NEUTRON-DIFFRACTION STUDY ON THE CRYSTAL-STRUCTURE OF LITHIUM INTERCALATED CHEVREL PHASES

High resolution neutron diffraction results determined the relative positions and relative occupancies of small atom sites in the Chevrel phase system LiXMo6S8 in dependence of the lithium content of the ternary compounds. It was shown that the inner sites get exclusively occupied in LilMo6S8. These inner sites are still occupied by 1 atom per ring in Li3Mo6S8 and Li4Mo6S8 the remaining 2 resp. 3 guest atoms being placed on outer sites. The remarkable role of Li3Mo6S8 as known from NMR measurement of the Li-7-lineshift was related to the exceptional close geometrical situation of Li1 and Li2 sites allowing an easy diffusion within the network of interstitial sites and the formation of symmetric (Li3)2+-clusters with intracluster distances va in between 2.3 angstrom and 4.0 angstrom.