Influence of Morphology of LaF 3 Nano-crystals on Fluorine Dynamics Studied by NMR Diffusometry

Ionic dynamics in nano-structured 2D superionic conductors LaF3 obtained by a synthesis at the gas–solution interface has been analyzed using 19F NMR Static Field Gradient (SFG) diffusometry in a temperature range up to 800 K. The fluorine diffusion in 2D materials is significantly higher as compared to that in bulk LaF3 and is strongly dependent on the nano-crystalline sheet thickness. Its decrease from 18 nm to 6 nm leads to an increase of mobility by almost two orders of magnitude, resulting in an overall mobility enhancement of more than three orders of magnitude compared to mono-crystalline LaF3. Moreover, the activation energy is reduced from 1.2 eV for mono-crystals to 0.23 eV for 6 nm thin nano-crystalline powder samples.