c-Axis Compressibility and Thermal Expansion of Gold Trichloride-Graphite Intercalation Compounds (AuCl₃-GICs)

Abstract

We investigated c-axis compressibility and thermal expansion of the first and the second stage AuCl₃-GICs in order to clarify the c-axis lattice dynamical properties related to the specific structure of AuCl₃ intercalates. The results are explained in terms of not only the (00l) longitudinal acoustic phonons but also the libron mode, in which the libronic motion of planar Au₂Cl₆ molecules plays an important role, in the case of the first stage compound. The acoustic phonon analyzed based on one-dimensional Debye model gives the Debye temperature Θ_1dD=444, K with the Grüneisen constants Γ=2.49, while the contribution of the libron has the characteristic energy of Θ_E=33, K and the Grüneisen constant Γ=0.46. c-axis thermal expansion of the second stage compound is explained in terms of the acoustic and the high energy optic phonon modes which have Θ_1dD=306, K and Θ_E=320, K, respectively, since the c-axis zone folding makes the energy of the optic phonon mode lowered.