The nature of anionic clusters in anion excess fluorite-type oxidefluoride solid solutions in MF–BiF3–BiOF systems (M = Na, K)

Various compositions of the range of fluorite-type oxidefluoride solid solution in the NaF-BiF3-BiOF system are investigated by 19F NMR spectroscopy. Using the following formulation, Na0.5(1−z−h)Bi0.5(1+z+h)F2+z−hOh, this study is undertaken as a function of the anion excess (z) and the oxygen content (h). It results in the existence of two fluoride sublattices in the solid solution range. An approach to the nature of the fluorine-oxygen order is proposed when the compositions become richer and richer in BiOF. The clustering model is then extended to the homologous potassium oxidefluoride solid solutions.