Solid Solutions CaF₂–YF₃ with Fluorite Structure Prepared on the Sol–Gel Route: Investigation by Multinuclear MAS NMR Spectroscopy

Nanoscaled Ca_1–<i>x</i>Y_<i>x</i>F_2+<i>x</i> (<i>x</i> = 0...0.40) was prepared on the new fluorolytic sol–gel route using organic precursors and anhydrous HF. These nonstoichiometric fluorite-type phases were investigated using ¹⁹F MAS and ¹⁹F–⁸⁹Y CP MAS NMR. Excess fluoride ions occur as point defects for <i>x</i> ≤ 0.01. For <i>x</i> > 0.01 excess fluoride ions start clustering. The ¹⁹F spectra of these phases can be fully explained by assuming a distribution of Ca²⁺ and Y³⁺ around fluoride ions. Y³⁺ is distributed within the crystal lattice of CaF₂, with higher concentrations near fluoride clusters. Two different coordination polyhedra for Y³⁺ are observed. The correlation between ¹⁹F and ⁸⁹Y signals was established