Feb 6 – 8, 2006
CERN
Europe/Zurich timezone

Studying atomic order of oxygen dopants in high TC superconductors

Feb 7, 2006, 5:35 PM
15m
Council Chamber, 503/1-001 (CERN)

Council Chamber, 503/1-001

CERN

CH-1211 Geneva 23

Speaker

T. M. Mendonça (Dep. Física, Instituto Tecnológico e Nuclear E.N. 10, P - 2686-953 Sacavém)

Description

We present a progress report of lattice sites and collective ordering studies of dopant oxygen atoms in HgBa2CaCu2O6.26 (Hg1212) samples with the perturbed angular correlation technique, PAC. By measuring electric field gradients (EFG) at 199mHg nuclei, information for characterizing the oxygen atoms, Oδ, which go to the Hg- planes and dope the superconducting CuO2 planes with double-hole charge carriers is obtained. Due to the synthesis complexity of such materials an overview of the production methods is presented. A new process of producing highly pure precursors, CO2 free, has been developed, previously to the final step where Hg is introduced under very high pressure annealing. This was an essential work to obtain the pure phase of Hg1212 samples. At ISOLDE small powder samples of Hg1212 were then implanted with low doses of 199mHg and first annealed to remove implantation defects. The PAC experiments have been performed under different Ar or O2 annealing conditions, up to 25 bar O2 pressure. While we identify different concentrations of oxygen atoms, depending on the annealing process, the maximum achieved concentration with δO < 0.26 was still low. In this situation most of the oxygen atoms occupy, as expected, mainly single interstices at the centre of the Hg mesh without collectively ordering. However, experiments performed after different annealing conditions and measured at different temperatures, have revealed differences in the charge distribution of the Hg surroundings, still under analysis. PAC experiments on Hg1212 and HgBa2Ca2Cu3O8 are being prepared where the samples should be annealed under higher O2 pressures, up to 100 bar, to obtain higher dopant concentrations.

Primary author

T. M. Mendonça (Dep. Física, Instituto Tecnológico e Nuclear E.N. 10, P - 2686-953 Sacavém)

Co-authors

A. M. Gomes (CBPF/ UFRJ, Rio de Janeiro 22290-180 Brazil) J.G. Correia (Dep. Física, Instituto Tecnológico e Nuclear E.N. 10, P - 2686-953 Sacavém) J.P. Araujo (Dep. Física and IFIMUP, Univ. Porto, Rua do Campo Alegre, P-4169-007 Porto) P. Odier (Lab. Crystalographie, CNRS, Av. des Martyrs 25, F-38042 Grenoble CEDEX 9) P.B. Tavares (Dep. Química, Centro de Química, Univ. Trás-os-Montes e Alto Douro, Vila Real P-5001-911)

Presentation materials