X-ray study of the ordering of the alkali ions in the intercalation compounds NaxTiS2 and LixTiS2

Abstract The arrangement of the alkali ions in electrochemically intercalated TiS 2 crystals was studied by diffuse X-ray techniques. In Na x TiS 2 a stage 3 phase was discovered in addition to the known stage 1 and 2 phases. Three types of three-dimensionally ordered superstructures were observed: a ( 3 1 2 × 3 1 2 ) superstructure for stage 2 and 3 phases, a (2 × 2) and ( 2 × 3 1 2 ) superstructure for stage 1 and 2 phases. The appearance of these superstructures is consistent with a screened Coulomb interaction between the sodium ions. In the single-phase region above x = 1 2 , diffuse rings show up in addition to the ( 2 × 3 1 2 ) superlattice. These rings are caused by local rearrangements of the ions to accommodate the excess sodium ions. The ( 3 1 2 × 3 1 2 ) and (2 × 2) superstructures were also observed in Li x TiS 2 crystals.