Oxygen ordering in the high-Tcsuperconductor HgBa2CaCu2O

Tânia Mendonça

¹

,

J. G. Correia

²

,

H. Haas

³

et al.

Abstract

Lattice sites and collective ordering of oxygen atoms in HgBa2CaCu2O 6+δ were studied using the Perturbed Angular Correlation (PAC) technique at ISOLDE/CERN. The electric field gradients (EFG) at 199m Hg nuclei have been measured as function of oxygen doping on the Hg planes, above and below TC. 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 2δ dumbbell molecules are located at the centre of the Hg mesh. On the other side, at high concentrations, O 2δ dumbbell molecules coexist with single O δ atoms occupying the centre of the Hg mesh.

Monitoring LaMnO 3 Jahn–Teller distortion via electric-field gradient ab initio calculations

“…Several experimental techniques are able to measure the EFG. On the other hand, the EFG can be calculated from the charge density obtained in an ab initio electronic structure calculation and has been proven to be a very sensi tive quantity [30][31][32][33][34].…”