# Grain boundary characteristics of oxypnictide NdFeAs(O,F) superconductors

## TL;DR

This study investigates the intrinsic grain boundary effects in NdFeAs(O,F) superconductors, revealing a critical angle of 8.5°, similar to other Fe-based superconductors, by minimizing extrinsic damage effects.

## Contribution

It provides the first systematic analysis of intrinsic grain boundary characteristics in NdFeAs(O,F) superconductors, clarifying the critical angle for weak-link behavior.

## Key findings

- Critical grain boundary angle of 8.5° identified
- Weak-link behavior caused by extrinsic damage in previous studies
- Intrinsic properties similar to other Fe-based superconductors

## Abstract

We have systematically investigated the grain boundary (GB) angle dependence of transport properties for NdFeAs(O,F) fabricated on [001]-tilt symmetric MgO bicrystal substrates. In our previous study, NdFeAs(O,F) bicrystal films showed a weak-link behaviour even at a GB angle of 6{\deg}. However, this was caused by an extrinsic effect originating from the damage to both NdFeAs(O,F) and MgO substrate by excess F-diffusion along the grain boundary. To investigate the intrinsic nature of grain boundaries, we minimized the damage to NdFeAs(O,F) and MgO by reducing the deposition temperature of NdOF over-layer needed for F-doping. The resultant NdFeAs(O,F) bicrystal films have a critical angle of 8.5{\deg}, above which Jc starts to decrease exponentially. This critical angle is almost the same as those of other Fe-based superconductors.