Applied Superconductivity Center, National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, USA.
Nat Mater. 2012 May 27;11(8):682-5. doi: 10.1038/nmat3333.
The K- and Co-doped BaFe(2)As(2) (Ba-122) superconducting compounds are potentially useful for applications because they have upper critical fields (H(c2)) of well over 50 T, H(c2) anisotropy γ < 2and thin-film critical current densities J(c) exceeding 1 MA cm(-2) (refs 1-4) at 4.2 K. However, thin-film bicrystals of Co-doped Ba-122 clearly exhibit weak link behaviour for [001] tilt misorientations of more than about 5°, suggesting that textured substrates would be needed for applications, as in the cuprates. Here we present a contrary and very much more positive result in which untextured polycrystalline (Ba(0.6)K(0.4))Fe(2)As(2) bulks and round wires with high grain boundary density have transport critical current densities well over 0.1 MA cm(-2) (self-field, 4.2 K), more than 10 times higher than that of any other round untextured ferropnictide wire and 4-5 times higher than the best textured flat wire. The enhanced grain connectivity is ascribed to their much improved phase purity and to the enhanced vortex stiffness of this low-anisotropy compound (γ1-2) when compared with YBa(2)Cu(3)O(7-x) (γ5).
K 和 Co 共掺杂的 BaFe(2)As(2)（Ba-122）超导化合物在应用中具有很大的潜力，因为它们的上临界场（H(c2)）超过 50T，H(c2)各向异性γ<2，薄膜临界电流密度 J(c)在 4.2K 时超过 1MA·cm(-2)（参考文献 1-4）。然而，Co 掺杂的 Ba-122 薄膜双晶在[001]倾斜取向超过约 5°时明显表现出弱连接行为，这表明需要纹理化的衬底才能应用，就像铜酸盐一样。在这里，我们呈现了一个相反的、更为积极的结果，其中无织构多晶（Ba(0.6)K(0.4))Fe(2)As(2)块状和圆形线材具有超过 0.1MA·cm(-2)（自场，4.2K）的传输临界电流密度，比任何其他无织构的亚铁砷化物线材都要高 10 倍以上，比最好的织构扁平线材高 4-5 倍。增强的晶粒连接性归因于它们大大提高的相纯度，以及与 YBa(2)Cu(3)O(7-x)（γ5）相比，这种低各向异性化合物（γ1-2）的磁通钉扎能力增强。
