Interface effects on the current transport properties of multi-layered (Ba, K)Fe2As2 superconducting wires

Iron-based superconductors (IBSs) are very promising candidates for high-field applications owing to their ultrahigh upper critical field and very small electromagnetic anisotropy. For practical applications, it is essential to develop multifilamentary superconducting wires with high transport critical current density (J(c)). Here, we report the development of multi-layered Cu/Ag composite sheathed (Ba, K)Fe2As2 (Ba-122) superconducting wires using a tape-in-tube method. The wires consist of a tape-shaped Ba-122 filament with an improved grain alignment, showing an enhanced transport J(c) of 2.8 x 10(4) A cm(-2) at 4.2 K and 10 T, about two times higher than that of the Ba-122 wires prepared using the conventional powder-in-tube method. Furthermore, the evolution of the superconducting properties of the 3-, 7- and 11-filament tape-in-tube wires is systematically investigated in connection with the grain texture, mass redistribution and interface effects. Through 3D X-ray tomographic reconstruction and electron probe micro-analysis, we found that the filament uniformity and chemical composition homogeneity of the Ba-122 wires can be greatly affected by the interface between the Ba-122 filament and the Ag matrix. Our work suggested that in addition to the grain connectivity and grain texture that have been extensively studied for the single-core IBS wires, the Ba-122/Ag interface also plays an important role in the phase homogeneity and J(c) performance of the multifilamentary wires.