THE ATOMIC AND ELECTRONIC-STRUCTURE OF CERIUM SUBSTITUTIONAL DEFECTS IN ND2-XCEXCUO4+DELTA AN XAS STUDY

The local atomic and electronic structure of cerium substitutional defects in Nd1.80Ce0.20CuO4+delta Was investigated by means of X-ray absorption spectroscopy (EXAFS and XANES of Ce L(III) edge), as a function of the oxygen partial pressure. It has been found that in all of the experimental conditions investigated (1, 10(-3) and 10(-6) atm), the Ce formal oxidation state should be regarded as IV, This is explained in terms of the bond configuration in this material. The consequences for the electron counting in the CuO2 planes are discussed. As is shown by EXAFS, the increased charge on the 4e site in the T' structure mandates a local lattice distortion around cerium: the co-ordination cuboid collapses along the (001) direction. Consequently, the Ce-O bond length is shorter than the Nd-O bond length.