The intrinsic defects, disordering, and structural stability of Ba xSr 1-xCo yFe 1-yO 3-δ perovskite solid solutions

First principles density functional theory modeling of point defects and structural disordering in Ba _xSr _1-xCo _yFe _1-yO _3-δ (BSCF) perovskites reveals that the material tends to decompose at low temperatures into a mixture of cubic and hexagonal perovskite and/or oxide phases. Special attention is paid to elucidating the effects of oxygen nonstoichiometry on cubic and hexagonal phase stability, decomposition energies, and oxygen vacancy formation energies. The observed lattice instability is likely to negate the advantages of the fast oxygen transport chemistry and impede the applicability of BSCF in solid oxide fuel cells and oxygen separation ceramic membranes. The general methodology presented here can be applied to analyze other candidate materials for many energy conversion applications.