Ion conductivity of TlSe₁-xS_x (x = 0.1) solid solutions irradiated with γ quanta by the method of impedance spectroscopy

The frequency dependences of permittivity of TlSe₁-xS_x (x=0; 0.1; 0.2) solid solutions, unirradiated and irradiated at 0.1 MGy at the temperature range of 100-450 K and frequency range of 25-106 Hz and real and imaginary parts of impedance were studied by impedance spectroscopy. The obtained complex plane diagrams were analyzed using the method of equivalent circuit substitutions. It has been shown that in TlSe₁-xS_x (x=0; 0.1; 0.2) solid solutions, the phase transition to the superionic state under the influence of γ irradiation occurs at lower temperatures. TlS and TlSe monocrystals formed by TlSe₁-xS_x (x=0-1.0) system solid solutions belong to the class of A3B6 type semiconductor compounds and crystallize in chain (tetragonal) modification. The TlS single crystal crystallizes in isostructure and tetragonal symmetry with TlSe. In this work, a capacitor was made from the studied materials to measure the temperature dependence of the electrical conductivity of TlSe₁-xS_x (x=0.1) solid solution samples grown by the Bridgeman method. Measurements were made with the E7-25 digital immitas measuring device. In the presented work, the complex impedance and relaxation processes of TlSe₁-xS_x (x=0; 0.1; 0.2) solid solutions, unirradiated and irradiated with gamma quanta, were investigated. The real and imaginary parts of the impedance of TlSe₁-xS_x (x=0; 0.1; 0.2) solid solution samples irradiated at 0 and 0.1MGy doses were measured. Based on the experimental results, a complex impedance godograph is described. It was determined that the arc of the complex plane godograph for solid solution samples before irradiation describes a curve inclined to the real axis close to maximum semicircle at the point of intersection of Z1 and Z2. This form of dependence corresponds to the parallel equivalent substitution scheme. In this case, the energy transport is characterized by a single relaxation time. Thus, an increase in the frequency f₍max) corresponding to the maximum of Z2 in the solid solution is observed. In the measurements performed before irradiation, the fact that the real axis has a shape close to a semicircle located in the center was associated with the characterization of the charge transport process by a single relaxation time. This type of godograph corresponds to a homogeneous sample with low resistance and non- isolating contact. The diagrams in the (Z2-Z1) complex plane obtained from the measurements after irradiation at a dose of 0.1 MGy were semicircular for a parallel RC-chain, reflected by ^rays in the low-frequency region of the diagrams. The godograph curves of the (Z2-Z1) complex impedance obtained after 0.1 MGy irradiation show that there are additional effects on conductivity due to the diffusion transport of thallium ions near the solid electrolyte and electrode boundary. These rays in the impedance diagram are, in our opinion, related to Warburg's diffusion impedance. Warburg diffusion impedance is based on the fact that the sinusoidal signal of given diffusion carriers cannot reach the boundary of the diffusion layer in the frequency range. The formation of Warburg's diffusion impedance is considered to be the diffusion of Tl+1 ions observed after γirradiation with the transition of the crystal into a superionic state.