Tl+ ion Conducting Glasses in the Tl-Ge-S System

Tl+ ion conducting glasses in the (Tl2S)x(GeS)50-x/2(GeS2)50-x/2 system, where Tl2S concentration changes between 0 ≤ x ≤ 50, were analysed. The glass transition temperature decreases significantly with increasing x from 358 °C (x = 0) to 160 °C (x = 50), indicating a strong depolymerisation of germanium-sulphur network. Raman spectroscopy studies confirm this conclusion, reflected by changes in corner- and edge-sharing GeS4 tetrahedra, GeS4-nGen tetrahedral units having Ge-Ge bonds at ≈ 2.45 Å, and the appearance of non-bridging sulphur species. 204Tl tracer diffusion, dc conductivity and ac impedance measurements have been used to study ionic and total conductivity in the glasses. The glasses belong to ionic conductors and their conductivity increases drastically with increasing thallium concentration, ranging between 10-17 S cm-1 for the 50GeS-50GeS2 matrix and 10-8 S cm-1 for Tl2S-rich glasses at 298 K, the activation energy decreases from 1.11 to 0.63 eV, respectively.