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Neutron scattering investigation of layer-bending modes in alkali-metal—graphite intercalation compounds
Phys. Rev. B 26, 5919 – Published 15 November, 1982
DOI: https://doi.org/10.1103/PhysRevB.26.5919
Abstract
Phonon dispersion curves for low-frequency transverse modes propagating in the basal plane have been measured in the alkali-metal—graphite intercalation compounds K, Cs, K, and Rb by means of neutron spectroscopy. The acoustic branches show an almost quadratic dispersion relation at small , characteristic of strongly layered materials. The optical branches of stage-1 compounds can be classified as either graphitelike branches showing dispersion, or as almost dispersionless alkali-metal-like modes. Macroscopic shear constants and layer-bending moduli have been obtained for the intercalation compounds by analyzing the data in terms of a simple semicontinuum model. In stage-2 compounds, a dramatic softening of the shear constant by about a factor of 8 compared with pure graphite has been observed. Low-temperature results on K indicate the opening of a frequency gap near the alkali-metal Brillouin-zone boundary, possibly due to the formation of the alkali-metal superstructure.
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