Accelerating metal nanoparticle exsolution by exploiting tolerance factor of perovskite stannate

Abstract

The octahedral symmetry in ionic crystals can play a critical role in atomic nucleation and migration during solid–solid phase transformation. Similarly, octahedron distortion, which is characterized by Goldschmidt tolerance factor, strongly influences the exsolution kinetics in the perovskite lattice framework during high-temperature annealing. However, a fundamental study on manipulating the exsolution process by octahedron distortion is still lacking. In this study, we accelerate Ni metal exsolution on the surface of perovskite stannates by increasing the [BO₆] octahedron distortion in the lattices. Decreasing the A-site ionic radius (r_Ba²⁺ = 161 pm → r_Sr²⁺ = 144 pm → r_Ca²⁺ = 134 pm) increased the density of exsolved Ni nanoparticles by up to 640% (i.e., 47 particles μm⁻² of Ba(Sn, Ni)O₃ → 304 particles μm⁻² of Ca(Sn, Ni)O₃) after the identical exsolution process. Based on the theoretical calculation and experimental characterization, the decrease in crystal symmetry by octahedral distortion promoted the Ni exsolution owing to the boosted Ni migration by weakening the bond strength and generating domain boundaries. The findings highlight the importance of octahedral distortion to control atomic migration through the perovskite lattice framework and provide a strategy to tailor the density of uniformly populated nanoparticles in nanocomposite oxides for multifunctional material design.