Advantageous grain boundaries in iron pnictide superconductors

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 (theta(GB)) were systematically investigated for cobalt-doped BaFe2As2 (BaFe2As2:Co) epitaxial films fabricated on bicrystal substrates. The critical current density through bicrystal grain boundary (J(c)(BGB)) remained high (>1MA cm(-2)) and nearly constant up to a critical angle theta(c) of similar to 9 degrees, which is substantially larger than the theta(c) of similar to 5 degrees for YBa2Cu3O7-delta. Even at theta(GB) > theta(c), the decay of J(c)(BGB) was much slower than that of YBa2Cu3O7-delta.