Formation mechanism of superconducting phase and its three-dimensional architecture in pseudo-single-crystal KxFe2-ySe2
- Ames Lab., Ames, IA (United States)
- Ames Lab., Ames, IA (United States); Iowa State Univ., Ames, IA (United States)
- Carl Zeiss Microscopy, LLC, Peabody, MA (United States). Ion Microscopy Innovation Center (IMIC)
- Carl Zeiss Microscopy, LLC, Thornwood, NY (United States)
- Oxford Instruments America, Inc., Concord, MA (United States)
Here, we report how the superconducting phase forms in pseudo-single-crystal KxFe2-ySe2. 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 KxFe2-ySe2 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 electron 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.
- Research Organization:
- Ames Lab., Ames, IA (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES)
- Grant/Contract Number:
- AC02-07CH11358
- OSTI ID:
- 1249341
- Alternate ID(s):
- OSTI ID: 1237792
- Report Number(s):
- IS-J-8950; PRBMDO
- Journal Information:
- Physical Review B, Vol. 93, Issue 6; ISSN 2469-9950
- Publisher:
- American Physical Society (APS)Copyright Statement
- Country of Publication:
- United States
- Language:
- English
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