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[en] Samples of (TIGaSe2)1-x(TIInSe2)x solid solutions are synthesized. The frequency dependences (2*10''1-10''6 Hz) of components of the total complex impedance are studied by the impedance spectroscopy technique and relaxation processes are investigated depending on the composition of the (TIGaSe2)1-x(TIInSe2)x solid solution in the solubility region (x=0-0.3). Corresponding diagrams on the (Z-Z') complex plane are analyzed using the equivalent substitution circuit method. An anomaly in the temperature dependence of the electrical conductivity, which manifests itself in an abrupt increase in the conductivity, is found for the studied (TIGaSe2)1-x (TIInSe2)x solid solution at 300K. This peculiarity is associated with the phase transition into the superionic state after 0.25 MGy gamma irradiation.
[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] 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] Temperature dependences of electrical conductivity σ(T) and current-voltage characteristics of one-dimensional TlGaTe2 single crystals subjected to various doses of γ-ray radiation in both geometries of the experiment-along nanochains parallel to the tetragonal axis of the crystal (σ| ) and perpendicular to these nanochains (σperpendicular )-are studied. It is shown that the dependence σ(T) measured in the ohmic region of the current-voltage characteristic is the shape typical of the hopping mechanism and can be described in terms of the Mott approximation. The values of the densities of localized states NF, the activation energy Ea, the hop lengths R, the difference between the energies of states ΔE in the vicinity of the Fermi level, and the concentrations of deep traps Nt are determined. The current-voltage characteristics in the region of a more abrupt increase in the current are also studied. It is shown that this region of current-voltage characteristics is described in the context of the Pool-Frenkel thermal-field effect. Concentrations of ionized centers Nf, the free-path lengths λ, the Frenkel coefficients β, and the shape of the potential well in initial and irradiated (with 250 Mrad) TlGaTe2 crystals are determined. It is shown that anisotropy of electrical conductivity changes under the effect of irradiation, which brings about translational ordering of nanochains.
[en] The switching effect, field and temperature dependences of the permittivity and conductivity of TlGaTe2 crystals subjected to various γ-irradiation doses are studied. Under rather low electric fields, the phenomenon of threshold switching with an S-shaped current-voltage characteristic containing a portion with negative differential resistance is observed in the crystals. In the region of critical voltages, current and voltage oscillations and imposed modulation are observed. Possible mechanisms of switching, ionic conductivity, disorder, and electrical instability in TlGaTe2 crystals are discussed.