Anisotropic phonon dispersion in GaS

The group theoretical analysis of lattice vibrations in GaS and neutron inelastic scattering measurements of acoustic phonons propagating along the Delta , Sigma and T directions are presented. The elastic constants C11, C33, and C44 are derived and the results for the Delta direction are analysed to determine interlayer force constants. The frequencies of the B1 modes along Sigma and T show a weak quadratic dependence on wavevector. A simple interatomic force model is fitted to the phonon frequencies, and the frequency distribution function is calculated. The temperature dependence of the lattice specific heat and of the corresponding Debye temperature is calculated; over a small temperature range the variation of the specific heat is characteristic of a pseudo-two-dimensional solid.

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