First-principles electronic-structure calculations on the stability and oxygen conductivity in Ba0.5Sr0.5Co0.8Fe0.2O3−δ

The perovskite-type compound Ba0.5Sr0.5Co0.8Fe0.2O3−δ has been investigated using quantum–theoretical methods. Density–functional calculations indicate a preference of the oxygen vacancy to be located close to cobalt instead of iron because of the higher affinity of oxygen towards iron. The energy barrier for an oxygen-hopping process was examined using the nudged elastic band (NEB) method. The resulting minimum-energy path is characterized by a correlation between the effective coordination number and the calculated energy: the lower the effective coordination number and the weaker the chemical bonding of the migrating oxygen atoms, the higher the energy. Also, the energy barriers appear to be slightly smaller when the oxygen atom passes an iron atom instead of a cobalt atom. Phonon calculations were carried out to achieve a thermodynamic analysis of B-site substituted BSCF5582 as a function of temperature. Theory suggests that substitution of cobalt by nickel destabilizes the structure whereas Mn-doped BSCF is favored over the unsubstituted compound in a wide temperature range between 0 and 1600 K.