Here we report the results of thermogravimetric (TG) analysis on the oxygen
non-stoichiometry of RuSr2GdCu2O8 (Ru-1212) and
RuSr2(Gd0.75Ce0.25)2Cu2O10(Ru-1222) samples. With TG annealings carried out in
O2 and Ar atmospheres it was found that the oxygen content in Ru-1212 remains
less affected upon various annealings, while for Ru-1222 wider-range
oxygen-content tuning is possible. When heated in H2/Ar atmosphere the both
phases release oxygen upon breaking down to mixtures of metals (Ru and Cu) and
binary oxides (CeO2, Gd2O3, and SrO) in two distinct steps around 300 and 450
oC. This reductive decomposition reaction carried out in a thermobalance was
utilized in precise oxygen content determination for these phases. It was found
that the 100-atm O2-annealed Ru-1212 sample was nearly stoichiometric, while
the similarly treated Ru-1222 sample was clearly oxygen deficient. X-ray
absorption near-edge (XANES) spectroscopy was applied to estimate the valence
of Ru in the samples. In spite of the fact that the Ru-1212 phase was shown to
possess less oxygen-deficient RuO2 layer, the valence of Ru as probed with
XANES was found to be lower in Ru-1212 than that in Ru-1222.Comment: 11 pages text, 4 pages Figs. To ISS 2002 YOKOHAMA for PHYSICA
