Dependencies of the lattice parameters and the coefficient of thermal expansion of TlInTe2 crystals on temperature are studied at a wide range of temperatures by using XRD, dilatometer, differential thermal analysis, and impedance spectroscopy (IS) methods. The IS measurements of the dielectric function were done along the c-axis and normal to the (110)-plane. IS for E ⊥ (110)-plane was done for two values of the amplitudes, U0 = 0.04 V and 1 V, of ac-voltage with different frequencies; moreover, the measurements for E∥c were realized at U0 = 0.04 V only. IS measurements demonstrate a sequence of the phase transitions (PTs) to the ferroelectric and the ionic conductivity states, also to a structural phase transition. Tl+ ions are shown to shift in the direction of normal to c-axis in the ferroelectric PT, but they are activated along the c-axis in the ionic conductivity PT. The dielectric function in the ionic conductivity PT is shown to increase to a huge positive value and then to drop to a big negative value, reversing its sign. An explanation of this effect is provided as a competition of Drude and polarization contribution to the dielectric function under ac-electric field. Thermal effects of the phase transitions were determined.

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-Temperature dependences of electrical conductivity (T), switching effect, THz spectra and permittivity ε(T) of onedimensional (1D)TlGaTe2

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The temperature dependences of the conductivity and permittivity of the Ag8GeSe6 compound have been studied in direct and alternating electric fields. This phenomenon is associated with the process of charge accumulation at the boundary of the sample with ionic conductivity and the blocking electrode, and the formation of a double electric layer. The observed dielectric relaxation is associated with the transition of the crystal to the superionic state. It has been established that hopping conduction with a variable hopping length over localized states near the Fermi level takes place in an Ag8GeSe6 crystal.