Evidence for Oxygen Vacancies in Misfit-Layered Calcium Cobalt Oxide, [CoCa2O3]qCoO2

We have synthesized samples of the misfit-layered [CoCa2O3]qCoO2 compound with three different oxygen contents and characterized them by both wet-chemical and thermogravimetric analyses for the determination of precise oxygen content, and by synchrotron X-ray diffraction for the precise determination of the magnitude of q. Combining the results from the structural and oxygen-content analyses it is concluded that for samples synthesized in air or a more reducing atmosphere there occur considerable amounts of oxygen vacancies in at least one of the three types of layers, CoO, CaO, and CoO2. Bulk character of the oxygen vacancies was confirmed from transport-property measurements