Probing the ionic structure of FLiNaK-ZrF 4 salt mixtures by solid-state NMR.

In this study, by applying 19 F, 23 Na and 7 Li high-resolution NMR methods, the evolution of the [Zr x F y ] 4 x - y local ionic structures in FLiNaK-ZrF 4 salt mixtures were elucidated. K 3 ZrF 7 , Na 3 ZrF 7 and Na 7 Zr 6 F 31 crystal phases were identified when the melt salts were being solidified. The distribution of these [Zr x F y ] 4 x - y species was dependent on the content of ZrF 4 in FLiNaK eutectic salts. Moreover, K 3 ZrF 7 phase transition from an orthorhombic lattice into a disordered cubic lattice was clarified, thereby causing dynamics of the coordinated F - ions to be reduced and the well-ordered crystal lattices to be destroyed. These mentioned results provide a further insight into the Zr-F based ionic structure and the formation of the disordered Zr-F structure in ZrF 4 -based eutectic salts.