Within the Tl2O-Ag2O-TeO2 system, a large glass-forming domain was evidenced and is presented for the fist time. Densities, glass transition (T-g) and crystallization (T-c) temperatures of the relevant glasses were measured. A structural approach of these glasses as functions of the composition was performed using Raman scattering. The Raman spectra were analysed in terms of the structural modifications induced by the Tl2O and Ag2O modifiers. It has clearly evidenced a phase separation inherent in tellurite glasses with low valence cations (as Tl+ and Ag+). The glasses would be constituted of two phases only: one of pure TeO2 and one of pure ortho-tellurite M2TeO3 (M = Ag, Tl) with the statistically mixed Ag-Tl cationic composition. (C) 2010 Elsevier Ltd. All rights reserved.