Effect of alkaline earth oxides on ceramization of LaF3 in aluminosilicate glass: 19F MAS-NMR study

Local environment of fluorine atoms in the lanthanum oxyfluoride aluminosilicate glasses and glass-ceramics modified by alkaline earth oxides, i.e. MgO, CaO and BaO, was studied by solid state 19F MAS-NMR spectroscopy. The effect of the type and concentration of the modifier on the formation of crystalline LaF3 phase was determined, as a function of heat treatment conditions. In all series of glasses studied, the F–Me(n), but no Na–F species were observed. The presence of F–La,Ba(n) units, in which fluorine is coordinated both by lanthanum and barium, was detected in the Ba-glass. Supplementary XRD analysis of this series confirmed that an increase of barium contents leads to the formation of Ba0.3La0.7O0.7F1.3, instead of pure LaF3 only.