DETERMINATION OF THE LOW-TEMPERATURE 2D AND 3D STRUCTURES OF THE 2ND STAGE CESIUM GRAPHITIDE

The structure of stage-2 cesium derivatives CsC24 was investigated usi ng X-ray diffraction. The 2D and 3D arrangements of the cesium atoms i n pure CsC24 were deduced from Laue diffractograms and rotating crysta l patterns. Below 165K, the 2D structure is formed mainly of a 2.54 x 2.59 R 14.5 degrees incommensurate structure with 2 x 2 R 0 degrees co mmensurate domains. At 140 K, while the cesium incommensurate layers g et 3D stacked, the 2 x 2 R 0 degrees commensurate layers are randomly distributed in the structure. The incommensurate cesium layers are arr anged in a 2D modulated stacking, but at lower temperatures this struc ture is partially replaced by a rhombohedral stacking in which the ces ium atoms are modulated along the c-axis owing to the dominating influ ence of graphitic host. In slightly oxidized compounds, the presence o f impurities induces the formation of additional 2.23 x 2.23 R 25.5 de grees incommensurate domains which are separated from the structures a lready observed in pure compounds. These stage-2 domains of compositio n CsC20 are characterized by a large interlayer distance. We suggest t hat oxygen suboxide impurities at the edge of the domains are at the o rigin of this particular dense structure.