Superior transport current densities in (Ba, K)Fe2As2 superconducting tapes realized by combined strengthening of grain texture and flux pinning

Iron-based superconductors, characterized by a high upper critical field and small anisotropy, have been regarded as prospective candidate material for high magnetic field applications. For such applications, it is essential to develop iron-based superconducting wires and tapes with high in-field critical current density (Jc). In view of material microstructure, large-sized superconducting grains with high-degree of grain texture are preferable for high efficiency current transportation, but on the other hand will sacrifice some grain boundaries that act as potential flux pinning centers. Here, based on powder-in-tube method, a novel approach combining medium temperature pressing and hot isostatic pressing was developed for the fabrication of Cu/Ag composite sheathed (Ba, K)Fe2As2 (Ba-122) iron-based superconducting tapes. Microstructural analysis reveals lager grain size and improved grain texture produced by the combined processes, and at the same time, high-density nano-size dislocations were induced in grains, which further enhanced the current carrying ability at high field region. As a result, high transport Jc of 1.6×105A /cm2 at 4.2K and 10T was obtained for the Ba-122 tapes, and more importantly, due to the significantly reduced field dependence of Jc, the transport Jc was still kept above the practical level of 105A /cm2 at high fields up to 25T. At 25T, the value of Jc exceeds 60% of its value at 10T, indicating a minimal reduction in iron-based superconducting wires and tapes. This study demonstrates a favorable microstructure that will help to approach superior current transport performance under high magnetic fields for iron-based superconductors.