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.
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)
