XAFS and XRD study of ceria doped with Pr, Nd or Sm

Samples of ceria doped with Pr6O11, Nd2O3 or Sm2O3 at various doping fractions were prepared and occurring phases were examined by X-ray diffraction (XRD). Precise X-ray absorption fine structure (XAFS) measurements at rare-earth (RE) K and L-III edges were carried out for the solid solutions with the fluorite structure to investigate valences of the RE elements, and to determine interatomic distances between metal and oxygen and oxygen coordination numbers of RE elements. The oxygen vacancies were found to be neither distributed homogeneous over the crystal nor located just around the trivalent dopant. The doping was found to make the lattice expand but makes oxygen atoms move toward RE atoms, giving rise to the local distortion of the lattice. (C) 2004 Elsevier B.V. All rights reserved.