Study of oxygen ordering in HT_csuperconductors by magnetic resonance of different nuclei

NMR Studies of the Normal State of High Temperature Superconductors

“…Working on such oriented powders with Ho II c-axis is equivalent to work on single crystals-When Ho is perpendicular to the c-axis, two diflerent situations are encountered: if there is no detectable asymmetry of the tensor in the ab-plane (which is the case for the planar copper) the spectrum is again similar to that obtained in a single crystal. However, when the largest component of the tensor lies in the ab-plane (copper in the chains of YBa2Cu306+x, Planar oxygen) one obtains a broad 2D Hamiltonian-Studies of the EFG tensor provide valuable information about the site symmetry and the degree of disorder in the local environment [26,27] A recent development is worth being noted: thanks to the increasing number of NMR studies in various systems, it seems that all compounds having a high (or potentially high) T~show systematically relatively low vQ values for Cu in the Cu02 Planes. This behavior, first noted by Zheng et ai.…”