The influence of Li2O on the structural and thermal properties of Al2O3–CaO–K2O–Na2O–SiO2 glass

Abstract This study investigates and compares the structural and thermal properties of six glasses in the Al 2 O 3 –CaO–K 2 O–Li 2 O–Na 2 O–SiO 2 system with varying Li 2 O concentration (0–10 mass%). The physicochemical, thermal, and structural characteristics were systematically analyzed. The addition of Li 2 O resulted in a change in glass density ranging from 2.50 to 2.53 g cm -3 and in a decrease of the molar volume (from 61 to 56 cm 3 mol -1 ), attributed to the formation of non-bridging oxygens (NBO) and a more compact glass structure. X-ray diffraction confirmed that samples up to 6 mass% Li 2 O remained fully amorphous. Differential thermal analysis revealed a decrease in glass transition temperature ( T g ) with increasing Li 2 O content and the appearance of exothermic crystallization peaks between 600 and 800 °C for glasses containing 8–10 mass% Li 2 O. Raman spectroscopy confirmed that Li 2 O acts as a network modifier, breaking Si–O–Si linkages and increasing the intensity of the band at 960 cm −1 , corresponding to Si–O stretching vibrations. The study also highlighted the changes in Q n structural units with increasing Li 2 O concentration, leading to enhanced depolymerization and structural distortion of the silicate network.