INFLUENCE OF THE CERIUM-OXYGEN CHARGE-TRANSFER ENERGY ON THE CERIUM EXCITATION-SPECTRA OF OXIDES - A CE L(3) XAS STUDY OF CERIUM-DOPED YTTRIUM-OXIDE

We have studied the influence of the mean Ce-O distance on the Ce L(3) X-ray absorption spectra (XAS), for a given eight-fold oxygen coordin ation, like in CeO2 (cubic symmetry). For that purpose, solid solution s of cerium-doped Y2O3 (2 at% and 5 at%) were synthesised. The local a tomic arrangement in the solid solutions, as deduced from the EXAFS (E xtended X-ray Absorption Fine Structures) measurements, is well repres ented by a 8-fold oxygen coordination around the cerium atoms like in CeO2, with a Ce-O distance of 2.28 Angstrom as in Y2O3, shorter than i n CeO2 (2.34 Angstrom). This shortening of the Ce-O distance increases the Madelung field acting on the electrons of the cerium atoms, and l eads to an increase of the charge transfer energy between cerium and o xygen. This affects the shape of the Ce L(3) X-ray absorption spectrum of the solid solutions, compared to that of CeO2. The changes observe d can be explained in the framework of the multielectronic configurati on-mixing model.