O vacancy formation in (Pr/Gd)BaCo₂O_5.5 and the role of antisite defects

In search for materials for intermediate temperature solid oxide fuel cells, (Pr/Gd)BaCo₂O_5.5 is investigated by first principles calculations. Antisite defects are considered as they may modify the electronic and O diffusion properties but are rarely studied in double perovskite oxides. Octahedrally coordinated Co atoms are shown to realize intermediate and high spin states for PrBaCo₂O_5.5 and GdBaCo₂O_5.5, respectively, while pyramidally coordinated Co atoms always have high spin. It turns out that O vacancy formation is significantly easier in PrBaCo₂O_5.5 than in GdBaCo₂O_5.5, the difference in formation energy being hardly modified by antisite defects. While pyramidally coordinated Co atoms are not affected, we show that the presence of antisite defects causes parts of the octahedrally coordinated Co atoms to switch from intermediate to high spin.