Understanding Oxygen Ion Diffusion Mechanisms in YTiO3 Structures with Native Defects

Abstract

This study investigated the influence of native oxygen vacancies (V_O) and interstitial oxygen (O_i) defects on oxygen ion diffusion in YTiO₃. Using a combination of density functional theory (DFT) and molecular dynamics (MD) simulations, we explored the diffusion mechanisms and the role of these defects in enhancing ionic conductivity. Our results show that the presence of interstitial oxygen significantly promotes anisotropic diffusion of O^2– ions, with a strong preference for diffusion along the y-axis, a trend that persists across different temperatures and concentrations. This anisotropy is attributed to the distortions induced by interstitial oxygen atoms at the 8d Wyckoff positions, which weaken the bonds between oxygen atoms and the crystal lattice, facilitating diffusion. The analysis of residence times revealed that oxygen atoms at the 8d sites exhibit shorter residence times compared with those at the 4c sites, especially at lower temperatures. This behavior is explained by the higher probability of a vacancy occurring in the vicinity of the 8d sites, leading to a higher probability of oxygen migration from these positions. Overall, our findings provide valuable insights into the mechanisms governing oxygen ion diffusion in YTiO₃ and highlight the importance of interstitial oxygen defects in enhancing ionic conductivity, which could contribute to developing new cathode materials for solid oxide fuel cells (SOFCs).