A Computational Study of Yttria-Stabilized Zirconia: II. Cation Diffusion

摘要

Cubic yttria-stabilized zirconia is widely used in industrial electrochemicaldevices. While its fast oxygen ion diffusion is well understood, why cationdiffusion is much slower-its activation energy (~5 eV) is 10 times that ofanion diffusion-remains a mystery. Indeed, all previous computational studiespredicted more than 5 eV is needed for forming a cation defect, and another 5eV for moving one. In contrast, our ab initio calculations have correctlypredicted the experimentally observed cation diffusivity. We found Schottkypairs are the dominant defects that provide cation vacancies, and their localenvironments and migrating path are dictated by packing preferences. As acation exchanges position with a neighboring vacancy, it passes by an emptyinterstitial site and severely displaces two oxygen neighbors with shortenedZr-O distances. This causes a short-range repulsion against the migratingcation and a long-range disturbance of the surrounding, which explains whycation diffusion is relatively difficult. In comparison, cubic zirconia'smigrating oxygen only minimally disturbs neighboring Zr, which explains why itis a fast oxygen conductor.