X-RAY DIFFRACTION STUDY OF Nd_2-xCe_xCuO_4-y. I.P. Makarova¹, A. Bram², H.Burzlaff³. ¹Institute of Crystallography, Russian Academy of Sciences, 117333, Moscow, Russia; ²ESRF, BP220, 38043 Grenoble, France, ³Lehrstuhl fur Kristallographie, Institut fur Angewandte Physik der Universitat Erlangen-Nurnberg, 91054 Erlangen, Germany.

Changes in the atomic structure and the electron density distribution in single crystals of Nd_2-xCe_xCuO_4-y caused by Ce-doping have been studied using X-ray diffraction data. Four samples of Nd_2-xCe_xCuO_4-y have been investigated:

Nd₂CuO₄, 293 K, 20 K [1];

Nd₂-xCexCuO₄-y (I), x=16%, 293 K [2];

Nd₂-xCexCuO₄-y (II), x=13%, 293 K [2], 296 K, 150 K, 25 K;

Nd₂-xCexCuO₄-y (III), x=15%, HTSC, 293 K.

The main change on the electron density maps is the rearrangement of the charge density at the Cu position with Ce-doping, that indicates the change of the valence state of the Cu atom. At room temperature the formation of a density maximum at the Nd/Ce position was observed. As the temperature and the displacement parameters decrease, the maximum is split into six separated maxima, that may indicate the disordering at the Nd/Ce position. In contrast to the Ce-doped sample, no anomalious changes were observed in the undoped sample with temperature going down.

IPM thanks the ACA / US NCCr for granting.

1. I.P.Makarova, V.I. Simonov, M. Blomberg, M. Merisalo, accepted for publication in Acta Cryst.

2. I.P. Makarova, A.Bram, et al. (1994). Physica C, 223, 1.