Neutron scattering studies of alkali metal--graphite intercalation compounds Page: 4 of 11
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This pattern shows broad maxima which do not peak at simple
4
fractions of c*, and, although suggestive of a3y stacking,
is more characteristic of a mixture of structures or a disordered
state. The middle trace, taken at 721 K, shows that in addition
to a sharpening of the Bragg peaks, a phase transition has
occurred. The peaks at c* = 0.5 and 1.0 imply an a3 stacking
of the metal layers. We found no evidence for de-intercalation
at 721 K, due presumably to the fact that the compound and its
ampoule were at the same temperature. The upper trace was again
taken at 290 K, but after several days at 721 K. The pattern is
now representative of a3y6 stacking, with Bragg peaks at
c* = 0.25, 0.5 and 0.75 as had been found in early x-ray studies."*
The structure factor for the c* = 1 diffraction vanishes.
A more complete set of spectra is shown schematically in
Fig. 2. Additional results at 747 K are also shown, in this case
indicative of a liquid-like or highly disordered structure for the
metal atoms. No transitions were observed below 290 K. In total,
then, four different phases were observed for CgRb at and above
room temperature. In each case the transitions were not sharp,
and the patterns showed a mixture of two phases at some temperatures.
Furthermore, the onset temperature for appearance or disappearance
of a phase was not reproducible upon cycling the temperature.
These initial results for CgRb can be summarized as follows:
a number of different structures exist and it is therefore important
to measure the (h0&) reflections to establish the actual state of
the sample. In addition, there are indications that the structure
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Ellenson, W.D.; Semmingsen, D. & Fischer, J.E. Neutron scattering studies of alkali metal--graphite intercalation compounds, article, January 1, 1977; Upton, New York. (https://digital.library.unt.edu/ark:/67531/metadc1074113/m1/4/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.