Surface composition of ceramic CeGd-oxide

The atomic composition of the outermost atomic layers of gadolinium-doped ceria, Ce0.8Gd0.2O1.9, was determined with Low Energy Ion Scattering (LEIS), Due to the surface sensitivity of this technique it was possible to determine that the outer 5 monolayers are Gd-enriched, The Ce/Gd ratio changes from 1 at the outermost surface to 4.2 in the 'bulk'. When this ceria would be used as the electrolyte in a fuel cell, such a surface Gd enrichment could influence its operation. Only in the first monolayer was some Ca observed. No difference in surface composition was observed between samples sintered at 1300 and 1600 degrees C, in spite of large differences in oxygen ionic-conductivity observed previously. At a depth of about 20 monolayers a sudden shift in surface conductivity is observed that might be correlated with a structural change of the material at the grain boundary. The quantification with LEIS was checked with Rutherford Backscattering Spectroscopy (RBS), giving good agreement for the bulk composition. (C) 1998 Elsevier Science B.V. All rights reserved.