Evidence for composition variations and impurity segregation at grain boundaries in high current-density polycrystalline K- and Co-doped BaFe{sub 2}As{sub 2} superconductors

Journal Article · Mon Oct 20 00:00:00 EDT 2014 · Applied Physics Letters

DOI:https://doi.org/10.1063/1.4898191· OSTI ID:22350967

Kim, Yoon-Jun ^[1]; Weiss, Jeremy D.; Hellstrom, Eric E.; Larbalestier, David C. ^[2]

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1. Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208 (United States)
2. Applied Superconductivity Center, National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310 (United States)

Some polycrystalline forms of the K- and Co-doped BaFe{sub 2}As{sub 2} and SrFe{sub 2}As{sub 2} superconductors now have a critical current density (J{sub c}) within a factor of ∼5 of that required for real applications, even though it is known that some grain boundaries (GBs) block current, thus, raising the question of whether this blocking is intrinsic or extrinsically limited by artefacts amenable to improvement by better processing. Herein, we utilize atom-probe tomography (APT) to study the grain and GB composition in high J{sub c} K- and Co-doped BaFe{sub 2}As{sub 2} polycrystals. We find that all GBs studied show significant compositional variations on the scale of a few coherence lengths (ξ), as well as strong segregation of oxygen impurities, which we believe are largely introduced in the starting materials. Importantly, these findings demonstrate that APT enables quantitative analysis of the highest J{sub c} K-doped BaFe{sub 2}As{sub 2} samples, where analytical transmission electron microscopy (TEM) fails because of the great reactivity of thin TEM samples. The observations of major chemical perturbations at GBs make us cautiously optimistic that there is a large extrinsic component to the GB current blocking, which will be ameliorated by better processing, for which APT will likely be a crucial instrument.

• OSTI ID: 22350967
• Journal Information: Applied Physics Letters, Vol. 105, Issue 16; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA); ISSN 0003-6951
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ARSENIC COMPOUNDS
BARIUM COMPOUNDS
CHANNELING
COBALT ADDITIONS
COHERENCE LENGTH
CRITICAL CURRENT
CURRENT DENSITY
DISTURBANCES
DOPED MATERIALS
GRAIN BOUNDARIES
IMPURITIES
IRON COMPOUNDS
PERTURBATION THEORY
POLYCRYSTALS
POTASSIUM ADDITIONS
SEGREGATION
STRONTIUM COMPOUNDS
SUPERCONDUCTORS
TERNARY ALLOY SYSTEMS
TRANSMISSION ELECTRON MICROSCOPY