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Jot of the ~ess~ommon beak, TEMPERATURE DEPENDENT SINGLE CRYSTAL X-RAY DIFFRACTION STUDY OF THE T* PHASE COMPOUND (La, 20Tbo ,?PbO 08)Cu04 P. BORDET’ , J.J. CAPPONI’ , C. CHAILLOUT’ , S-W. CHEONG3, J. CHENAVAS’ , Z. FfSK2, Th. FOURNIERI , J.L. HODEAUj , D.B. MC WHAN3, A. VARELA- LOSADA’ , M. MAREZIO’ 13 t Laboratoire de Cristallographie CNRS-UJF, 166X, 38042 Grenoble Cedex France, 2 Los Alamos National Laboratories, Los Alamos NM 87545, USA, 3 AT&T Belt Laboratories, Murray Hitf, NJ 07974, USA INTRODUCTION The 2:1:4 cuprate superconductors the K2NiF4-type, Ce)2CuO4-type’. respectively. are known to crystallize the Nd2CuO4-type For brevity discovered by 9 oxygen are surrounded structure the A’ cations are surrounded while the 6 cations are surrounded by apicaliy elongated octahedra. by 8 oxygen atoms arranged as a square prism, In the T’ structure the sequence of (AO) and (502) layers. layers is such that it comprises one half the T unit cell and one half the T unit cell. There are two sites for the large cations, one g-coordinated A inside the T/2 cell, and one &coordinated the T/2 cell. The 6 cations are surrounded pyramidal A’ inside by square pyramids forming corner-sharing layers. These layers are one of the common features for most of the cuprate high Tc superconductors. The compound (Nd, Sr, Ce)2Cu04-y superconducting phase was determined and high resolution by Akimitsu electron having the T’ structure et al. 2. The structural by the combined microscopy’. P4inmm with lattice parameters, structural differences It was found to be tetragonal, space group of a deoxidized, sample which had These authors carried out as well the non superconducting were found between the two structures. 0) layers which are apexes of the CuO5 pyramids ~22-508g~~3.50 to of the 7’ a = 3.86 A and c = 12.5 A. From neutron powder data, and found superconducting. refinement appreciable was reported arrangement use of X-ray and neutron powder diffraction, lzumi et al.3 refined the structure of a Ndl.32Sro.4tCeo.27CuO4.y been fully oxidized [(NdSr) In the T by four oxygen atoms arranged as a square. Since these squares are the remnants of octahedra, they form corner-sharing become neighbors in which the top four or bottom four anions have been replaced by one. The 6 cations alternately (Nd, Sr, they will be refered to as the T, T’ and T* phases, In the T structure the A cations are surrounded forming cuboctahedra with three structures, and the more recently sample. However, no The 02 atoms of the had a large thermal factor 0 Elsevier Sequoia, Printed in The Netherlands |
