17O NMR in planes and chains of YBa2Cu3O7

2014 We report the first observation of 17O NMR spectra in YBa2Cu3O7 obtained after selective gas exchanges performed at 300 and 850°C. We are able to assign the narrow (weakly shifted) signal to the (1/2, 1/2) transition of oxygen atoms in CuO chains and the broad (strongly shifted) signal to the 0-sites in CuO2 planes. J. Phys. France 49 (1988) 1825-1828 NOVEMBRE 1988, Classification Physics, Abstracts 76.60C 74.30G 74.70V Up to now high temperature superconductivity has only been observed in oxygen containing materials (ternary or quaternary copper oxides). The structure of these materials reveals the existence of either CuO2 planes or a combination of CuO2 planes and CuO chains as in the’ orthorhombic phase of YBa,2CU307-,6 Oxygen atoms play a crucial role in these materials. i) The concentration of oxygen atoms determines the actual valence state of Cu. ii) It has been argued that charge carriers in YBa2 Cu3 07 are holes in the predominantly oxygen 2p band of the Cu02 planes. Furthermore, oxygen is known to be fairly mobile in the structure even temperatures as low as 300° C. Neutron diffraction studies [1] of the orthorhombic structure 6.57-67 have shown that oxygen atoms can occupy five different crystallographic sites. Sites 0(1) and 0(5) are lying within the ab-plane but only 0(1) sites are filled as long as 6 is small forming Cu-0 chains along the b-direction. 0(2) and 0(3) sites lie in CuO2 layers adjacent to Y atoms whereas 0(4) sites are located in planes parallel to the c-direction. We report an NMR study of 110 nuclei allowing a clear-cut assignment of NMR signals to planes and chains sites. The starting material was prepared by a chemical route [2] using liquid nitrate precursors in order to achieve an excellent chemical homogeneity checked by electron microprobe. After a post-treatment (2 hours at 850° C in 02) this process leads to powders exhibiting a monomodal distribution of particles Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphys:0198800490110182500