Metastable Ce-terminated (1 1 1) surface of ceria

Applications of ceria (CeO₂) in catalysis are closely related to the behavior of oxygen at the surface and subsurface. In this study, we show that the steps at the (1 1 1) surface of CeO₂ are highly reducible. Using aberration-corrected transmission electron microscopy, we observed simultaneous loss of surface and subsurface oxygen close to a step. Despite their large changes in atomic coordination, the outermost Ce atoms in the Ce-terminated surface has a negligible relaxation compared with the O-terminated surface. The outermost and subsurface Ce atoms of the Ce-terminated surface are reduced to valences of +1 and +3, and electronic configuration of 5s²5p⁶4f¹6s² and 5s²5p⁶4f¹, respectively. Both of them have a local magnetic moment and they couple antiferromagnetically. The existence of the Ce-termination is important for a complete understanding of the surface structure and properties of CeO₂.