Superionic Conductivity and Specific Effects Induced by γ-Radiation in Nanofibrous TlGaTe2 Crystals

Abstract

Temperature dependences of electrical conductivity (T), switching effect, THz spectra and permittivity e(T) of onedimensional (1D) TlGaTe2 single crystals are investigated. The superionic conductivity observed at temperatures above 305 K is related to diffusion of Tl+ ions via vacancies in the thallium sublattice between   2 2 3 Te Ga nanochains. A relaxation character of dielectric anomalies suggests the existence of electric charges weakly bound to the crystal lattice. Upon the transition to the superionic state, relaxors in the TlGaTe2 crystals are Tl+ dipoles ((   2 2 3 Te Ga ) nanochains) that arise due to melting of the thallium sublattice and hops of Tl+ ions from one localized state to another. The effect of a fieldinduced transition of the TlGaTe2 crystal to the superionic state is detected. The temperature dependences of σ(T) and currentvoltage characteristics subjected to various doses of γradiation in both geometries of the experiment, along nanochains parallel to the tetragonal axis of the crystal σ) and perpendicular to these nanochains, 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. The current-voltage characteristics in the region of a more abrupt increase in the current are also studied and explained in the context of the Pool-Frenkel thermal-field effect. It is shown that anisotropy of electrical conductivity changes under the effect of irradiation, which brings about translational ordering of nanochains. Terahertz time-domain spectroscopy reveals absorption lines at approximately 0.2 THz that may be attributed to the libration oscillations of the nanofibers in the superionic phase.