Interaction of monoclinic ZrO2 grain boundaries with oxygen vacancies, Sn, and Nb: Implications for the corrosion of Zr alloy fuel cladding

We used density-functional-theory simulations to examine the structural and electronic properties of the Σ3180∘(100)[001] grain boundary in monoclinic ZrO2, which is a very low-energy (0.06Jm−2) twin boundary present in experimental oxide texture maps, with suggested special properties. This equilibrium structure was compared with a metastable structure (with a boundary energy of 0.32Jm−2). The interaction of oxygen vacancies, substitutional Sn and Nb defects (substituting host Zr sites) with both structures—and their effect on the boundary properties—were examined. We found that the equilibrium structure energetically favors VO2+ and NbZr2−, whereas the metastable structure favors VO2+ and SnZr2−. Tin was further found to bind strongly with oxygen vacancies in both structures and introduce gap states in the band gap of their electronic structure. SnZr2− was, however, found to increase the segregation preference of VO2+ for the metastable structure, which might contribute to increased oxygen and electron transport down this interface, and therefore other less special boundaries, compared to the equilibrium structure of the studied monoclinic twin boundary. Published by the American Physical Society 2025