  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 (thetaGB) 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/cm2) and nearly constant up to a critical angle
thetac of ~9o, which is substantially larger than the thetac of ~5o for YBCO.
Even at thetaGB > thetac, the decay of JcBGB was much smaller than that of
YBCO.
