INVESTIGATION OF FLUORINE OCTAHEDRON CONNECTIVITIES IN TRANSITION-METAL FLUORIDE GLASSES BY SOLID-STATE F-19 MAGIC-ANGLE-SPINNING NUCLEAR-MAGNETIC-RESONANCE SPECTROSCOPY

High-resolution magic-angle-spinning (MAS) F-19 NMR spectroscopy is us ed to investigate the structural properties of some transition metal f luoride glasses (PbF2-ZnF2-GaF3) related to the fluorine network. Seve ral glass compositions are investigated in order to vary the PbF2/ZnF2 /GaF3 ratios. F-19 MAS NMR experiments are carried out on certain crys talline compounds selected as being the initial constituents (PbF2ZnF2 ,GaF3) or recrystallization compounds (Pb2ZnF6, PbGaF5, Pb3Ga2F12, Pb9 Ga2F24) of glassy phases, or because they have some specific particula r connectivities of the fluorine octahedron network (e.g. CsZnGaF6). I t is shown that three types of fluorine are involved in the glass netw ork: free fluorines which are not connected to transition metal ions, and shared and unshared fluorines belonging to (ZnF6)(4-) and (GaF6)(3 -) octahedra. Quantitative information on these three different fluori ne sites, their relative ratios in the glassy networks, and the degree of cross-linking of the fluorine octahedra is obtained. Our results p rove the validity of the previously adopted assumption according to wh ich the glass network is built up from corner-sharing fluorine octahed ra centred on transition metal ions.