Protons in (Ga,Sc,In,Y)3+-doped BaFeO3 triple conductors — Site energies and migration barriers investigated by density functional theory calculations

BaFeO 3-δ is a prototypical “triple-conducting” perovskite combining electronic, proton and oxygen vacancy conductivities. Here, the interaction energies of protons at different sites with Ga 3+ , Sc 3+ , In 3+ , and Y 3+ dopants on the Fe site in BaFeO 3 are calculated using density functional theory (DFT). The effect of the dopants on the respective proton transfer barriers is also investigated. While for the smaller Ga 3+ and Sc 3+ dopants a slight trapping of protons in the first and second shell around the dopant is found, in the case of the strongly oversized In 3+ and Y 3+ the first shell exhibits a repulsive behaviour for protons (despite attractive electrostatic interaction). The calculated proton transfer barriers for different configurations depend sensitively on the local geometry. They follow the previously derived correlations with O-H bond lengths and O···O distances in BaFeO 3-δ , corroborating that these quantities are physically meaningful descriptors for proton transfer in perovskites. Overall, a very complex energy landscape is obtained, and the consequences for long-range proton transport are discussed only qualitatively. The combination of a proton-repulsive first shell and the tendency for increased proton barriers suggests that for BaFeO 3-δ , instead of the very oversized Y 3+ smaller dopants should be considered. • Extended DFT study of proton site energies and barriers in doped BaFeO 3 . • Repulsive zone around very oversized Y 3+ . • Increased proton transfer barriers around very oversized Y 3+ . • Qualitative discussion of long-range transport.