2, University of Seoul, Seoul, , Korea (the Republic of)
Surface cation segregation and phase separation, of strontium in particular, has been suggested to be the key reason behind the chemical instability of perovskite oxide surfaces and the corresponding performance degradation of solid oxide electrochemical cell electrodes. However, there is no well-established solution for effectively suppressing Sr-related surface instabilities. Here, we control the degree of Sr-excess at the surface of SrTi0.5Fe0.5O3-δ thin films, a model mixed conducting perovskite O2-electrode, through lattice strain, which significantly improves the electrode surface reactivity. Combined theoretical and experimental analyses show that Sr cations are intrinsically under a compressive state in the SrTi0.5Fe0.5O3-δ lattice and that the Sr-O bonds are weakened by the local pressure around the Sr cation, which is the key origin of surface Sr enrichment. Based on these findings, we successfully demonstrate that when a large-sized isovalent dopant is added, Sr-excess can be remarkably alleviated, improving the chemical stability of the resulting perovskite O2-electrodes. Furthermore, in-situ characterizations of lattice strain and surface composition of STF thin films will be discussed for clarifying the behavior of strontium cations at various temperatures.