X-ray-edge studies and photoemission of MnxSn1-xMo6S8.

Abstract

X-ray-absorption and -photoemission studies were carried out on the manganese-doped Chevrel-phase compound ${\mathrm{Mn}}_{\mathrm{x}}$${\mathrm{Sn}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Mo}}_{6}$${\mathrm{S}}_{8}$ for x=0.1, where a maximum superconducting transition temperature ${T}_{c}$ occurs. With use of synchrotron radiation and x-ray fluorescence, near-edge-absorption and extended x-ray-absorption fine-structure (EXAFS) spectra were obtained at the K edge of Mn in the doped compound. The results indicate that each manganese atom, surrounded by eight sulfur atoms, substitutes for tin at the center of a large cavity in ${\mathrm{SnMo}}_{6}$${\mathrm{S}}_{8}$. The manganese-sulfur nearest-neighbor distance is found to be 2.02\ifmmode\pm\else\textpm\fi{}0.05 A\r{}, somewhat less than 2.26 A\r{} for Sn in ${\mathrm{SnMo}}_{6}$${\mathrm{S}}_{8}$. The probable charge of manganese is found to be 4+ and, considering the valence-electron-charge model of charge transfer, this explains the observed maximum in ${T}_{c}$. The photoemission experiments yield an energy distribution curve for the valence band which is in good agreement with band theory.