Multinuclear NMR studies of mixed Ca1-xSrxF2 crystals

The local environments of fluorine and calcium ions in Ca1-xSrxF2 single crystals have been studied using F-19 and Ca-43 magic-angle spinning (MAS) NMR spectroscopies. The fluorine speciation is found to depend on both the distribution of cations (Ca and Sr) around each fluorine site in the fluorite lattice, as well as fluctuations in the ionic character of bonding between fluorine and these cations. The natural abundance Ca-43 MAS NMR results show a clear relation between Ca-43 chemical shielding and bond distances in halides, with increasing shielding as the fluorite lattice expands and Ca-F distances lengthen. When taken together, the results from F-19 and Ca-43 NMR are consistent with a random substitution of Sr for Ca in the mixed fluoride system.