In the crystallization process, the two phases acquire a different Sr content. As proven by analysis of the lattice constants and TEM-EDX, the perovskite phase becomes depleted in Sr which strongly decreases its oxygen exchange activity, while the activity of the Ruddlesden-Popper phase is hardly affected by the increased Sr concentration. This has to be considered when conparing the oxygen reduction activity (measured by impedance spectroscopy on microelectrodes) of single-phase with two-phase films.
S. Stämmler, R. Merkle, B. Stuhlhofer, G. Logvenov, and J. Maier
Influence of Hetero Grain Boundaries on Oxygen Exchange Activity: Investigation of Two-phase (La,Sr)CoO3-δ /(La,Sr)2CoO4+δ Cathode Materials
ECS Transactions, accepted, 2015.