Probing the ionic structure of FLiNaK-ZrF4 salt mixtures by solid-state NMR

In this study, by applying F-19, Na-23 and Li-7 high-resolution NMR methods, the evolution of the [ZrxFy](4x-y) local ionic structures in FLiNaK-ZrF4 salt mixtures were elucidated. K3ZrF7, Na3ZrF7 and Na7Zr6F31 crystal phases were identified when the melt salts were being solidified. The distribution of these [ZrxFy](4x-y) species was dependent on the content of ZrF4 in FLiNaK eutectic salts. Moreover, K3ZrF7 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 ZrF4-based eutectic salts.

Automated summary

By applying high-resolution NMR methods, this study elucidated the evolution of [ZrxFy](4x-y) local ionic structures in FLiNaK-ZrF4 salt mixtures, revealing the impact of ZrF4 content on the distribution of these species. The phase transition of K3ZrF7 from an orthorhombic lattice to a disordered cubic lattice was clarified, highlighting the influence of lattice changes on the dynamics of F- ions and crystal structure.