Microstructure and transport properties of [0 0 1]-tilt bicrystal grain boundaries in iron pnictide superconductor, cobalt-doped BaFe2As2

Relationships between microstructure and transport properties of bicrystal grain boundary (BGB) junctions were studied in cobalt-doped BaFe2As2 (BaFe2As2:Co) epitaxial films grown on [0 0 1]-tilt bicrystal substrates of MgO and (La, Sr)(Al, Ta)O3 with misorientation angles θGB = 3–45°. The θGB of BaFe2As2:Co BGBs were exactly transferred from those of the bicrystal substrates. No segregation of impurities was detected at the BGB junction interfaces, and the chemical compositions of the BGBs were uniform and the same as those in the bulk film regions. A transition from a strongly-coupled GB behavior to a weak-link behavior was observed in current density–voltage characteristics under self-field around θGB ∼ 9°. The critical current density decreased from (1.2–1.6) × 106 A/cm2 of the intragrain transport to (0.7–1.1) × 105 A/cm2 of θGB = 45° because supercurrent becomes more governed by Josephson current with increasing θGB.