Direct observation of nanometer-scale amorphous layers and oxide crystallites at grain boundaries in polycrystalline Sr1-xKxFe2As2 superconductors

摘要

We report here an atomic resolution study of the structure and composition ofthe grain boundaries in polycrystalline Sr0.6K0.4Fe2As2 superconductor. A largefraction of grain boundaries contain amorphous layers larger than the coherencelength, while some others contain nanometer-scale particles sandwiched inbetween amorphous layers. We also find that there is significant oxygenenrichment at the grain boundaries. Such results explain the relatively lowtransport critical current density (Jc) of polycrystalline samples with respectto that of bicrystal films.