Properties and structural investigation of gallophosphate glasses by 71 Ga and 31 P nuclear magnetic resonance and vibrational spectroscopies

The structure and optical properties of new gallophosphate glasses in the pseudo-binary system x Ga 2 O 3 − (100 − x ) NaPO 3 ( x = 0 to 30 mol%), have been investigated. The effect of the progressive addition of Ga 2 O 3 on the local glass structure has been evaluated using Raman and infrared spectroscopies, and 71 Ga and 31 P magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. 71 Ga MAS NMR spectra collected at ultrahigh magnetic field (21.1 T) and fast spinning rates (60 kHz) permit the quantification of gallium in 4-, 5- and 6-fold coordination as a function of the Ga 2 O 3 concentration. At low concentrations of Ga 2 O 3 , high-coordinate gallium coordinates to oxygens associated with the phosphate chains, increasing the dimensionality and strengthening the glassy network. At moderate Ga loadings, tetrahedral Ga is incorporated into the phosphate chains, introducing additional branching sites which further enhances network connectivity. Higher Ga 2 O 3 content results in the formation of Ga–O–Ga bonds, thereby inhibiting glass formation. 31 P MAS NMR and Raman and infrared spectroscopies provide complementary information about the distribution and connectivity of the phosphate groups within the glass network, supporting a structural model which is correlated with the measured optical and thermal properties of the Ga 2 O 3 –NaPO 3 glasses as a function of the Ga 2 O 3 concentration.