Grain Boundaries in Fe-Based Superconductors

Grain boundaries (GBs) as two-dimensional defects strongly influence and determine the current carrying capabilities of superconductors, may it be by providing efficient pinning centres or by constituting weak links. In this chapter, GB issues of polycrystalline bulks and wires as well as polycrystalline and bicrystal thin films of Fe-based superconductors are discussed for the most-studied, application-relevant systems: LnFeAs(O,F) (Ln: lanthanoid), P-, Co-, and Ni-containing AeFe2As2, (Ae: alkali earth), and Fe(Se,Te) in comparison to the cuprate high-Tc superconductors.