Eur. Phys. J. B 41, 31-42 (2004)
https://doi.org/10.1140/epjb/e2004-00290-x

Local structure around Ce in the Nd_2-xCe_xCuO_4±δ superconductor probed by EXAFS

¹ INSTM, C.S.T.E./CNR, and Dipartimento di Chimica Fisica, Università di Pavia, Viale Taramelli 16, I 27100, Pavia, Italy
² CNR Istituto Struttura della Materia, Via Fosso del Cavaliere 100, 00133 Roma, Italy
³ Istituto Nazionale di Fisica Nucleare & Dipartimento di Fisica, Università di Roma III, Via della Vasca Navale 84, 00146 Roma, Italy
⁴ Dipartimento di Chimica Fisica ed Elettrochimica, Università di Milano, via C. Golgi, 19, 20133 Milano, Italy
⁵ Istituto CNR di Scienze e Tecnologie Molecolari ISTM, via C. Golgi, 19, 20133 Milano, Italy

Corresponding author: ^a paolo.ghigna@unipv.it

Received: 30 October 2002
Revised: 19 February 2004
Published online: 30 September 2004

Abstract

The local structure around the Ce substitutional defects has been investigated by Ce and Nd K-edge EXAFS on Nd_2-xCe_xCuO samples with different dopant concentrations (x = 0.05, 0.10, 0.15 and 0.20) and oxygen amounts. The lattice distortion around the Ce can be described as a shrinkage of the oxygen cuboid along the z crystallographic direction. Moreover, the CuO₄ planes become corrugated. The lattice distortion is well localized and is largely independent of temperature and Ce and oxygen content. EXAFS measurements made at the Nd-K edge indicate that the local chemical environment of Nd is not distorted. The difference electron density maps, obtained from low temperature single crystal X-ray diffraction data, revealed three strong positive residuals which have been ascribed to cerium (at 0, 0, ) and to two non equivalent oxygen apical positions O3 (at 0, 0, ) and O4 (at 0, 0 ). The electron population of O4 site, which is closer to cerium ( Å), is 3-4 times the O3 one.