Аннотация:Exsolution of excess transition metal cations from a non-stoichiometric perovskite oxide has sparked interest as a facile route for the formation of stable nanoparticles on the oxide surface. However, the atomic-scale mechanism ofthis nanoparticle formation remains largely unknown. The present in situ scanning transmission electron microscopy combined with density functional theory calculation revealed that the anti-phase boundaries (APBs) characterizedby the a/2 <011> type lattice displacement accommodate the excess B-site cation (Ni) through the edge-sharing of BO6 octahedra in a nonstoichiometric ABO3 perovskite oxide (La0.2Sr0.7Ni0.1Ti0.9O3-δ) andprovide thefast diffusion pathways for nanoparticle formation by exsolution. Moreover, the APBs further promote the outward diffusion of the excess Ni toward thesurface as the segregation energy of Ni is lower at the APB/surface intersection. The formation of nanoparticles occurs through the two-step crystallization mechanism, i.e., the nucleation of an amorphous phase followed by crystallization,and via reactive wetting on the oxide support, which facilitates the formation of a stable triple junction and coherent interface, leading to thedistinct socketing of nanoparticles to the oxide support. The atomic-scale mechanism unveiled in this study can provide insights into the design of highly stable nanostructures.