Structural stability, defects and competitive oxygen migration in Pr1-xYxBaCo2O6-δ

The ab initio projector augmented wave method of the density functional theory is applied for studying energy characteristics of oxygen vacancies and migration pathways inPr(1-x)Y(x)BaCo(2)O(6-delta). It is found that the negative formation energy leads to initial appearance of oxygen vacancies in PrO planes thus providing the pathway for oxygen migration at small delta's. The increase of oxygen vacancy population in PrO planes and replacement of Pr by Y both favor a weakening of Co-O bonds, which facilitates the increase in the amount of oxygen vacancies in CoO2 layers. Moreover, the yttrium dopants enlarge the bottleneck for oxygen jumps along <101> directions over oxygen vacancies in PrO and CoO2 layers. As a result, the respective 'zigzag' oxygen migration pathway becomes predominant with increasing oxygen non-stoichiometry and yttrium doping. Thus, the layered perovskite-like cobaltites give an example of a peculiar diffusion process where minority defects provide the transport channel while majority defects maintain favorable geometry of the migration pathway.