Phononic and Elastic Properties of TlInS2 Crystals of Hexagonal Symmetry: Experiment and Ab Initio Calculations

The phononic properties of TlInS2 crystals of hexagonal symmetry have been investigated experimentally, using Raman scattering, and theoretically ab initio, using the density functional perturbation theory (DFPT). The frequencies of Raman-active optical modes were determined by analyzing the Raman spectra. The dispersion of phonon modes, origin of energy states, partial densities of states (PDOS) projected on atoms, and frequency of optical phonons are calculated ab initio. The elastic constants С11, С12, С13, С33, and С44 of TlInS2 crystals of hexagonal symmetry are also calculated, and their elastic moduli are determined, as well as the propagation velocities of longitudinal and transverse acoustic waves in different crystallographic directions. The Debye temperature is estimated.