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Title: Formation mechanism of superconducting phase and its three-dimensional architecture in pseudo-single-crystal K xFe 2-ySe 2

Here, we report how the superconducting phase forms in pseudo-single-crystal K xFe 2-ySe 2. In situ scanning electron microscopy (SEM) observation reveals that, as an order-disorder transition occurs, on cooling, most of the high-temperature iron-vacancy-disordered phase gradually changes into the iron-vacancy-ordered phase whereas a small quantity of the high-temperature phase retains its structure and aggregates to the stripes with more iron concentration but less potassium concentration compared to the iron-vacancy-ordered phase. The stripes that are generally recognized as the superconducting phase are actually formed as a remnant of the high-temperature phase with a compositional change after an “imperfect” order-disorder transition. It should be emphasized that the phase separation in pseudo-single-crystal K xFe 2-ySe 2 is caused by the iron-vacancy order-disorder transition. The shrinkage of the high-temperature phase and the expansion of the newly created iron-vacancy-ordered phase during the phase separation rule out the mechanism of spinodal decomposition proposed in an early report [Wang et al, Phys. Rev. B 91, 064513 (2015)]. Since the formation of the superconducting phase relies on the occurrence of the iron-vacancy order-disorder transition, it is impossible to synthesize a pure superconducting phase by a conventional solid state reaction or melt growth. By focused ion beam-scanning electronmore » microscopy, we further demonstrate that the superconducting phase forms a contiguous three-dimensional architecture composed of parallelepipeds that have a coherent orientation relationship with the iron-vacancy-ordered phase.« less
 [1] ;  [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [2]
  1. Ames Lab., Ames, IA (United States)
  2. Ames Lab., Ames, IA (United States); Iowa State Univ., Ames, IA (United States)
  3. Carl Zeiss Microscopy, LLC, Peabody, MA (United States). Ion Microscopy Innovation Center (IMIC)
  4. Carl Zeiss Microscopy, LLC, Thornwood, NY (United States)
  5. Oxford Instruments America, Inc., Concord, MA (United States)
Publication Date:
OSTI Identifier:
Report Number(s):
Journal ID: ISSN 2469-9950; PRBMDO
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Physical Review B
Additional Journal Information:
Journal Volume: 93; Journal Issue: 6; Journal ID: ISSN 2469-9950
American Physical Society (APS)
Research Org:
Ames Laboratory (AMES), Ames, IA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States