Oxygen stoichiometry in Co-1212, Co-1222 and Co-1232 of the homologous series Co-12s2 of "category-B" layered copper oxides

The results of a systematic study on oxygen stoichiometry are reported for the first three members of the novel CoSr2(Y,Ce)(s)Cu2O5+2s+/-delta or Co-12s2 homologous series, i.e. Co-1212, Co-1222 and Co-1232 phases, with a SrO-CoO1+/-delta-SrO-CuO2-(Y,Ce)-[O-2-(Y,Ce)](s-1)-CuO2 layered structure. The oxygen content was precisely determined by two independent chemical techniques: coulometric Cu+/Cu2+ titration and iodometric titration. Furthermore, oxygen stability/tunability was investigated by means of oxygenative and reductive annealings carried out in a thermobalance. It was revealed that all the three phases are rather stoichiometric in oxygen content (delta approximate to 0) and stable against both oxygenative and reductive annealings. The present results provide us with an indication that the nominally oxygen-stoichiometric B-[O-2-B](s-1) "fluorite block", the characteristic structural element for all layered copper oxides of "category-B" [H. Yamauchi, M. Karppinen, Superlatt. Microstructr. 21A (1997) 128], is non-tunable in terms of the oxygen content not only in the Co-12s2 (s > 1) phases but also in other category-B phases. (C) 2003 Elsevier B.V. All rights reserved.