Evolution of microstructure and superconducting properties originating from initial iron powders in (Ba, K)Fe 2 As 2 tapes

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Abstract
This paper investigates the effects of different iron powders on powder-in-tube (Ba, K)Fe ₂ As ₂ (Ba-122) superconducting tapes. The correlations between the particle size of iron powders and the microstructure, compositional homogeneity, and superconducting properties of the synthesized Ba-122 precursor and final tapes were systematically studied. The results show that the precursor prepared with μ m iron powder possesses fine grains and excellent chemical uniformity, which result in high phase purity and lower ferromagnetism that facilitating a high transport critical current density ( J c ) in tapes. In comparison, the tapes prepared with ∼30 μ m iron powder exhibits local compositional segregation and residual iron particles due to incomplete reactions. However, they contain larger Ba-122 grains which align more easily along the rolling direction, resulting in a significantly higher degree of c -axis texture. This enhanced texture effectively compensates for the adverse effects of reduced uniformity, enabling the 30 μ m sample to achieve a transport J c for tapes comparable to that of the μ m sample. In contrast, when iron powder with a particle size of ∼70 μ m is used, severe incomplete reactions lead to excessively large iron particles, which drastically lower material uniformity and density, thus significantly reducing the J c . These findings indicate that controlling the iron powder particle size within an appropriate range are crucial for achieving high J c in Ba-122 superconducting tapes.
Funding Information
  • National Natural Science Foundation of China (52377032)
  • International Partnership Program of the Chinese Academy of Sciences (116GJHZ2023005MI)
  • Natural Science Foundation of Shanghai (24ZR1423300)
  • The Beijing Municipal Science & Technology Commission, the Administrative Commission of Zhongguancun Science Park (Z251100003625029)

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