C-axis lattice dynamical properties of AuCl3-GIC

Abstract

AuCl 3 -GIC has a significantly short c -axis lattice constant due to the planar molecule Au 2 Cl 6 intercalate which are tilted by 15 ° with respect to the graphitic layers. We report the specific heat, c -axis compressibility and thermal expansion of stage-1 AuCl 3 -GIC to clarify the lattice dynamics related to the AuCl 3 intercalates. Lattice specific heat deviates from ordinary T 3 dependence where the Debye temperature varies from 120–160 K, suggesting the presence of low energy phonons of heavy AuCl 3 intercalates as well as the acoustic phonons. Thus, the c -axis compressibility and the thermal expansion are analyzed in terms of one-dimensional Debye contribution of the longitudinal acoustic phonon and the libron modes associated with the rotation of the AuCl 3 intercalate. Θ D is estimated to be 440K, while the libron contribution, which plays a major role at low temperatures below 50K, is explained with the Einstein temperature Θ E = 33 K . The Gur̈neisen parameters are estimated to be Γ = 2.49 and Γ E = 0.46, concluding that the c -axis lattice expansion comes mainly from the c -axis longitudinal acoustic phonon, in spite of its lattice stiffness being much stronger than that expected for the libron mode.