AVS 47th International Symposium
    Surface Science Wednesday Sessions
       Session SS1+MC-WeA

Paper SS1+MC-WeA9
Self-Diffusion in Ceria

Wednesday, October 4, 2000, 4:40 pm, Room 208

Session: Oxide Surfaces, Interfaces and Defects
Presenter: C.L. Perkins, Pacific Northwest National Laboratory
Authors: C.L. Perkins, Pacific Northwest National Laboratory
M.A. Henderson, Pacific Northwest National Laboratory
G.S. Herman, Pacific Northwest National Laboratory
Correspondent: Click to Email
Ceria, an oxygen storage material vital to the proper functioning of automobile three-way catalysts, is typically viewed as an anion conductor. In light of mounting evidence that in the prototypical oxide rutile TiO@sub 2@ the mobile species are Ti cations rather than O anions, the diffusivities of both cerium and oxygen in ceria were explored via temperature programmed static secondary ion mass spectrometry (TPSSIMS). The 500 Å thick CeO@sub 2@(111) film was heteroepitaxially grown by molecular beam epitaxy on a yttria stabilized zirconia substrate. Although high quality LEED patterns and Auger spectra free of signals from elements other than cerium and oxygen were obtained after just a few sputtering and annealing cycles, further cleaning was necessary to remove intense alkali and alkaline earth signals observed in SSIMS. The CeO@sub 2@(111)surface was slightly enriched in @super 18@O by first annealing the film in UHV at 830 K and then exposing the 130 K crystal to @super18@O@sub 2@. TPSSIMS data in conjunction with temperature programmed desorption (TPD) data demonstrate that surface oxygen begins to diffuse into the bulk around 550 K. Physical deposition in an @super18@O@sub 2@ background of submonolayer amounts of isotopically enriched cerium (@super 136@Ce) allowed the simultaneous study of the diffusivity of both cerium and oxygen. Surface cerium cations were found to be immobile with respect to diffusion into the bulk up to the highest temperature studied, 900 K.