E. Mcrae et al., Raman light scattering and c-axis resistivity evidence for a pressure-induced stage transformation in PdAl2Cl8 intercalated graphite, PHYS REV B, 62(20), 2000, pp. 13757-13766
We have examined several samples of first- to third-stage PdAl2Cl8-intercal
ated graphite under hydrostatic pressures up to 1 GPa. In stage-1 highly or
iented pyrolytic graphite-(HOPG) and single-crystal-graphite-based material
s, the c-axis resistivity decreases sharply above a few kilobars; pressure
release induces a reversible return to the initial value only in the case o
f the latter sample. Raman spectra taken in situ under pressure on a HOPG-b
ased material show similarly irreversible effects. Analysis of the spectra
taken on higher-stage samples leads to the conclusion that hydrostatic pres
sure beyond a few kilobars increases the density of the intercalate within
the graphitic galleries, transforming the initial sample to a higher-stage
material. Since there is no loss of intercalate, the overall intercalate-to
-host charge transfer remains constant so that the Raman frequency is appro
ximately the same for both first- and second-stage products. This is an unu
sual situation in which there is thus an apparent lack of Raman signature i
n spite of the stage change.