Mixed cation effect in Ag2S–Tl2S–GeS–GeS2 glasses: Conductivity and tracer diffusion studies

Abstract Mixed cation effect has been studied for thallium–silver thiogermanate glasses in the (Ag 2 S) x (Tl 2 S) 50 -x (GeS) 25 (GeS 2 ) 25 system, where Ag 2 S fraction r  = Ag 2 S / (Ag 2 S + Tl 2 S) = 0, 0.25, 0.5, 0.75, and 1.0. The glass transition temperature changes from 160 °C for r  = 0 to 231 °C for r  = 1.0 and exhibits a negative deviation from additivity, with a slight minimum T g  ≈ 157 °C observed for compositions in the range 0.1 ≤  r  ≤ 0.3. The room temperature conductivity σ 298 increases by 5 orders of magnitude with increasing silver concentration, ranging between 10 − 8  S cm − 1 for the Tl–Ge–S system and 10 − 3  S cm − 1 for the Ag–Ge–S glass with a minimum at σ 298  ≈ 10 − 9  S cm − 1 . The activation energy decreases from 0.66 to 0.33 eV, respectively, with the maximum at E σ  ≈ 0.69 eV. The minimum of both T g and σ 298 and the E σ maximum are observed in the same composition range, 0.1 ≤  r  ≤ 0.3. The 204 Tl tracer diffusion coefficient at 170 °C decreases with silver concentration from 10 − 10  cm 2  s − 1 for (Tl 2 S) 50 (GeS) 25 (GeS 2 ) 25 glass to 10 − 12  cm 2  s − 1 for (Ag 2 S) 50 (GeS) 25 (GeS 2 ) 25 glass. The obtained results indicate a classical mixed cation effect.