Composition-dependent evolution toward multi-phase crystallization in lanthanum tellurite glasses

Tellurite-based glass systems have attracted considerable attention owing to their promising thermal and optical characteristics for advanced glass and glass-ceramic applications. The present study investigates the influence of La 2 O 3 addition on the thermal behavior, crystallization kinetics, and phase evolution of TeO 2 -based binary glasses. TeO 2 -La 2 O 3 samples containing 5–30 mol% La 2 O 3 were synthesized via melt quenching and characterized using physical, structural, and non-isothermal DSC analyses. XRD results confirmed that the predominantly amorphous character was retained up to 20 mol% La 2 O 3 , whereas 30 mol% La 2 O 3 content promoted crystallization and the formation of lanthanum-rich crystalline phases. Increasing La 2 O 3 content increased glass density from 5.22 to 5.51 g.cm -3 and T g from 640 to 741 K, while simultaneously decreasing the glass stability parameter ΔT from 37 to 25 K. Non-isothermal kinetic analyses suggested a composition-dependent evolution in crystallization behavior. The low-La composition (95T5L) exhibited relatively sequential crystallization characteristics, whereas the high-La formulation (80T20L) showed evidence of a more complex phase assemblage after heat treatment at the first crystallization-peak temperature. Comparison of the representative low- and high-La compositions demonstrated a substantial increase in E p1 from approximately 192–194 to 348–353 kJ.mol -1 , accompanied by a decrease in E p2 from approximately 261–274 to 220–235 kJ.mol -1 with increasing 5 and 20 mol% La 2 O 3 content, respectively. This suggested the redistribution of the apparent activation energies associated with the crystallization events. Post-heat-treatment XRD analyses were consistent with the kinetic findings by revealing the coexistence of multiple La-rich crystalline phases in the heat-treated high-La composition. In conclusion, the present results suggest that increasing La 2 O 3 content is associated with a composition-dependent evolution from relatively sequential crystallization toward increasingly complex crystallization behavior. These findings provide useful insight into crystallization control and composition-dependent phase evolution in tellurite-based glass and glass-ceramic systems and establish a scientific basis for future studies of their thermal processing and potential optical and photonic applications.