Advantageous grain boundaries in iron pnictide superconductors

TLDR

High‑Tc superconductors promise zero power loss for power lines, but grain‑boundary misalignment in polycrystals severely reduces critical current density. The study reports that iron‑pnictide superconductors exhibit superior grain‑boundary tolerance compared to cuprates. Transport across bicrystal grain‑boundary junctions with varying misorientation angles was systematically measured in cobalt‑doped BaFe₂As₂ epitaxial films grown on bicrystal substrates. The critical current density remained above 1 MA cm⁻² and nearly constant up to a misorientation angle of ~9°, larger than cuprates’ ~5°, and decayed more slowly beyond that, demonstrating pnictides’ greater grain‑boundary tolerance.

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. High critical temperature superconductors could be used to produce ideal electric power lines, but the misalignment of crystalline grain boundaries reduces current density. Here, pnictide superconductors are found to be more tolerant to misaligned grain boundaries than cuprates.