We reviewed our various results on rutheno-cuprate magneto-superconductors RuSr2GdCu2O8(Ru-1212) and RuSr2(Gd0.75Ce0.25)2Cu2O10(Ru-1222). It is observed, that it is difficult to control the oxygen content of Ru-1212, though the same is possible up to some

sample that was not superconducting, even with various types of post-annealing treatments [27]. We will discuss this later.

As compared with Ru-1212, the Ru-1222 phase forms more easily in impurity-free form. Both the as-synthesized and the 100-atm O2-annealed Ru-1222 samples were found to be of high quality in terms of phase purity. An X-ray diffraction pattern for an as-synthesized sample is shown in Fig. 2. The lattice parameters were determined from the diffraction data in the tetragonal space group I4/mmm: a = b = 3.8337(6) Å and c = 27.493(1) Å for the as-synthesized sample, and a = b = 3.8327(7) Å and c = 27.393(1) for the 100-atm O2-annealed sample. The shorter lattice parameters for the 100-atm O2-annealed sample are believed to manifest the fact that it is more completely oxygenated than the as-synthesized sample.

RuSr2(Gd0.75Ce0.25)2Cu2O10-δ

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Relative Intensity

space group: I4/mmm

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2030

40502 θ (deg.)

60

Fig. 2. X-ray diffraction pattern for an as-synthesized RuSr2(Gd0.75Ce0.25)2Cu2O10-δ sample.

X-ray diffraction results, in terms of phase purity, space groups and the obtained lattice parameters are in general accordance with the reported literature [1,2,8,14,21-23].

3.2 Oxygen stoichiometry: TG results

Thermogravimetric reduction curves were recorded for both as-synthesized and 100-atm O2-annealed samples of Ru-1212 and Ru-1222 [28]. Two examples of the obtained TG curves are shown in Fig. 3. Upon heating in flowing H2/Ar gas both the phases, Ru-1212 and Ru-1222, release oxygen in a parallel manner decomposing to Ru metal, Cu metal and oxides of Sr, Gd and Ce in two distinct steps about 300 and 450 oC. Owing to the sharpness of the weight loss behaviour such reductive decomposition carried out in a thermobalance

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