Valence and delocalization of yb in the Chevrel-phase YbMo 6 S 8

Mãssbauer isomer-shift measurements show that Yb is divalent in YbMo6Sg. The asymmetry of the Yb thermal vibration at 4.2 K obtained from the Goldanskii-Karyagin effect is much smaller than that obtained from a Rietveld refinement of neutron powder diffraction data at 16 K. This suggests that the displacement of Yb off the origin includes a significant, ~0.1-Å, static component which persists at low temperature. Full structural refinements at 16, 77, and 295 K show several interesting structural changes versus temperature