Low temperature structures of the second stage cesium graphitide and effect of trace impurities

Abstract

Stage 2 CsC 24 graphite-cesium derivatives were synthesized and characterized using x-ray diffraction. Pure CsC 24 specimens are single phase stage 2 in the range 77 -300 K. From the 00l scans, we observed on samples slightly polluted during the transfer in the glove box, the tridimensional segregation of stage 2 in a main CsC 26 structure and an additional dense CsC 20 structure. The 2D Laue diffraction photographs are the same as already reported, but are interpreted as a mixture of 2 3 2 R 0 ± lattice commensurate and 2.54 3 2.54 R 14.5 ± lattice incommensurate structures. In oxidized compounds, we identified another 2.23 3 2.23 R 25.5 ± 2D additional incommensurate structure corresponding to the composition CsC 20 already evidenced by analysis of the 00l diffractograms. We suggest that oxygen impurities are at the origin of this particular stiff and dense structure at low temperature.