Cation diffusion and segregation at the interface between samarium-doped ceria and LSCF or LSFCu cathodes investigated with X-ray microspectroscopy

The chemical compatibility between electrolytes and electrodes is an extremely important aspect governing the overall impedance of solid-oxide cells. Since these devices work at elevated temperatures, they are especially prone to cation interdiffusion between the cell components, possibly resulting in secondary insulating phases. In this work, we applied X-ray microspectroscopy to study the interface between a samarium-doped ceria electrolyte and lanthanum ferrite cathodes (La0.9Sr0.1Fe0.85Cu0.15O3 - LSCF; La0.4Sr0.6Fe0.8Co0.2O3 - LSFCu), at a submicrometric level. This technique allows to combine the information about the diffusion profiles of cations on the scale of several micrometers, together with the chemical information coming from space-resolved X-ray absorption spectroscopy. In SDC-LSCF bilayers, we find that the prolonged thermal treatments at 1150 °C bring about the segregation of samarium and iron in micrometer-sized perovskite domains. In both SDC-LSCF and SDC-LSFCu bilayers, cerium diffuses into the cathode perovskite lattice A-site as a reduced Ce3+ cation, while La3+ is easily incorporated in the ceria lattice, reaching 30 at.% in the ceria layer in contact with LSFCu.