Sr Segregation in Perovskite Oxides: Why It Happens and How It Exists

Among the phenomena related to the surface rearrangement of cations in perovskite-based oxides, A-site cation enrichment, Sr in particular, near the surface has been frequently observed. Upon annealing in an oxidizing atmosphere, Sr is often enriched on the surface as compared with the bulk composition of the material, which eventually forms Sr-rich phases or rearranges the crystal structure of the surface. This Sr segregation changes the structure and composition of the perovskite surfaces and thus affects the stability of the materials and the reactivity with gas phases. In this regard, many studies have been carried out in the field of solid oxide electrochemical cells (SOCs). In this review, we summarize the latest research efforts on Sr segregation in perovskite-based SOC O-2 electrodes, with a focus on how excess Sr is present. We then discuss the origins of Sr segregation and suggest strategies for suppressing it to realize high-performance perovskite-based O-2 electrodes.