Coulomb interaction enabled slow oxygen diffusion within grain boundaries in yttria-stabilized zirconia

Oxygen diffusion within grain boundaries (GBs) is expected to be fast due to the disordered, open structure of the boundary region. Here, we report suppressed oxygen diffusion within GB regions in yttria-stabilized zirconia (YSZ) and relate this slowdown to Coulomb interactions between ionic defects. Using molecular dynamics simulations, we identify anion–cation coordination deficiencies at GBs. Single-crystal simulations with controlled Zr4+ vacancy concentrations reveal that oxygen mobility decreases exponentially with increasing Zr4+ vacancy density. In these single-crystal models, the slow oxygen diffusion originates from electrostatic attraction between negatively charged Zr4+ vacancies and surrounding oxygen vacancies, forming stable anion–cation vacancy complexes that trap oxygen vacancies and hinder their migration. The distribution of oxygen vacancies around different defects further supports this Coulomb trapping mechanism. Our findings provide insight into the counterintuitive observation of slow GB oxygen diffusion in YSZ and provide a new, defect-interaction-based perspective for designing YSZ in high-temperature oxidation-resistant applications.