Simultaneous quantification of ionic conductivity and defect concentrations in mixed ionic and electronic conducting oxide thin films

Mixed ionic and electronic conducting (MIEC) oxides are central to energy devices, but quantifying their intrinsic ionic transport and defect thermodynamics remains challenging in representative systems such as La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3−δ , where electronic conduction typically dominates and masks the much smaller ionic contribution. In this work, a method based on stoichiometry polarization and transmission line modeling of impedance data is proposed to extract the ionic conductivity and chemical capacitance of MIEC oxide thin films as functions of temperature and oxygen chemical potential. This framework enables the simultaneous determination of transport properties and defect concentrations from a single measurement. Moreover, it unlocks measurements at high oxygen chemical potentials (oxygen partial pressure » 1 bar) that are otherwise hardly accessible. Quantification of defect concentrations allows for the extraction of the partial molar enthalpy and entropy of lattice oxygen. The method provides a novel experimental route to investigate oxygen thermodynamics and transport in mixed conductors, and opens new possibilities for an in-depth understanding of functional oxide materials.