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 $J_{\mathrm{c}}$ 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 $J_{\mathrm{c}}$ for ${\theta }_{\mathrm{GB}}\le 9^{\circ }$, indicative of strong coupling between the grains.

arXiv comment6 figures, with Supplementary Information

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• Status of Iron Based Superconductors: characteristics and relevant properties for applications