The effect of K2O content on the crystallization of binary Teo(2)-K2O glasses was investigated. Glasses with compositions of (1 - x)TeO2-xK(2)O (where x=0.05, 0.10, 0.15, in molar ratio) were prepared. DTA curves in the temperature range of 25-700 degrees C with the heating rate of I 0 degrees C/min were used to determine the thermal properties such as glass transition temperature (T-g), crystallization peaks (T-p), and melting temperature (T-G). Crystallization peaks ranging between 364 and 421 degrees C were detected on the DTA scans. DTA results revealed that the most stable glasses were formed with the modifier concentrations near the eutectic composition, 0.10 mol. Crystallizing phases and microstructural morphology for each composition were characterized by XRD and SEM. On the basis of XRD measurements, alpha-TeO2 (paratellurite), - -(T)eo(2) and K2Te4O9 (potassium tetratellurite) phases were detected. The K2Te4O9 phase is present in all three glasses, due to the fact that this phase arises because of a phase separation melting of the glass. (c) 2006 Elsevier Ltd. All rights reserved.