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

Abstract

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) $2$ As $2$ , Fe(Se,Te), and NdFeAs(O,F)], the dependence of the critical current density $Jc$ on misorientation angle ( $\theta \mathrm{GB}$ ) 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 CeO $2$ -buffered symmetric [010]-tilt roof-type SrTiO $3$ bicrystal substrates by pulsed laser deposition. X-ray diffraction and transmission electron microscopy revealed that $\theta \mathrm{GB}$ of Fe(Se,Te) was smaller whereas $\theta \mathrm{GB}$ of CeO $2$ was larger than that of the substrate. The difference in $\theta \mathrm{GB}$ between the CeO $2$ buffer layer and the substrate is getting larger with increasing $\theta \mathrm{GB}$ . For $\theta \mathrm{GB}\ge 24\circ$ of the substrates, $\theta \mathrm{GB}$ of Fe(Se,Te) was zero, whereas $\theta \mathrm{GB}$ of CeO $2$ was continuously increasing. The inclined growth of CeO $2$ can be explained by the geometrical coherency model. The $c$ -axis growth of Fe(Se,Te) for $\theta \mathrm{GB}\ge 24\circ$ of the substrates is due to the domain matching epitaxy on (221) planes of CeO $2$ . Electrical transport measurements confirmed no reduction of inter-grain $Jc$ for $\theta \mathrm{GB}\le 9\circ$ , indicative of strong coupling between the grains.

Keywords: Fe(Se,Te); domain matching epitaxy; roof-type grain boundary.