Behavior of the layered crystals TlInS2 and TlGaSe2 near phase transitions in a static electric field

Abstract

The effect of an orienting electric field on the anomalies of the temperature dependence of the dielectric constant ε of the crystals TlInS2 and TlGaSe2 and of the pyroelectric current i in TlInS2 near phase transitions is investigated. It is found that the ε(T) profile of both crystals undergoes the same transformation at the point of the phase transition to the incommensurate phase under the influence of a static electric field applied in the plane of the layer. It is established that the maximum of ε(T) in TlGaSe2 and of i(T) in TlInS2 at the point of the phase transition to the commensurate polar phase is shifted in a certain range of orienting electric fields and that the sign of the temperature shift depends on the value of the external electric field. An interpretation is offered for the experimental results.

Phase relations in ferroelectric/ferromagnetic TlInS2–TlCoS2 and TlGaSe2–TlCoSe2 systems

“…2. As it is seen from the figure, the temperature dependence curve ε(T) of TlGaSe 2 contains maxima, in connection to the phase transition points in IC phase at T = 117.2 K, and C ferroelectric phase at T c = 114 K. In both TlInS 2 and TlGaSe 2 crystals, the temperature curves ε(T) in the paraelectric, and ferroelectric phases are well approximated by Curie-Weiss law with the value of Curie constant of about 10 3 K. It is noted, that temperature state of the anomalies on the curve ε(T), and the value of Curie constant TlGaSe 2 are also well agreed with the results obtained by others [17,[29][30][31].…”

“…1. As it is seen from the figure, the curve ε(T) is characterized by anomalies at 206.3 K and 202.4 K, and near 201 K. Comparing our results with the data, given in [15][16][17][18][27][28], one can conclude that the temperature dependence of the dielectric constant ε(T) of TlInS 2 differs from the analogical curves given in the literature both by the number of anomalies, and their temperatures. Taking into consideration the results of [28], in which the strong dependence of the PT temperatures of TlInS 2 on defects, and impurities in the crystal structure of the samples had been obtained, one can propose that the anomalies of ε(T) observed at 206.3 K and 202.4 K are connected with PT to IC, and C phases, respectively.…”

“…The first investigations of semiconductor properties of TlInS 2 and TlGaSe 2 were performed by the authors of [13][14]. Later dielectric properties, and ferroelectric phase transitions in the same compounds were studied [15][16][17][18]. Besides, investigations of magnetic properties of the isostructural compounds revealed the presence of ferromagnetic ordering in TlCrS 2 , TlCrSe 2 [19][20], ferrimagnetic state in TlCoS 2 and TlCoSe 2 [21], antiferromagnetic ordering in TlFeS 2 , TlFeSe 2 , TlMnS 2 , TlMnSe 2 [22][23][24], as well as disorder structures (TlInS 2 , TlGaSe 2 ) [15][16][17][18]25].…”

“…Later dielectric properties, and ferroelectric phase transitions in the same compounds were studied [15][16][17][18]. Besides, investigations of magnetic properties of the isostructural compounds revealed the presence of ferromagnetic ordering in TlCrS 2 , TlCrSe 2 [19][20], ferrimagnetic state in TlCoS 2 and TlCoSe 2 [21], antiferromagnetic ordering in TlFeS 2 , TlFeSe 2 , TlMnS 2 , TlMnSe 2 [22][23][24], as well as disorder structures (TlInS 2 , TlGaSe 2 ) [15][16][17][18]25]. As it is known, on cooling TlInS 2 and TlGaSe 2 , the crystals undergo a sequence of the structural phase transitions (PT), including the PT in the incommensurate (IC), and commensurate (C) ferroelectric phases [15][16][17][18].…”

The magneto-dielectric properties of compounds and alloys in the systems of TlInS2–TlFeS2, TlInS2–TlFeSe2

“…1 the temperature dependence of the dielectric permittivity of TlInS 2 measured under the atmospheric pressure is given. As can be seen from figure, curve ε (T) is characterized by anomalies in the form of maximums at ∼206.3 K and ∼202.4 K, and also by the presence of small "bend" around 201 K. It is known that with a temperature decrease under the atmospheric pressure the layered crystal TlInS 2 experiences the complex sequence of structural phase transitions (PT), including PT in the incommensurate (IC) and commensurate (C) ferroelectric phases [4][5][6][7]. The initial paraelectric phase of TlInS 2 posseses monoclinic crystalline structure that is characterized by space group of symmetry C 6 2h [8].…”