Dipartimento di Fisica, Università di Roma La Sapienza, Piazzale Aldo Moro 2, 00185 Roma, Italy.
J Phys Condens Matter. 2012 Mar 21;24(11):115701. doi: 10.1088/0953-8984/24/11/115701. Epub 2012 Feb 21.
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.
我们通过在 Fe 和 Se K 边缘的温度相关极化扩展 X 射线吸收精细结构（EXAFS）测量了超导 K(0.8)Fe(1.6)Se(2) 硫族化物（T(c) = 31.8 K）的局域结构。我们发现该系统的局域无序很大。Fe-Se 和 Fe-Fe 距离比衍射测量的距离短，而相应的均方根相对位移显示出较大的 Fe 位无序和相对较大的 c 轴无序。Fe-Se 键长的局部力常数（k ~ 5.8 eV Å(-2)) 与二元 FeSe 超导体中的力常数相似，然而，Fe-Fe 键长似乎比二元 FeSe（k ~ 3.5 eV Å(-2)) 更具弹性（k ~ 2.1 eV Å(-2))，表明 K(0.8)Fe(1.6)Se(2) 中部分弛豫的 Fe-Fe 网络。结果表明该体系具有玻璃态性质，超导性类似于颗粒材料中的超导性。
