Achievement of practical level critical current densities in PIT Ba1-xKxFe2As2/Ag tapes by conventional cold mechanical deformation

We found that transport critical current density (Jc) of the Ba1-xKxFe2As2/Ag tapes is significantly enhanced by the combination process of cold flat rolling and uniaxial pressing. At 4.2 K, the Jc reaches a high value of 9.1x104 A/cm2 in 4 T, which is almost the practical level of 105 A/cm2. The Jc-H curve shows extremely small magnetic field dependence and keeps a high value of 6.9x104 A/cm2 in 10 T. These are the highest values reported so far for iron based superconducting wires. We also show our successful attempts of the fabrication of multi-filamentary tapes. A high Jc value of 5.3x104 A/cm2 (4.2 K, 10 T) was obtained in seven-filamentary tapes. The hardness and microstructure investigations reveal that the superior Jc in uniaxial pressed tape samples is due to the high core density, more textured grains and the change of microcrack structure. These results indicate that iron based superconductors are promising for high magnetic field applications.