Fe-site substitution effects on superconductivity and microstructure of phase-separated K0.8Fe1.75Se2 superconductor

Series of Fe-site-substituted K0.8Fe1.75-xMxSe2 ( 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 K0.8Fe1.75Se2 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. Copyright (C) EPLA, 2014