19F high speed MAS NMR investigation of AlF63- octahedron connectivity in fluoroaluminate glasses

19F high speed MAS NMR spectra were recorded for 13 glass compositions with different CaF2/BaF2/AlF3 contents. The reconstruction of these spectra evidences three different contributions whose isotropic chemical shifts δiso and relative intensities were determined. Assuming AlF63- octahedron network for these glasses, the analysis of the δiso values was carried out in the light of the δiso ranges previously determined for crystallized compounds from the CaF2–AlF3, BaF2–AlF3 and BaF2–CaF2–AlF3 systems, and according to the constraints issued from the glass compositions. The parameter β giving the mean number of fluorine atoms per octahedron was then determined for each investigated glass. This parameter decreases from 6 to 5 when the AlF3 glass content increases from 35% to 50%, which corresponds to low octahedron network connectivities, comprised between 0D (isolated octahedra) and 1D (infinite chains of octahedra).