The phase stability of La and Ni doped water-free and hydrated BaFeO3−δ perovskites and their electrical conductivity

Perovskite oxides with mixed ionic and electronic conductivity are promising electrode materials for solid oxide fuel cells. This study systematically investigates the influence of anionic composition and A - and B -site substitution on the crystal structure and conductivity of compounds synthesized by solid-state reaction (SSR) and nebulized spray pyrolysis (NSP). X-ray diffraction revealed strong dependencies of structural modifications on oxygen partial pressure and water incorporation. SSR-prepared compounds crystallized in hexagonal or monoclinic structures, while La substitution stabilized the cubic phase. In contrast, all NSP-synthesized samples exhibited an orthorhombic structure related to BaFeO 2.33 (OH) 0.33 . Iodometric titration showed maximum B-site oxidation states of +3.69 for air-synthesized La-free samples and +3.06 for La-doped NSP compounds. Conductivity increased with Ni content in SSR samples, whereas NSP materials showed strong dependence on Ni and water content. The highest conductivities reached 10 −2 and 10 −6 S cm −1 , respectively. Scanning electron microscopy additionally revealed spherical NSP particles and SSR agglomeration.