Enhancement of critical current density of liquid-infiltration-processed YBaCuO bulk superconductors using milled Y _2BaCuO _5 powder

摘要

The size effects of a precursor Y _2BaCuO _5 (Y211) powder on the microstructure and critical current density (J _c) of liquid infiltration growth (LIG)-processed YBa _2Cu _3O _(7y) (Y123) bulk superconductors were investigated in terms of milling time (t). Y211 powders were attrition-milled for 010h in 2h increments at a fixed rotation speed of 400rpm. Y211 pre-forms were made by pelletizing the milled Y211 powders followed by subsequent sintering, after which an LIG process with top seeding was applied to the Y211/Ba _3Cu _5O _8 (Y035) pre-forms. Spherical pores were observed in all LIG-processed Y123 samples and the pore density gradually decreased as t increased from 0 to 8h. In addition to the reduced pore density, the Y211 particle size in the final Y123 products also decreased with increasing t. As t increased further to 10h, unexpected Y211 coarsening and large pore evolutions were observed. The magnetic susceptibilitytemperature curves showed that the onset superconducting transition temperature (T _(c,onset)) of all samples was the same (91.5K), but the transition width became greater as t increased. The J _c of the Y123 bulk superconductors fabricated in this study was observed to correlate well with t of the Y211 precursor powder. The maximum J _c of 1.0×10 ~5Acm ~2 (at 77K, 0T) was achieved at t=8h, which is attributed to the reduction in pore density and Y211 particle size. The prolonged milling time of t=10h decreased the J _c of the LIG-processed Y123 superconductor owing to the evolution of large pores and exaggerated Y211 growth.