SURFACE-COMPOSITION OF CERAMIC CEGD-OXIDE

The atomic composition of the outermost atomic layers of gadolinium-do ped ceria, Ce0.8Gd0.2O1.9, was determined with Low Energy Ion Scatteri ng (LEIS), Due to the surface sensitivity of this technique it was pos sible 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, suc h a surface Gd enrichment could influence its operation. Only in the f irst monolayer was some Ca observed. No difference in surface composit ion was observed between samples sintered at 1300 and 1600 degrees C, in spite of large differences in oxygen ionic-conductivity observed pr eviously. At a depth of about 20 monolayers a sudden shift in surface conductivity is observed that might be correlated with a structural ch ange of the material at the grain boundary. The quantification with LE IS was checked with Rutherford Backscattering Spectroscopy (RBS), givi ng good agreement for the bulk composition. (C) 1998 Elsevier Science B.V. All rights reserved.