Dielectric Properties and Electrical Conductivity of (_1–x)TlGaSe₂ · xTm Crystals

We have synthesized samples based on the layered compound TlGaSe₂ and containing thulium: (1–x)TlGaSe₂ · xTm with x = 0.001, 0.005, 0.01, and 0.02. The polycrystalline samples have been used as charges for growing crystals with the corresponding compositions by the Bridgman method. The phase composition of the (1–x)TlGaSe₂ · xTm samples has been determined by X-ray diffraction analysis. Their dielectric properties have been studied in ac electric fields at frequencies in the range f = 5 × 10⁴ to 3.5 × 10⁷ Hz. We have identified the relaxation character of the dielectric permittivity, the nature of the dielectric loss, and the hopping mechanism of charge transport in the (1–x)TlGaSe₂ · xTm crystals. Our results demonstrate that increasing the thulium concentration in the crystals reduces the mean hop distance and time of charge carriers and increases the ac conductivity and the density of localized states near the Fermi level in the crystals.