Chemically degraded grain boundaries in fine-grain Ba<sub>0.6</sub>K<sub>0.4</sub>Fe<sub>2</sub>As<sub>2</sub> polycrystalline bulks
Fumitake Kametani, Yi-Feng Su, Yesusa Collantes, Chongin Pak, C. Tarantini, D. C. Larbalestier, E. E. Hellstrom
Abstract
In this study, we investigated nanostructure and local compositional variations at grain boundaries (GBs) in polycrystalline Ba0.6K0.4Fe2As2 (K-Ba122) bulks. Analytical scanning transmission electron microscopy revealed that K-Ba122 bulks made in a regular glove box filled with 99.9% Ar show Ba–O segregation at the GBs, forming a network of insulated GBs. By significantly reducing the oxygen and water content in the glove box, K became preferential segregation at GBs. Our nanostructural study suggests that the K-Ba122 GBs are easily compromised by different kinds of chemistry variations that can be fully addressed only by synthesis in a very clean environment.