title: Large local disorder in superconducting K(0.8)Fe(1.6)Se2 studied by extended x-ray absorption fine structure.
abstract: We have measured the local structure of superconducting K(0.8)Fe(1.6)Se(2) chalcogenide (T(c) = 31.8 K) by temperature dependent polarized extended x-ray absorption fine structure (EXAFS) at the Fe and Se K-edges. We find that the system is characterized by a large local disorder. The Fe-Se and Fe-Fe distances are found to be shorter than the distances measured by diffraction, while the corresponding mean square relative displacements reveal large Fe-site disorder and relatively large c-axis disorder. The local force constant for the Fe-Se bondlength (k ~ 5.8 eV Å(-2)) is similar to the one found in the binary FeSe superconductor, however, the Fe-Fe bondlength appears to be flexible (k ~ 2.1 eV Å(-2)) in comparison to the binary FeSe (k ~ 3.5 eV Å(-2)), an indication of partly relaxed Fe-Fe networks in K(0.8)Fe(1.6)Se(2). The results suggest a glassy nature for the title system, with the superconductivity being similar to that in the granular materials.
authors.affiliation: Dipartimento di Fisica, Università di Roma La Sapienza, Piazzale Aldo Moro 2, 00185 Roma, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Iadecola
authors.forename: B
authors.initials: B
authors.lastname: Joseph
authors.forename: L
authors.initials: L
authors.lastname: Simonelli
authors.forename: A
authors.initials: A
authors.lastname: Puri
authors.forename: Y
authors.initials: Y
authors.lastname: Mizuguchi
authors.forename: H
authors.initials: H
authors.lastname: Takeya
authors.forename: Y
authors.initials: Y
authors.lastname: Takano
authors.forename: N L
authors.initials: NL
authors.lastname: Saini