Oxygen non-stoichiometry in Ru-1212 and Ru-1222 magnetosuperconductors

We report here the results of thermogravimetric (TG) analysis on the oxygen non-stoichiometry of RuSr2GdCu2O<f>8−δ</f> (Ru-1212) and RuSr2(Gd0.75Ce0.25)2Cu2O<f>10−δ</f> (Ru-1222) samples. With TG measurements carried out in O2 and Ar atmospheres it is found that the oxygen content in Ru-1212 remains less affected upon various annealings, while for Ru-1222 the 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 simple oxides (CeO2, Gd2O3, and SrO) in two distinct steps around 300 and 450 °C. This reductive decomposition reaction carried out in a thermobalance is utilized in precise oxygen content determination for these phases. It is found that the 100-atm O2-annealed Ru-1212 sample is nearly stoichiometric, while the similarly treated Ru-1222 sample is clearly oxygen deficient. X-ray absorption near-edge structure (XANES) spectroscopy is 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 RuO<f>2−δ</f> layer, the valence of Ru as probed with XANES is found to be lower in Ru-1212 than in Ru-1222. [Copyright &y& Elsevier]