obvious improvements of critical current density for over 55% have been obtained at 4.2K self-field.