Vibrational Spectra and Phase Transitions in Layered Semiconducting Ferroelectrics with TlGaSe₂ Structure. I. Temperature Dependences of Parameters of the Raman Spectrum Lines of TlGaSe₂

Abstract

Yu. I. DURXEV et al.: Vibrational Spectra and Phase Transitions (I)

Urbach Tail and Optical Absorption in Layered Semiconductor TlGaSe2(1-x)S2xSingle Crystals

“…We have decided that these values (90-100, 100, 100-120, 160-180, 220-240 and 240-250 K) obtained from the band gap energy change may be phase transition temperatures. The presence of phase transition temperature in TlGaSe 2(1−x) S 2x at some temperatures given Table II was also confirmed by temperatures given in the literature [14,[23][24][25][26][27][28].…”

“…The dielectric and optical anomalies of TlGaSe 2 indicate structural changes at T ∼ = 120 K and 107 K [14,24]. The presence of the phase transitions at 246 K and 101 K were confirmed by means of the heat capacity measurement [25,26]. The temperature dependence of C p of TlGaS 2 single crystal was obtained in the range 60-260 K during heating.…”

The Effect of Fe on the Absorption Spectra in TlGaS2, TlGa0.99Fe0.01S2 and TlGa0.98Fe0.02S2 Layer Single Crystals

“…The long-wavelength tail of the optical absorption in TlGaSe 2 at a ¼ 30-150 cm --1 is shown to obey the Urbach rule in the temperature range 4.2-293 K [8,9]. The anomalous behaviour of the parameters of this rule suggests the presence of two phase transitions in TlGaSe 2 at 246 and 101 K in addition to the known phase transitions at 120 and 107 K. The presence of the phase transitions at 246 and 101 K is also confirmed by means of heat capacity measurement [8,9].…”

Structural and electrical properties of TlGa(SxSe1−x)2 mixed crystals

“…Since the structure of A 3 B 3 C 6 layer crystals, such as TlGaSe 2 , TlGaS 2 , TlInSe 2 and TlInS 2 were generally assigned as tetragonal or monoclinic with space group C 6 2h , and its pseudotetragonality was attributed to the presence of micro twins [4,20]. It was reported that this ambiguity of this class of compounds may also be related with different possible versions of layer stacking [2].…”

“…But most of them are focused on the study of phase transitions of these layer crystals, such as TlGaSe 2 [4], TlGaS 2 [4,5], and TlInS 2 [2,[6][7][8]. The crystallographic data on these compounds have been ambiguous * Corresponding author.…”