Morphological and dynamical evolution of lanthanum fluoride 2D nanocrystals at thermal treatment

Abstract A detailed study of the morphological evolution of 2-dimensional LaF3 nanocrystals under the thermal treatment in air was performed. XRD, SEM, TEM and 19F MAS NMR techniques were used to characterize the aggregation process of nanocrystals. 19F NMR relaxometry and diffusometry were applied to investigate changes in the dynamics of the fluorine ions. Heating of nano-structured LaF3 above 800 K led to crystallite growth accompanied by a deceleration of ionic motion, as seen from the NMR relaxation and diffusion data. The effect is dependent on the annealing temperature, and its enhancement above 1000 K causes the morphology and dynamics of the 2D nanocrystals to approach that of the bulk material. 19F MAS NMR confirms that the local structure of annealed 2D LaF3 is identical to that of the bulk material.