Effects of oxygen non-stoichiometry on the physical properties of the YBaCo2O5+δYBaCo2O5+δ layered cobaltites

We have synthesized the layered cobaltites YBaCo2O5+δYBaCo2O5+δ with different oxygen contents (δ1δ1 and δ2δ2), and characterized its structural and physical properties using various experimental techniques within the 80–500 K temperature range. Two superstructures have been identified due to the ordering of oxygen vacancies. One of them (corresponding to δ≃0.50δ≃0.50) shows a metal–insulator transition at room temperature, while both exhibit a sequence of magnetic transitions AFM–FM–PM as the temperature is increased. We have determined the second-order nature of the FM–PM magnetic transition using the Banerjee criterion. We also show that there exist intrinsic differences between both samples in terms of the charge carriers involved, which manifest in the transport properties.