Size Reducing Rupture during “Growth” of LnF3 (Ln = La, Lu, Y) Nanocrystals Due to Cogeneration of Structure and Stress

Abstract

Crystal growth involves an increase in the average size of crystals even during Ostwald ripening, wherein larger crystals grow at the expense of smaller crystals. In contrast, we observed particle size reduction due to rupture during the growth of polycrystalline LnF3 (Ln = Lu, Y, La) nanoparticles. We rationalize this by the feature of the growing crystal to evolve toward the most stable native crystal form via several metastable intermediate non-native amorphous or crystalline structures with a significant change in density, resulting in high misfit strain and generation of stress within the single nanoparticle. The stress promotes the propagation of already existing flaws in the crystal, leading to the rupture of nanocrystals and a subsequent decrease in crystallite size. Results from finite element elastic simulations also support the propagation of flaws leading to nanocrystal rupture if the fracture toughness of the materials is low. The ligand plays an essential role in the observation of this phase of crystal growth by retarding the growth kinetics.