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[en] Using the impedance spectroscopy methods the charge transfer in solid solution (TlGaSe2)1-x(TlInS2)x in the frequency range of 20-10''6 Hz before and after γ-irradiation with a dose of 0.25 MGy have been investigated. The relaxation character of dielectric constant dispersion and dielectric loss nature are established. The frequency dependence of the dielectric loss tangent (tgδ) in solid solution crystals (TlGaSe2)1-x(TlInS2)x is due not by only the relaxation polarization, but also by through conduction. The response rate is fp=10''3 Hs and the duration of the relaxation period is τ=10''-3s. It is found that the regularity σ∼ f''S (0,1 ≤S≤1,0) indicating on electric conduction on localized states takes place in frequency range 10''5 - 5·10''5 Hz for the electric conduction. The further frequency increase leads to the increase of ionic conductivity and to the system transition in the superionic state.
[en] Full text: TlGaTe2 has a quasi-one-dimensional layered structures and exhibit para-to-ferroelectric phase transitions through an intermediate incommensurate phase. TlGaTe2 exhibit nonlinear transport properties. This structure is body-centered tetragonal and features c-axis chains of atoms and edge-sharing GaTe4 tetrahedra. The TlGaTe2 monocrystals were grown by the modified Bridgman-Stockbarger method. The measurements were carried out on the sides perpendicular to polar axis. The sides were ground and covered by silver paste. Dielectric constant ?(T) and angle tangent of dielectric losses were measured by the alternating current bridge E7-8 (1 eHz), P5058 (10 eHz), E7-12 (1 IHz) and Tesla AI560 (100 eHz) in the temperature region 150-250 K. The velocity of temperature scanning was 0,1 K / min. The loops of dielectric hysteresis were studied at frequency 50 Hz using the modified circuit Soyer-Tauer. The pyroeffect has been investigated by the quasistatic method using universal voltmeter V7-30. The samples were irradiated (Co 60) at room temperature. The irradiation dose was accumulated through sequential exposures of the same sample and reached 100, 200, 300 and 400 Mrad. The dependences E (T) and Q (T) were measured after each exposure of the sample to irradiation. Conductivity was measured by the alternating current method. The temperature dependencies of dielectric constant E (T) of TlGaTe2 crystals at different frequencies are measured. It is known, that the presence of an impurity in the semiconductor results in occurrence of local states near the Fermi level. On these local states the hopping mechanism of charge transport is realized, which essentially influences both on electrical, and dielectrically properties of semiconductor-ferroelectrics. TlGaTe2. According to the temperature dependencies of dielectric constant E (T) study, TlGaTe2 has temperature instabilities of the crystal lattice lead to ferroelectric ordering
[en] The effect of γ-radiation on the optical properties of layered TlGaSe2 and TlInS2 crystals has been studied within a wavelength range of 400–1100 nm at 300 K. By means of analysis of optical absorption spectra, the energies of direct and indirect optical interbend transitions before and after γ-irradiation have been determined. It has been shown that the energies of direct and indirect nonforbidden optical transitions grow with accumulation of γ-radiation dose within 0–25 Мrad in TlGaSe2 and TlInS2 single crystals from Egd = 2.06 eV and Egi = 1.90 eV at D = 0 Мrad to Egd = 2.11 eV and Egi = 1.98 eV at D = 25 Мrad for TlGaSe2 crystals and from Egd = 2.32 eV and Egi = 2.27 eV at D = 0 Мrad to Egd = 2.35 eV and Egi = 2.32 eV at D = 25 Мrad for TlInS2 crystals. A decrease in the transmission coefficient at doses from 0 to 5 Mrad with a further increase in the transmission coefficient at a radiation dose of D = 25 Мrad is observed.
[en] Nano-dimension topologic-disorder materials constitute an important feature in the development of modern electronics. Among such materials, low-dimensional (1D and 2D) compounds, show amazing properties, for example highly anisotropic super ionic conductivity. Here it is shown that in the THz spectrum of such materials, which exhibit strong absorption lines that could be attributed to the libration oscillation of the nanofibers. In classical THz time-domain spectroscopy (THz-TDS), one records the temporal waveforms impinging onto and transmitted by the sample. Then a numerical FFT of both signals is performed. The ratio of the transmitted and incident FFT spectra gives the transmission coefficient of the sample. If the origin of time is preserved between the two requested measurements, then the FFT gives both modulus and phase of the transmission coefficient. If the sample is a slab with parallel sides, the index of refraction and the coefficient of absorption could be accurately determined using an inverse electromagnetic method. For materials exhibiting high absorption bands, the transmission coefficient is almost zero in modulus, and its phase is unknown. The usual solution to this problem is to perform THz-TDS in reflection. Here it is proposed a combined technique, which takes benefit of both transmission and reflection THz-TDS's. The basic idea is to derive a rough estimation of the refractive index from reflection data, while both refractive index and absorption coefficient are also calculated from transmission data. A Kramers-Kronig calculation allows to determine the refractive index from the absorption spectrum measured in transmission. In the spectral regions of transparency, both refractive indices determined from reflection and from the Kramers-Kronig calculation should be superimposed. The method had been applied to determine the index of refraction of low dimensional compounds. Refractive index (full circles) and absorption (dashed line) spectra of the crystal, showing strong absorption bands.
[en] Alloys in the TlSe-Se system on the side of the TlSe compound in the phase diagram have been investigated using differential thermal, X-ray powder diffraction, and microstructural analyses. The phase diagram of the system has been constructed, and the temperature dependences of the electrical conductivity of the phases obtained have been examined. An analysis of the thermograms of alloys in the (TlSe)0.96-Se0.04 system has revealed a structural phase transition at a temperature of 470 ± 1 K. Investigations into the temperature dependences of the electrical conductivity in the range 120-450 K have demonstrated that the temperature dependence of the electrical conductivity for the (TlSe)0.96-Se0.04 alloy exhibits metallic behavior.
[en] We report on the first NMR study of powder and single crystal samples of thallium indium sulfide, TlInS2. The crystal under study is a pure single-layer TlInS2 polytype. Our findings show that transformation from the high temperature paraelectric phase to the low temperature ferroelectric phase occurs via an incommensurate phase that exists in the temperature range from Tc = 192 K to Ti = 205 K. On approaching the phase transition at Ti from above, the crystal exhibits a soft mode behavior. A discrepancy in the literature data on the phase transitions in TlInS2 is discussed and ascribed to polytypism of the TlInS2 crystals. (paper)