Interface Solid-State Reactions in La_0.8Sr_0.2MnO₃/Ce_0.8Sm_0.2O₂ and La_0.8Sr_0.2MnO₃/BaCe_0.9Y_0.1O₃ Disclosed by X-ray Microspectroscopy

The stability of the electrode/electrolyte interface is a critical issue in solid-oxide cells working at high temperatures, affecting their durability. In this paper, we investigate the solid-state chemical mechanisms that occur at the interface between two electrolytes (Ce0.8Sm0.2O2, SDC, and BaCe0.9Y0.1O3, BCY) and a cathode material (La0.8Sr0.2MnO3, LSM) after prolonged thermal treatments. Following our previous work on the subject, we used X-ray microspectroscopy, a technique that probes the interface with submicrometric resolution combining microanalytical information with the chemical and structural information coming from space-resolved X-ray absorption spectroscopy. In LSM/BCY, the concentration profiles show striking reactive phenomena at the interface with a variety of micrometer-sized secondary phases: in particular, X-ray absorption spectra reveal at least three different chemical states for manganese (from +3 to +6). Also in LSM/SDC, a couple previously reported as chemically stable, we found the formation of small islets of SmMnO3 after the migration of manganese to the SDC side; these may constitute the nuclei for the subsequent formation of an interfacial resistive layer after more prolonged operation. The ability of manganese to adopt several oxidation states and crystal chemical environments is indicated as a possible cause for these behaviors.