  Here results of a systematic study on oxygen stoichiometry are reported for
the first three members of the novel CoSr2(Y,Ce)sCu2O5+2s or Co-12s2 homologous
series, i.e. Co-1212, Co-1222 and Co-1232 phases with a
SrO-CoO1-SrO-CuO2-(Y,Ce)-[O2-(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
an-nealings carried out in a thermobalance. It was revealed that all the three
phases are rather stoichiometric in oxygen content and stable against both
oxygenative and reductive an-nealings. The present results for the Co-12s2
homologous series suggest that not only the CoO1 charge reservoir but also the
nominally oxygen-stoichiometric B-[O2-B]s-1 fluo-rite block, that is the
characteristic structural element for the Co-12s2 (s > 1) phases and all other
layered copper oxides of category-B [H. Yamauchi and M. Karppinen, Superlatt.
Microstructr. 21A (1997) 128] is non-tunable in terms of the oxygen content.
