Structural analysis and transport properties of [010]-tilt grain boundaries in Fe(Se,Te)

Understanding the nature of grain boundaries is a prerequisite for fabricating high-performance superconducting bulks and wires. For iron-based superconductors [e.g. Ba(Fe,Co)2As2, Fe(Se,Te), and NdFeAs(O,F)], the dependence of the critical current density Jc on misorientation angle (θGB) has been explored on [001]-tilt grain boundaries, but no data for other types of orientations have been reported. Here, we report on the structural and transport properties of Fe(Se,Te) grown on CeO2-buffered symmetric [010]-tilt roof-type SrTiO3 bicrystal substrates by pulsed laser deposition. X-ray diffraction and transmission electron microscopy revealed that θGB of Fe(Se,Te) was smaller whereas θGB of CeO2 was larger than that of the substrate. The difference in θGB between the CeO2 buffer layer and the substrate is getting larger with increasing θGB. For θGB≥24∘ of the substrates, θGB of Fe(Se,Te) was zero, whereas θGB of CeO2 was continuously increasing. The inclined growth of CeO2 can be explained by the geometrical coherency model. The c-axis growth of Fe(Se,Te) for θGB≥24∘ of the substrates is due to the domain matching epitaxy on (221) planes of CeO2. Electrical transport measurements confirmed no reduction of inter-grain Jc for θGB≤9∘, indicative of strong coupling between the grains.