Local structure of the superconductor K 0.8Fe 1.6+xSe 2: Evidence of large structural disorder

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

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Abstract

The local structure of superconducting single crystals of K 0.8Fe 1.6+xSe 2 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 LaFeAsO 0.89F 0.11, having the same effective Einstein temperature (stiffness). In K 0.8Fe 1.6+xSe 2, the nearest-neighbor Fe-Fe bonds have a lower Einstein temperature and higher structural disorder than in LaFeAsO 0.89F 0.11. 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.

Original languageEnglish (US)
Article number024504
JournalPhysical Review B - Condensed Matter and Materials Physics
Volume85
Issue number2
DOIs
StatePublished - Jan 3 2012

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics

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