Intergrain current flow in a randomly oriented polycrystalline SmFeAsO0.85 oxypnictide

TL;DR

This study investigates the intergrain current flow in polycrystalline SmFeAsO0.85, revealing limited current paths mainly affected by magnetic fields and emphasizing the importance of reducing grain boundary phases and cracks for improved superconductivity.

Contribution

It provides direct visualization and analysis of intergrain current paths in SmFeAsO0.85, highlighting the impact of Fe-As wetting phases and cracks on current connectivity.

Findings

Few grain-to-grain current paths observed

Magnetic fields switch off most current paths

Reducing Fe-As phase and cracks could improve current flow

Abstract

We report a direct current transport study of the local intergrain connections in a polycrystalline SmFeAsO0.85 (Sm1111) bulk, for which we earlier estimated significant intergranular critical current density Jc. Our combined low temperature laser scanning microscopy (LTLSM) and scanning electron microscopy observations revealed only few grain-to-grain transport current paths, most of which switched off when a magnetic field was applied. These regions typically occur where current crosses Fe-As, which is a normal-metal wetting-phase that surrounds Sm1111 grains, producing a dense array of superconducting-normal-superconducting contacts. Our study points out the need to reduce the amount of grain boundary-wetting Fe-As phase, as well as the crack density within pnictide grains, as these defects produce a multiply connected current-blocking network.