Brillouin Scattering Studies on Elastic Constants and Polytypes in GaSe_1-xS_x(0≤x≤1) Layered Crystals

Abstract

Brillouin scattering measurements have been made to determine a complete set of elastic tensor components in GaSe 1- x S x (0≤ x ≤1) layered crystals. It is found that most elastic tensor components exhibit discontinuities at the compositions x ≈0 and/or x ≈0.4, associating with the ε -γ and γ-β polytype transformations. With a simple layered structure model, the diagonal components of the elastic tensor are related to the inter- and intra-layer force constants. The composition and polytype dependences of the compressive and shear interlayer force constants are discussed by taking account of the Van der Waals interactions and the Coulomb interactions between two atoms in adjacent layers.