2011/04/28 by J. Q. Li, Y. J. Song, Li, J. Q. +15
Materials Science · #FOS: Physical sciences #Iron-based superconductors research #Superconductivity (cond-mat.supr-con)
paper · pdf · doi:10.48550/arxiv.1104.5340
openalex publication_date 2011/04/28 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/28
The Fe-based superconducting KxFe2-ySe2 (0.6 \leg x \leg 1, 0.2\leg y \leg 0.4) compounds, unlike the well-known RFe2As2 (R = Ba, Sr, Ca) superconductors, contain complex structural features and notable physical properties, such as the Fe-vacancy ordering, multi-superconducting transitions and the phase separation[1]. Recent experimental studies also suggested the presence of remarkable interplay among the Fe-vacancy order and the antiferromagnetic structure[2]. Here we demonstrate that the well-characterized superconducting KxFe2-ySe2 (0.6 \leg x \leg 0.8, 0.2 \leg x \leg 0.3) samples contain complex microstructure features and undergo successive phase transitions at low temperatures. In-situ TEM observations on a number of the KxFe2-ySe2 superconductors demonstrated the presence of a remarkable collapse of the Fe-vacancy order above the superconducting transition, as a result, the superconducting phase actually adopts a tetragonal structure without the Fe-vacancy ordering. Moreover, our analysis at the low temperatures suggests that the superconductors likely adopt a Fe-deficient structure with composition of K0.75Fe2-ySe2. These results are important not only for the further optimization of superconducting phase in present system but also for understanding the mechanism of the Fe-based superconductivity.