204Tl tracer diffusion and conductivity in thallium thiogermanate glasses

Conductivity and 204Tl tracer diffusion measurements have been carried out in the (Tl2S)x(GeS)60(GeS2)40 − x glassy system, where the Tl2S concentration changes between 0 ≤ x ≤ 25. The room temperature dc conductivity increases by 7 orders of magnitude with increasing thallium concentration, ranging between 10− 18 S cm− 1 for the 60GeS-40GeS2 matrix and 10− 11 S cm− 1 for Tl2S-rich glasses. The activation energy decreases from 1.22 to 0.79 eV, respectively. The conductivity and thallium diffusion results reveal that the ionic transport becomes to be predominant at high thallium concentrations (≈ 15 at.% Tl). The thallium ion transport number tTl+ increases from 10− 3 for low cation concentrations to tTl+≅1 for the x = 20 sample. The Haven ratio, HR ≈ 1, indicates uncorrelated ion motion even at rather high thallium concentrations. The obtained results are discussed in comparison with similar (Ag2S)x(GeS)60(GeS2)40 − x glassy system.