Phase transitions and metastable states in TlGaSe₂

Incommensurate phase properties of TlGaSe2layered crystals

“…On cooling, TlGaSe 2 crystal undergoes a second order phase transition from a paraelectric phase to an incommensurate phase at the temperature Ti~242 K. According to dielectric measurements, the results show that the phase transition temperature at 242 K is an incommensurate phase transition [11]. The temperature dependence of the real and imaginary parts of the dielectric constant of TlGaSe 2 shows previously reported well-known anomalies at the phase transition temperatures of 108 K and 115 K (figure 1).…”

“…The temperature dependence of the real and imaginary parts of the dielectric constant of TlGaSe 2 shows previously reported well-known anomalies at the phase transition temperatures of 108 K and 115 K (figure 1). In addition, the real part of the dielectric constant exhibits slight anomaly corresponding a weak ferroelectricity at 65 K [11,12]. According to structural investigations [13], the transition to the incommensurate phase is associated with ____________________ condensation of a soft mode at a point in the Brillouin zone characterized by q i (δ,δ,0.25), where δ is the incommensuration parameter (δ= 0.02).…”

Influence of Isomorphic Atom Substitution on Lattice Anisotropy of Thallium Dichalcogenide Layered Mixed Crystals

“…Now let us consider the variation of the lattice volume on the compositions of the mixed crystals studied. It is well known from the literature that TlGaSe 2 and TlInS 2 sequentially undergo low-temperature transitions to an incommensurate phase and a ferroelectric phase at T i = 115 K, T c = 108 K and T i = 213 K, T c = 189 K, respectively [8][9][10][11]. However, in TlGaS 2 crystals no evidence for a soft mode behavior has been found.…”

Electron-Deformational Phase Transitions in a TlGaSe2Layered Crystal

“…In this crystal transitions from the high temperature paraphase to the incommensurate phase at T i = 118 K, and then to the commensurate ferroelectric phase at T c = 108 K, as well as the existence of additional metastable phases [2] have been identified. Additionally, based on experimental investigations, it has been shown that TlGaSe 2 possesses unusual electrical and optical characteristics [3][4][5][6].…”

“…Recently, a ternary layered TlGaSe 2 crystal has attracted considerable interest due to its ferroelectric and semiconducting properties as well as sequences of the structural phase transition [1,2]. In this crystal transitions from the high temperature paraphase to the incommensurate phase at T i = 118 K, and then to the commensurate ferroelectric phase at T c = 108 K, as well as the existence of additional metastable phases [2] have been identified.…”