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Title: On the Nanoscale Structure of K xFe 2-yCh 2 (Ch = S, Se): A Neutron Pair Distribution Function View

Comparative exploration of the nanometer-scale atomic structure of K xFe 2-yCh 2 (Ch = S, Se) was performed using neutron total scattering-based atomic pair distribution function (PDF) analysis of 5 K powder diffraction data in relation to physical properties. Whereas K xFe 2-ySe 2 is a superconductor with a transition temperature of about 32 K, the isostructural sulphide analogue is not, which instead displays a spin glass semiconducting behavior at low temperatures. The PDF analysis explores phase separated and disordered structural models as candidate descriptors of the low temperature data. For both materials, the nanoscale structure is well described by the iron (Fe)-vacancy-disordered K 2Fe 5-yCh 5 (I4/m) model containing excess Fe. An equally good description of the data is achieved by using a phase separated model comprised of I4/m vacancy-ordered and I4/mmm components. The I4/mmm component appears as a minority phase in the structure of both K xFe 2-ySe 2 and K xFe 2-yS 2, and with similar contribution, implying that the phase ratio is not a decisive factor influencing the lack of superconductivity in the latter. Comparison of structural parameters of the Fe-vacancy-disordered model indicates that the replacement of selenium (Se) by sulphur (S) results in an appreciablemore » reduction in the Fe-Ch interatomic distances and anion heights, while simultaneously increasing the irregularity of FeCh 4 tetrahedra, suggesting the more significant influence of these factors. Finally, structural features are also compared to the non-intercalated FeSe and FeS parent phases, providing further information for the discussion about the influence of the lattice degrees of freedom on the observed properties in layered iron chalcogenides.« less
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  1. Inst. of Electronic Structure and Laser (IESL), Foundation for Research and Technology- Hellas (FORTH), Vassilika Vouton, Heraklion (Greece)
  2. Brookhaven National Lab. (BNL), Upton, NY (United States). Condensed Matter Physics and Materials Science Dept.
  3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Neutron Scattering Division
Publication Date:
Report Number(s):
Journal ID: ISSN 2410-3896
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Condensed Matter
Additional Journal Information:
Journal Volume: 3; Journal Issue: 3; Journal ID: ISSN 2410-3896
Research Org:
Brookhaven National Laboratory (BNL), Upton, NY (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; neutron pair distribution function (PDF); intercalated iron superconductors; anion height; tetrahedron regularity
OSTI Identifier: