Local structure of the superconductor K0.8Fe1.6+xSe2: Evidence of large structural disorder

T. A. Tyson; T. Yu; S. J. Han; M. Croft; G. D. Gu; I. K. Dimitrov; Q. Li

doi:10.1103/PhysRevB.85.024504

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Local structure of the superconductor K0.8Fe1.6+xSe2: Evidence of large structural disorder

T. A. Tyson, T. Yu, S. J. Han, M. Croft, G. D. Gu, I. K. Dimitrov, Q. Li

DOI 10.1103/PhysRevB.85.024504 · Physical Review B

T1

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Abstract

The local structure of superconducting single crystals of K0.8Fe1.6+xSe2 with Tc = 32.6 K was studied by x-ray absorption spectroscopy. Near-edge spectra reveal that the average valence of Fe is 2+. The room temperature structure about the Fe, K, and Se sites was examined by iron, selenium, and potassium K-edge measurements. The structure about the Se and Fe sites shows a high degree of order in the nearest-neighbor Fe-Se bonds. On the other hand, the combined Se and K local structure measurements reveal a very high level of structural disorder in the K layers. Temperature-dependent measurements at the Fe sites show that the Fe-Se atomic correlation follows that of the Fe-As correlation in the superconductor LaFeAsO0.89F0.11, having the same effective Einstein temperature (stiffness). In K0.8Fe1.6+xSe2, the nearest-neighbor Fe-Fe bonds have a lower Einstein temperature and higher structural disorder than in LaFeAsO0.89F0.11. The moderate Fe site and high K site structural disorder is consistent with the high normal state resistivity seen in this class of materials. For higher shells, an enhancement of the second-nearest-neighbor Fe-Fe correlation is found just below Tc, possibly due to changes in magnetic or local structural ordering.

Source-reported materials — not catalogue approval

Formula	Reported Tc (K)	Pressure (GPa)	Type
K0.8Fe1.6+xSe2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	32.6	Pressure not reported	onset
K0.8Fe1.6+xSe2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	32.6	Pressure not reported	onset
LaFeAsO0.89F0.11 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	—	Pressure not reported	unknown
LaFeAsO1-xFx Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	—	Pressure not reported	unknown
SmFeAsO1-δ Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	55	Pressure not reported	unknown
AFe2As2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	38	Pressure unresolved	unknown
LiFeAs Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	18	Pressure not reported	unknown
FeSe1-x Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	8	Pressure unresolved	unknown
FeSe1-x Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	37	7 GPa	unknown
AxFeySe2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	31	Pressure not reported	unknown