Oxygen ordering in the high-Tcsuperconductor HgBa2CaCu2OAuthor(s) - Teresa Mendonça, J. G. Correia, H. Haas, P. Odier, Pedro B. Tavares, M. R. da Silva, A. M. L. Lopes, André M. Pereira, J. N. Gonçalves, João S. Amaral, Céline Darie, João P. Araújo

International audienceLattice sites and collective ordering of oxygen atoms in HgBa2CaCu2O6+delta were studied using the perturbed angular correlation (PAC) technique at ISOLDE/CERN. The electric field gradients (EFG) at Hg-199m nuclei have been measured as functions of oxygen doping on the Hg planes, above and below T-c. In comparison with the results obtained for oxygen and fluorine doping in Hg-1201, the analysis shows a different oxygen ordering exhibited by Hg-1212. Moreover, for all studied cases, the experimental results show that at a local scale there is non uniform oxygen distribution. A series of ab initio EFG calculations allowed to infer that at low concentrations, regions without oxygen coexist with regions where O-2 delta dumbbell molecules are located at the center of the Hg mesh. On the other side, at high concentrations, O-2 delta dumbbell molecules coexist with single O-delta atoms occupying the center of the Hg mesh. The present results suggest that oxygen sits on the Hg planes in the form of a molecule and not as a single atom