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Title: 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

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 likelymore » be a crucial instrument.« less
Authors:
 [1] ; ; ;  [2] ;  [1] ;  [3]
  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)
  3. (NUCAPT), Evanston, Illinois 60208 (United States)
Publication Date:
OSTI Identifier:
22350967
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Physics Letters; Journal Volume: 105; Journal Issue: 16; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
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