Electric Conductivity of TlInS2, and TlGaSe2, Crystals in the Region of Phase Transitions

Abstract

The semiconductive nature of the electric conductivity of TllnS2 and TlGaSe2 laver c r v s t a l s was f i r s t reported in /l/. The possibilitv of second-order phase transitions (PT) in these crystals was theoreticallv predicted much later /2/.When studying IR-reflection spectra, a soft ferroelectric mode was found in TllnS2 /3/ and TlGaSe2 /4/. Resides, anomalies were recorded in the tempera t u r e behaviour of thermal expansion /5, 6/, heat capacity /7, 8/, and optical properties /9, 10/ of TlInS2 (189 to 220 K) and TlGaSe2 (100 to 120 K) crystals, respectively. At present it is thought to be an established fact that a PT to a commensurate phase takes place in these crystals. Put this transition is effected through an intermediate incommensurate phase. The sequence of phases and P T s in TlInS2 and TlGaSe2 crystals is diagrammed in Fig. 1. Despite the existence of a great body of accumulated information on PTs in T11nS2 and TlGaSe2, the nature of their effect on the electronic subsystem in these crystals remains unclear. The present report gives experimental results on the behaviour of the electric conductivities of TlInS2 and TlGaSe single crystals in the vicinity of the phasetransition region. 2 T11nS2 and TlGaSe2 single crystal ingots were grown by us from melts by the Eridgman-Stockbarger method. Fused-in indium served as ohmic contacts f o r the specimens. Measurements were conducted in a helium cryostat with a system of thermal stabilization in the direction of crystal cooling, which ruled out the influence of thermal depletion of localized levels, as distinct from the results of another study /lo/.Fig. 2 depicts the temperature dependences of electric conductivity along ( da' and a c r o s s ( d ) the layers in T11nS2. In the low-temperature region the C --1) Prospekt Narimanova 33, 370143 Baku, USSR. 9 phvsica (a)

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

“…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.…”

Some special dielectric characteristics of TlGaSe2 layered crystals

“…TlGaSe 2 is a member of this family. The crystal is a promising material due to its very attractive thermodynamic [1], optic [2,3], acoustic [4], electric [5,6] and mechanic [7]. TlGaSe 2 was reported to have a monoclinic structure with the group of C2/c at room temperature [8].…”

Incommensurate phase properties of TlGaSe2layered crystals

“…There has been a growing interest for TlGaSe 2 layered crystal due to its very attractive optic [1,2], electric [3,4], crystallographic [5], mechanic [6], thermodynamic [7] and acoustic [8] properties. However, the earlier studies focused on the physical properties in the temperature range 90-140 K. That is why the crystal undergoes successive phase transitions.…”