The xGa₂O₃–(100 − x)NaPO₃ glass system: Preparation, properties and structural analysis by solid state NMR

Insertion of Ga₂O₃ in sodium metaphosphate glasses has been investigated in this paper. Materials containing up to 30 mol% of Ga₂O₃ have been prepared using the standard melt-quenching technique within the xGa₂O₃–(100 − x)NaPO₃ composition line. Macroscopic properties (glass transition temperature, density and molar volume) are significantly affected by the Ga₂O₃ insertion. 1D ⁷¹Ga and ³¹P magic angle spinning nuclear magnetic resonance (MAS-NMR) performed at very high field (18.8 T) indicate a strong evolution of the gallium coordination state around the x = 15 composition and a continuous evolution of the phosphate network organisation. In addition, ⁷¹Ga(³¹P) D-HMQC NMR technique was used for the first time to highlight the presence of mixed P–O–Ga linkages within the glass structure. The impact of gallium insertion is finally discussed and compared to the effect of the widely used aluminum and boron elements. If gallium and aluminum elements present similar effect on the macroscopic properties, some discrepancies can be observed concerning their structural effect. - Highlights: • Glasses with 30 mol% of Ga₂O₃ have been prepared in the NaPO₃–Ga₂O₃ line. • T_g and density are affected by the Ga³⁺ insertion. • Presence of mixed Ga/P species have been highlighted by 2D correlation NMR