Investigation of the vibration spectra of a SbSBrxI1-x crystal in harmonic and quasiharmonic approximation

The vibration of spectra 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 constants) 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 B1a symmetry and lower frequency R (Raman) mode of B 1g symmetry are soft -alike modes whereas in Brilloun zone's point k = 0.5 an acoustic and Raman mode become active, but lower frequency IR mode becomes inactive. The interaction between phonones creates the anharmonicity of soft-alike IR, R and A vibration modesVytauto Didžiojo universitetasŠvietimo akademij