Designed Y³⁺ Surface Segregation Increases Stability of Nanocrystalline Zinc Aluminate

The thermal stability of zinc aluminate nanoparticles is critical for their use as catalyst supports. In this study, we experimentally show that doping with 0.5 mol % Y₂O₃ improves the stability of zinc aluminate nanoparticles. The dopant spontaneously segregates to the nanoparticle surfaces in a phenomenon correlated with excess energy reduction and the hindering of coarsening. Y³⁺ was selected based on atomistic simulations on a 4 nm zinc aluminate nanoparticle singularly doped with elements of different ionic radii: Sc³⁺, In³⁺, Y³⁺, and Nd³⁺. The segregation energies were generally proportional to ionic radii, with Y³⁺ showing the highest potential for surface segregation. Direct measurements of surface thermodynamics confirmed the decreasing trend in surface energy from 0.99 for undoped to 0.85 J/m² for Y-doped nanoparticles. Diffusion coefficients calculated from coarsening curves for undoped and doped compositions at 850 °C were 4.8 × 10^-12 cm²/s and 2.5 × 10^-12 cm²/s, respectively, indicating the coarsening inhibition induced by Y³⁺ results from a combination of a reduced driving force (surface energy) and decreased atomic mobility.