Oxygen Stoichiometry in Co-1212, Co-1222 and Co-1232 of Homologous Series Co-12s2 of Category-B Layered Copper Oxides

TL;DR

This study systematically investigates oxygen stoichiometry in the first three members of the Co-12s2 homologous series, revealing their stable, nearly stoichiometric oxygen content and non-tunability in oxygen levels.

Contribution

It provides the first detailed analysis of oxygen content and stability in Co-1212, Co-1222, and Co-1232 phases, demonstrating their structural stability and non-tunability of oxygen content.

Findings

All three phases are nearly stoichiometric in oxygen content.

The phases are stable against oxygenative and reductive annealing.

Oxygen content is non-tunable in these structures.

Abstract

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.