Advantageous grain boundaries in iron pnictide superconductors

Abstract

High critical temperature superconductors have zero power consumption and could be used to produce ideal electric power lines. The principal obstacle in fabricating superconducting wires and tapes is grain boundaries—the misalignment of crystalline orientations at grain boundaries, which is unavoidable for polycrystals, largely deteriorates critical current density. Here we report that high critical temperature iron pnictide superconductors have advantages over cuprates with respect to these grain boundary issues. The transport properties through well-defined bicrystal grain boundary junctions with various misorientation angles (θGB) were systematically investigated for cobalt-doped BaFe2As2 (BaFe2As2:Co) epitaxial films fabricated on bicrystal substrates. The critical current density through bicrystal grain boundary (JcBGB) remained high (>1 MA cm−2) and nearly constant up to a critical angle θc of ∼9°, which is substantially larger than the θc of ∼5° for YBa2Cu3O7–δ. Even at θGB>θc, the decay of JcBGB was much slower than that of YBa2Cu3O7–δ.

Anomalous scaling behavior in a mixed-state Hall effect of a cobalt-doped BaFe2As2epitaxial film with a high critical current density over 1 MA/cmSato1, Katase2, Kang3 et al. 2013Phys. Rev. BSelf Cite17170View full textAdd to dashboardCite

“…[9] Compared to cuprates, the properties of iron-pnictide Josephson-junction devices remain inferior due largely to their metallic characters. However, their superior grain boundary properties [10] along with high upper critical magnetic fields (H c2 ) ≥ 50 T and small anisotropic factors γ = H c2 //ab / H c2 //c = 1-2 [11] are promising for wire [12][13][14] and tape applications. [15,16] Similar to cuprates, the extrinsic pinning centers largely control J c in iron pnictides.…”

High transport critical current densities in textured Fe-sheathed Sr1−xKxFe2As2+Sn superconducting tapes

“…The early results indicate that the global critical current is limited by intergrain currents over the grain boundaries in polycrystalline bulk and wires [12][13][14][15][16][17][18]. Recent experiments revealed that high-angle grain boundary largely deteriorates critical current density J c in Ba(Fe 1-x Co x ) 2 As 2 bicrystals [19,20]. These results suggest that the discovered iron based superconductors are exhibiting weak link grain boundary behavior similar to high-T c cuprate superconductors.…”

Huge critical current density and tailored superconducting anisotropy in SmFeAsO0.8F0.15 by low-density columnar-defect incorporation

“…T he reasonably high values of the superconducting transition temperature T c , very high upper critical magnetic fields and generally low anisotropy of the recently discovered iron-based superconductors [1][2][3] enable operation in economically interesting temperature-field ranges and, at the same time, minimize detrimental effects due to grain boundaries and thermal fluctuations 4,5 . However, the overriding application metric, the maximum loss-less electrical current density, is ultimately determined by the vortex pinning that can be engineered into the material.…”