An X-ray crystallographic analysis was performed on an HOPG sample of stage-2 Rb-intercalated graphite (C24Rb) at room temperature. A q-scan in the circularly averaged (hk.0) reciprocal lattice plane shows the familiar liquid-like pattern with a suggestion of substrate modulation effects. Assuming partial registry of the Rb with its graphite host, an analysis of 85 Bragg peaks, to which a Rb contribution was included, was performed. The registered fraction (x) was thereby estimated to be 0.71+/-0.02. The in-plane combined thermal and static displacement amplitude of the assumed registered Rb atoms was 2>1/2 [congruent with] 0.32 A. This large amplitude suggests that the standard Debye-Waller treatment is inappropriate here and that substrate modulation effects on the 2-D liquid, as they appear at the graphite peaks, may be more important.
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http://deepblue.lib.umich.edu/bitstream/2027.42/25508/1/0000049.pdf