Effect of oxygen impurities on properties of the ternary superconductorSnMo6S8: Extended x-ray-absorption fine-structure determination of bond distances and local-density cluster calculations

Electronic structure calculations were performed for clusters representing the Chevrel-phase ${\mathrm{SnMo}}_6$ ${\mathrm{S}}_8$, with and without oxygen doping. In order to obtain the local structure around the Sn atom, extended x-ray-absorption fine-structure (EXAFS) measurements were made with synchro- tron radiation. The interatomic distances obtained experimentally were used in the calculations. The effect of oxygen doping on the Mössbauer isomer shift and quadrupole splitting values of ${}_{}{}^{119}{}_{}{}^{}\mathrm{Sn}$ was investigated theoretically and compared with reported experimental values. The effect of oxygen substitution on the density of states at the Fermi energy of the [${\mathrm{Mo}}_6$ ${\mathrm{S}}_8$ ${]}^{2\mathrm{-}}$ cluster was also studied. The results suggest that oxygen doping does not alter significantly the electronic structure of ${\mathrm{SnMo}}_6$ ${\mathrm{S}}_8$.