Compositional effects on the structure and properties of CaO-Al2O3-Ga2O3 glasses

In this work, we investigated the structural and physical property evolutions induced by the substitution of Al₂O₃ by Ga₂O₃ in two series of CaO-Al₂O₃-Ga₂O₃ (CAG) glasses. To suppress crystallization, glasses with compositions of (I) 50CaO• (50-x)Al₂O₃• xGa₂O₃ (x = 0–50 mol%) and (II) 63CaO• (37-x)Al₂O₃• xGa₂O₃ (x = 0–37 mol%) were prepared via containerless aerodynamic levitation technique. It was found that with increasing substitution of Al₂O₃ by Ga₂O₃ (i.e., increasing x), both glass series exhibited monotonic decreases in hardness, glass transition temperature and thermal expansion coefficient. High-resolution XPS analyses revealed that the two glass series exhibited distinct compositional dependences in their local structural evolution. Specifically, in series I ([CaO]:[Al₂O₃+Ga₂O₃] = 1:1), the coordination environments of O, Ga, and Al remained largely unchanged upon substitution. In contrast, Series II ([CaO]:[Al₂O₃+Ga₂O₃] = 12:7) exhibited significant shifts in O and Al coordination, while the Ga environment was only minimally affected. Furthermore, XPS indicated that trace OH^- species preferentially interact with Al/Ga-O bonds by non-bridging oxygens within [AlO₄] or [GaO₄] tetrahedra. These findings elucidate the critical roles of both [CaO]/[Al₂O₃+Ga₂O₃] and [Al₂O₃]/[Al₂O₃+Ga₂O₃] ratios in tailoring the structure - property relationships of CAG glasses.