Ni diffusion in ceria lattice: A combined experimental and theoretical study

Abstract

Cation diffusion in ceria is of significant importance in many fundamental processes, but the mechanism by which 3d-transition metals migrate in ceria has not yet been elucidated. Here, we select Ni as a representative transition metal and combine experimental and theoretical analyses to determine where Ni is located in ceria and how it migrates. Bulk Ce0.995Sm0.005O1.9975-δ pellets are prepared with a sputtered NiO source on top, and the diffusion coefficient of the Ni impurity is measured at temperatures from 1250 to 1350 °C by analyzing the depth profiles of Ni via time-of-flight secondary ion mass spectrometry. In addition, corresponding activation enthalpy values for Ni diffusion when Ni is present in substitutional and interstitial sites are calculated by density functional theory and compared with the measured values. We reveal that the diffusion of Ni impurity mainly occurs via the interstitial mechanism in ceria and propose an atomic-scale interpretation of Ni migration.