DIRECTIONAL DEPENDENCE OF EXTRAORDINARY INFRARED OSCILLATOR PARAMETERS OF TLGAS2-TYPE LAYER CRYSTALS

The directional dispersion of IR-active modes of TlGaS2, TlGaSe2 and TlInS2 layersingle crystals has been investigated, depending on the angle between the phonon wave vector q and the optical c-axis. Owing to the possibility of preparation crystals with various orientations of reflecting surfaces with respect to the optical c-axis, it was of interest to check the applicability of the generalized Born and Huang theory of long-wave optical vibrations in uniaxial crystals to TlGaS2-type layer crystals

INFRARED REFLECTIVITY SPECTRA OF TLGAS2-TYPE LAYER CRYSTALS

Infrared reflectivity spectra of TIGaS2, TIGaSe2 and TlInS2 layer crystals are measured for the polarization directions perpendicular and parallel to the optical c-axis in the spectral range from 20 to 400 cm-1. The optical dispersion parameters are obtained for both polarization directions. Besides, normal coordinates and effective force constants are determined for high-frequency lattice vibrations