Assessment of CO(II), CO(III) and CO(IV) content in thermoelectric cobaltites

The precise content of cobalt at a given oxidation state in layered sodium or calcium cobaltites is crucial for their thermoelectric performance and stability at elevated temperature. The paper presents results of searching for an effective method of measuring cobalt ions concentration coexisting at various oxidation state in a solid state. Application of the specific properties of reagents gave possibility to determine Co³⁺ concentration in the presence of Co⁴⁺ by the wet chemical methods. The accuracy and usefulness of the method was checked by comparison of the results from independent measurement of the total cobalt content and sum of the cobalt concentration at various oxidation state. It has been found that separate concentration of cobalt at a various valence state can be precisely measured if no Co₃O₄ was present in the synthesized powders.