Investigation of the Vibrational Spectra of a SbSI (Sb₂S₃)_0.15 Crystals in Harmonic and Anharmonic Approximations

Abstract

The vibrational spectra of SbSI (Sb₂S₃)_0.15 crystals in harmonic and anharmonic approximations are calculated by Density Functional Theory (DFT) method. Investigation of IR, R and A low frequency normal modes at points k = 0 and k = 0.5 of the Brillouin zone in SbSI (Sb₂S₃)_0.15 crystals reveal that soft behavior of these modes mainly depends on the temperature dependent force constant C_ij between Sb and I atoms and symmetry coordinates.

Investigation of the mean value potential energy _p(z) per one atom dependence on the amplitude of the soft mode B_1u symmetry coordinates in c (z) axis direction on the phase transition region have explained why ferroelectric phase transition temperature T_C depends on compression in x-y plane of the SbSI chains in SbSI (Sb₂S₃)_x crystals.

Keywords:

• SbSI (Sb₂S₃) _x crystals
• vibrational spectrum
• harmonic and anharmonic approximations