Fe-site substitution effects on superconductivity and microstructure of phase-separated K_0.8Fe_1.75Se₂ superconductor

¹ School of Materials Science and Engineering, Hefei University of Technology - No. 193, Tunxi Road, Anhui Province, Hefei 230009, China
² Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences Beijing 100190, PRC

^(a) hxyang@aphy.iphy.ac.cn (corresponding author)
bo.zhang@hfut.edu.cn (corresponding author)

Received: 10 December 2013
Accepted: 19 February 2014

Abstract

Series of Fe-site–substituted K_0.8Fe_1.75−xM_xSe₂ (M = Cu, Ni, Mn, Zn, Co, Cr) single crystals of nominal composition have been prepared and microstructural features have been studied. Systematic Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM) investigations reveal that the substitution effect can be classified into two types: Ni, Co and Cr atoms can be homogenously doped into the superconducting stripes of the phase-separated K_0.8Fe_1.75Se₂ system, while the Cu, Mn and Zn atoms can hardly be introduced into the superconducting stripes, which instead give rise to the formation of new non-superconducting K-M-Se phases embedded in the sample. The complex physical measurement data reported in the literature can be nicely explained by the microstructure picture.