Frequency dispersion of dielectric coefficients of layered TlGaS2 single crystals

Frequency dependence of the dissipation factor tanδ, the permittivity ?, and the ac conductivity σ_ac across the layers in the frequency range f=5×10⁴?3×10⁷ Hz was studied in layered TlGaS₂ single crystals. A significant dispersion in tanδ was observed in the frequency range 10⁶?3×10⁷ Hz. In the range of frequencies studied, the permittivity of TlGaS₂ samples varied from 26 to 30. In the frequency range 5×10⁴?10⁶ Hz, the ac conductivity obeyed the f^0.8 law, whereas for f>10⁶ Hz σ_ac was proportional to f². It was established that the mechanism of the ac charge transport across the layers in TlGaS₂ single crystals in the frequency range 5×10⁴?10⁶ Hz is hopping over localized states near the Fermi level. Estimations yielded the following values of the parameters: the density of states at the Fermi level N_F=2.1×10¹⁸ eV^?1 cm^?3, the average time of charge carrier hopping between localized states τ=2 µs, and the average hopping distance R=103 Å.