Force constants and thermodynamical properties of layered SnSeδS2-δ (0≤δ≤2)

Lattice dynamics of SnSeδS2-δ (0≤δ≤2) mixed compounds have been investigated by Raman scattering and infrared absorption spectroscopy. A linear-chain model has been used for analyzing the phonon frequencies and obtaining the variation of the force constants as a function of composition. From the Debye definition of a partition function of a solid, some thermodynamical properties have been calculated. An almost linear behavior has been obtained for the evolution of the Helmholtz free energy, entropy, internal energy and heat capacity as a function of composition, δ, in SnSeδS2-δ at room temperature. Experimental results obtained at different temperatures have allowed us to calculate these thermodynamical properties as a function of T and to obtain the Debye temperature.