Local Structure of the Metal-oxygen Bonds in ZrO2-CeO2 Nanopowders

I.O. FÁBREGAS; R.O. FUENTES; D.G. LAMAS; M.E. RAPP; N.E. WALSÖE DE RECA; A.F. CRAIEVICH; M.C.A. FANTINI

Florencia, italia

Congreso; XX Congress of the International Union of Crystallography and General Assembly; 2005

International Union of Crystallography

Resumen publicado en Acta Cryst. (2005). A61, C155 Zirconia-ceria solid solutions are being widely employed in current automotive three-way catalysts as oxygen storage promoters due to their excellent catalytic properties. These properties have been proposed to be related to the local structure of the metal-oxygen bondsin these materials.In this work, the local structure around Zr and Ce atoms in compositionally homogeneous, nanocrystalline ZrO2-CeO2 powders was investigated by the technique named extended X-ray absorption fine structure (EXAFS). These experiments were carried out at the D04B XAS-1 beamline of LNLS (Brazilian Light Facility). ZrO2-15, 40, 50, 60, 65, 70, 80 and 90 mol% CeO2 nanopowders were synthesized by a pH-controlled nitrate-glycine gel-combustionprocess. While Ce-O coordination sphere has a cubic symmetry in the whole composition range, the Zr-O coordination shows a tetragonal-to-cubic symmetry change as the CeO2 content is varied. This transition was found to be at (85 +/- 5) mol% of CeO2, in agreement with a previous synchrotron XRD study. For compositions with a tetragonal crystal structure, a 5+2 model was found for the Zr-O bond, while the coordination number was 5 for the cubic solid solutions. The coordination number of Ce was close to 8 for all the compositions. Finally, we also demonstrated that the local structure determined by EXAFS agrees well with the long-range structure deduced by XRD.