Development of advanced MgB_2 superconducting tapes by controlling microstructure

本文通过对MgB_2粉末的细化，提高了MgB_2超导带材的临界电流密度（Jc）。这种改善归因于晶粒细化和碳替代。前者可能与附着在MgB_2颗粒上的MgO层的溶解有关。而后者则是由于残留的有机溶剂吸附在MgB_2的表面。晶粒细化增加了作为钉扎中心的晶界的面积。碳的替代增加了上临界场（Bc_2），从而成功地提高了带材的Jc值。经化学处理后，在4.2K和10 T下的Jc值达到4kA/cm^2。与使用未经处理的原始MgB 2粉末的带材相比，该值对应于十倍的增加。此外，这也适用于其他工艺，如球磨粉末，并进一步改善Jc可以预期。

We have improved critical current density (Jc) of MgB_2 superconducting tapes by the refinement of MgB_2 powder Ex-situ processed tapes using commercially available MgB_2 powders soaked in organic acid solutions show the improvement in transport Jc. This improvement is attributed to the grain pulverization and carbon substitution. The former is probably associated with the dissolution of MgO layers attaching to the MgB_2 grains. On the other hand, the latter originates from the remnant organic solvent adsorbing to the surface of MgB_2. The grain refinement increases the area of grain boundaries that acts as pinning centers. The carbon substitution increases upper critical field (Bc_2) Therefore, these effects successfully improve the Jc values of the tapes. The Jc values at 4.2 K and 10 T reach 4kA/cm^2 by the chemical treatment. This value corresponds to the tenfold increase, compared with the values of tapes using pristine MgB2 powders without treatment.This process is easy and low-cost which is suitable for the fabrication of long wires and tapes. Furthermore, this is applicable to other processes, such as ball-milled powders, and further improvement in Jc can expected.