RAMAN AND INFRARED VIBRATIONAL-SPECTRA OF TLGAS2 CRYSTALS

An investigation was made of the Raman scattering in TlGaS2 crystals, which were oriented in different geometries, and of the temperature dependences of such scattering at 77-400 K. A phase transition was found: it altered the polarization dependences of the vibrational modes, caused line splitting, weakened some and enhanced other vibrational modes when temperature was lowered. An investigation was made of the vibrational reflection spectra in the range 4000-50 cm-1. Polar vibrational LO and TO modes as well as their principal parameters were identified. A calculation was made of the effective Szigeti charge, of the dynamic Born charge, and of the relative effective charge of the anions and cations using the data obtained from the E parallel-to a and E parallel-to b polarizations in TlGaS2 crystals. It was found that the ionicity of the cations and anions was different along the a and b axes.