Microstructural evolution mechanism of Ba0.6KαFe2As2 Cu/Ag composite sheathed superconducting tapes

Low-cost Cu/Ag composite sheathed Ba${}_{\mathrm{0.6}}$K${}_{\alpha }$Fe₂As₂ superconducting tapes have been the focus of considerable research interest in terms of superconducting properties and performance improvement. The K-doping content has a great influence on the transport critical current density ($J_c$) of Cu/Ag composite sheathed tapes. This study analyzes the evolution occurring within the micro-composition and the mechanism affecting the transport $J_c$ in Ba${}_{\mathrm{0.6}}$K${}_{\alpha }$Fe₂As₂ (0.42 $\le$ $\alpha$ $\le$ 0.54) raw material, by modulating the ratio of K. It has been demonstrated that both extremes of K content, namely an insufficient or excessive amount, have an adverse effect on phase purity of the powders. Consequently, this has a direct impact on the transport $J_c$ of tapes. Cu/Ag tapes fabricated using a precursor powder with an optimal K ratio $\alpha \sim$0.464 exhibited the highest performance, with a $J_c$ of 5.8 × 10⁴ A cm ⁻² at 10 T and 4.2 K. The optimized Cu/Ag composite tapes have been found to have superior advantages for high-field applications.