ELECTRONIC-STRUCTURE OF ND1.85CE0.15CUO4-DELTA, IRRADIATED BY HE- AN X-RAY-ABSORPTION STUDY ON THE CU-L-3 AND CE-M-4,M-5 EDGES( IONS )

Polarisation-dependent x-ray absorption spectroscopy at the Cu L-3 and Ce M-4,M-5 edges have been performed on the epitaxial films Nd1.85Ce0 .15CuO4-delta vs. defect concentration induced by He+ ion irradiation. The Cu L-3 edge exhibits increasing of integral intensity of both the white line in E parallel to ab and the first peak in E parallel to c by about 15% and 30%, respectively, after suppression of superconducti vity. The partial filling of Ce 4f orbitals (similar to 15%) takes pla ce although the Ce ions remain formally tetravalent, Ce+4. Thus, XAS e xperiments give a clear evidence that the excess electrons leave Cu 3d (x)(10)2(-y)2 orbital and become simultaneously localised in the Ce-O( 2) chains. The symmetry of the free states and the mechanism of superc onductivity suppression in Nd1.85Ce0.15CuO4-delta under He+ ion irradi ation are discussed.