Metastable Ce-terminated (111) Surface of Ceria

Abstract 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.