The new salt heating magic-angle spin (MAS) system for high-temperature nuclear magnetic resonance (HT-NMR) is achieved by a laser heating beam coupled with optical fiber. The formation of a sodium ion-doped crystal KF phase is revealed in FLiNaK ternary eutectic salt (46.5%LiF–11.5%NaF–42.0%KF), which is considered unable to exist at room temperature according to its phase diagram. Density functional theory (DFT) simulation proved that Na+ ion-doped crystal is clearly ascertained to develop with the solidification of the melt. Temperature dependence, relaxation, and variable contact time cross-polarization NMR studies provide insights into the unique dynamics and the spatial scale of the doped Na+ ions in KF crystals, which exhibit faster ionic vibration due to the weakening of coordinated interactions from the ambient F– ions.

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The evolution of the [ZrxFy]4x−y ionic structures in FLiNaK–ZrF4 salt mixtures was elucidated through solid-state NMR techniques when the melt salts were being solidified.