Subtleties in the structure and magnetic properties of the triple conducting perovskite, BaCo0.4Fe0.4Zr0.1Y0.1O3–δ

Due, in part, to its simultaneous transport of protons, electrons, and oxygen ions, BaCo0.4Fe0.4Zr0.1Y0.1O3–δ (BCFZY4411) is an archetypal triple-conducting oxide (TCO) and a promising candidate for the air electrode of protonic ceramic electrochemical cells. While the average nuclear structure of BCFZY4411, a cubic perovskite, is well established, several important details such as possible short-range ordering on the B site and the location of protons, features which would be expected to impact transport, are unknown. Here we apply neutron diffraction and magnetometry to probe the nuclear and magnetic structure of BCFZY4411 in both the dried state and after exposure to steam/air atmosphere. We observe a transition from short-range antiferromagnetic correlations at room temperature to uncompensated antiferromagnetic behavior with slight ferromagnetic ordering at low temperatures. The short-range magnetic correlations persist through 500 K, revealing the effects of a complex spin structure and oxidation landscape in this cubic perovskite. Rietveld refinements of neutron diffraction data show a 2–3% decrease in oxygen site vacancies, reduction in O and B site atomic displacement parameters, lattice contraction, and reduced magnetic phase-transition temperature upon exposure to steam. The hydrogen content in the steam-treated material is estimated to be below 0.15 at%, indicating that the observed changes in structure and magnetic properties are largely due to oxidation. The result indicates that a high proton concentration is not a prerequisite for high electrochemical activity. The comprehensive crystallographic analysis presented here furthermore paves the way for future quantitative studies of local atomic structure in this and other TCO systems.