Investigation of the Vibration Spectra of a SbSBrxI1-x Crystal in Harmonic and Quasiharmonic Approximation

Abstract

The vibration spectra of SbSBrxI1-x (x = 0 ÷ 0.75) crystal have been determined in quasiharmonic approximation by diagonalization of dynamical matrix. Applying the model atom A with its own parameters (mass and force constant) we were able to get exact normal modes’ vibration frequencies. The obtained normal modes’ frequencies were superposed with experimental data. It is proved that in Brillouin zone's point k = 0 the lower frequency IR (infrared) mode of B1u symmetry and lower frequency R (Raman) mode of B1g symmetry are soft-alike modes whereas in Brillouin zone's point k = 0.5 an acoustic and Raman mode become active, but lower frequency IR mode becomes inactive. The interaction between phonons creates the anharmonicity of soft-alike IR, R and A vibration modes.