Phase transitions and Raman scattering spectra of TlGaSe2

In this work we examined the phase transitions in the ternary thallium chalcogenide TlGaSe2 by studying the temperature dependence of the Raman spectra with the aid of confocal microscopy. The unpolarized Raman scattering spectra of TlGaSe2 single crystals were measured over the temperature range 78 300 K (which includes the range of the successive phase transitions) in the frequency region of 50 300 cm(-1). The Raman spectra exhibited 12 lines at 300 K, but the number of lines rose to 17 at 78 K. In the temperature interval between 107 K and 120 K, where the phase transitions take place, the temperature dependence of the phonon frequencies showed discontinuities for several of the Raman lines.