Electrochemical polarization dependence of the elastic and electrostatic driving forces to aliovalent dopant segregation on LaMnO3

Maintaining a stable surface structure and composition is important for retaining long-term reactivity to oxygen exchange reactions on perovskite oxides in energy conversion applications. A common detrimental surface evolution is the segregation of aliovalent dopant cations, for example Sr2+ in La1-xSrxMnO3 (LSM). This process is known to be activated at elevated temperatures. Here we focus on resolving the effect of the oxygen chemical potential, which varies over a wide range in electrochemical and thermochemical energy conversion reactions. We employ electrochemical polarization to tune the oxygen chemical potential over many orders of magnitude, quantify the resulting segregation by X-ray photoelectron spectroscopy, and employ ab-initio thermodynamics calculations to rationalize our findings. Ca-, Sr-, and Ba-doped LaMnO3 is selected as a model system, where the dopants have the same charge but different ionic sizes. Altering the effective oxygen chemical potential alters the oxygen non-stoichiometry ...